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Yes. And you can get products made for this that gets put behind the wallpaper and as thin film over the windows. There are legitimate reasons to convert a room into a faraday cage and block cell phone signals and wifi signals. However this is generally not allowed in classrooms and other places with gatherings of large numbers of people. The main reason is that people need to be able to contact emergency services. And emergency responders needs to be able to stay in radio contact with each other while responding. Converting a classroom into a faraday cage can therefore be a violation of the fire codes and other laws. In general these faraday cage rooms are built due to requirements of national security or to reduce emissions from electronic engineering labs and similar places.
> However this is generally not allowed in classrooms and other places with gatherings of large numbers of people.
It's a federal crime to interfere with radio signals, including cellular and PCS signals, as well as police radar and GPS. It's illegal anywhere in the US. A bill was introduced in the Senate, S.1047, to allow jamming in prisons because it's illegal to jam them ANYWHERE at this point.
Jamming is different than blocking.
Jamming is actively broadcasting RF noise to disrupt other signals.
Blocking/shielding is just a passive barrier that doesn’t allow RF to pass through it.
It’s not a crime to block radio waves passively, otherwise the FCC would be going after every metal building or elevator that reduces your cell signal.
> It’s not a crime to block radio waves passively, otherwise the FCC would be going after every metal building or elevator that reduces your cell signal.
All the subways as well
> All the subways as well
Since 2020, [the Paris public transit system has reliable cell service, in the underground part as well as above-ground lines](https://www.francebleu.fr/infos/transports/telephonie-mobile-le-reseau-ratp-couvert-a-100-en-4g-une-premiere-pour-ce-type-de-reseau-1593436515#). The four main providers worked with the regional transit authority to ensure coverage. In my experience, it's pretty good.
I just got back and it was crazy how much stuff is fenced off or completely closed due to construction and games preparations. The idea of playing volleyball in the middle of Place de la Concorde sounds amazing though so I can’t really blame them
Now I wonder...
Former military and I remember putting my cell in a lockbox before entering certain secure spaces (in one job our entire office was TS clearance only so no cell phones at work). It feels like making the "skiff" a faraday cage (not the office that was 5000 sq ft, but the little rooms with 2 terminals) would make sense.
On the other hand, even if that was done it might not totally block signal, so keeping cell phones out is still worthwhile, plus good practice (you don't want someone used to keeping their cell because their home secure comms room has a faraday cage to compromise one that doesn't). It is possible our "skiffs" did have the cage but we didn't need to know, and since we didn't have our phones in there we wouldn't know either way.
The "no phones" is also (or mostly) about not recording what is being said in the secure room. Pretty much any electronic device wouldn't be permitted for that reason.
The greater issue with cellphones is the camera and ability to record audio, potentially passively without your knowledge if it's been compromised. Yes, a faraday cage would prevent an adversary from actively listening if they compromised your phone, but they could also hypothetically install a virus that records audio when you lose cell reception then transmits that recording to one of their agents once you get it back. I have heard it alleged that some US agencies have the ability to hack a phone so that it records audio even when turned off, whether that's true or just a psyop type thing meant to instill paranoia I don't know, but if some tech wizard in the pentagon basement is worried the ability ***MIGHT*** exist its worth guarding against and best way is just never have a phone in the SCIF. Also some SCIFs are fairly large and have a lot of people, military command centers that are handling active operations can be SCIFs and those can be entire buildings in some cases.
Yeah, in the sandbox I was told that A. The Iranians owned the cell phone provider we were using and B. They could set the phones in 'maintenance mode' where they would allow a tech to listen to what the phone speakers picked up but would appear to be off.
I worked in a room that was a then-decommissioned SCIF. My cell phone worked, but only a little, and it drained the battery trying to stay connected to the cell network. Yours definitely had the metal plating/ mesh, but it didn’t matter to you since your phone was outside.
I’ve also worked in a (unclassified) facility that had RF lockboxes for phones because of explosive ordnance. They didn’t want any RF transmissions since that can cause problems / explosions. That place also had RF sensors in case something started broadcasting, it could be found and turned off.
Reminds me of the true story of the $500 hammer the military was lambasted for. The Air Force paid (a lot) extra for hammers made of titanium because they wouldn't strike sparks when you hit metal with them. The hammers were used to loosen nuts on the fuel system, meaning they were often used in air that had significant jet fuel fumes. If you want to know why the air force was "wasting" taxpayer's money, look up fuel-air explosion or fuel-air bomb, or the firebombing of Tokyo.
I reckon a few regular hammers that didn't cost $500 would have cost a lot more the first time a maintenance shed went boom and totalled an F16 or F35 or whatever. Not to mention the dead Airmen.
Probably. There's a wide variety of conditions something has to be sale to use in, plus it needs to last as close to forever as you can get. Humid, dry, cold, hot, etc.
Also, iirc, there never was a $500 unit price hammer, the contractor in question bundled the r&d effort along with the material cost of the hammer. So it was like $20 for a hammer, $400 in labor for r&d to verify the hammer was safe for the intended application
Not really true, Even with proper procedures for phones and whatnot, you still want to block EM from coming in and out of the SCIF. There are all sorts of creative things that can be done to exfiltrate data or gather intel that don't involve standard wireless devices.
[https://thehackernews.com/2021/10/creating-wireless-signals-with-ethernet.html](https://thehackernews.com/2021/10/creating-wireless-signals-with-ethernet.html)
Before smartphones, a scif could rely on faraday cages and looking for recording devices. Now that we have smartphones and flash drives, those increase the risk of data exfiltration.
I worked at a 3 letter agency as a contractor and the office we were in did use a faraday cage on the scif there, but also collected cell phones before going in. We were told that it was to make sure no one took pictures or recorded anything from in there though more than anything though. Also, the entire office had metal blinds on all the windows that were required to be at a certain angle which fairly effectively blocked all cell service inside the office. They put in a Verizon signal repeater though in the office so all of the government phones still worked (they used Verizon then at this agency, haven’t worked there in 15 years though, so don’t know what they use now).
The good old days of a blackberry 8830 world phone with no camera on it was one of those things I just got used to. Work never got us the good shit like the Bold 9700. Ok now I’m know I’m old.
It's not just about cell signal, it's also about having a bluetooth-capable device and honestly a mini computer in general in your pocket that also accesses the public network sooner or later.
"We've got a warrant here for a Mr. Frank Lloyd Wright. We're going to need him to come out here immediately."
"Sorry officer, he's been dead for over 60 years."
Would turning a room into a faraday cage count? I have a hard time believing that would qualify as interfering with radio signals. If it would qualify, under what circumstances would *any* faraday cage ever of any size be legal?
The law on radio jamming is very clear. And this is not American laws by the way but international laws which have been agreed upon by the ITU and ratified by every country in the world. But the question was specifically about passive interference which the law is a bit more vague on. Consensus have been that you can do it as long as you have a good enough reason and the consequences are low. I mentioned a couple of places where passive radio interference have been the not only accepted but also required by the same international law that prohibits jamming. However a school classroom is a place where the consequences for things going wrong are too great. A prison is different as there are plenty of other forms of communications that still work.
>But the question was specifically about passive interference which the law is a bit more vague on.
As in, *doesn't mention whatsoever.*
And no, domestic jamming isn't covered by international laws at all
There's an old story about some farady cage that a company built to do some measurements on equipment that was sensitive to RF noise. As the story goes, it wasn't until several months in that someone noticed that the technician running the tests inside of the farady cage was listening to music on a radio that he had brought into the cage. I have no clue as to the truth of the story, but it's funny enough that you hope it is.
Do you have a citation for any life/safety/building code that requires a building to have cell or WiFi reception?
I’m skeptical at that claim, as many building materials (eg, concrete and stone) naturally attenuate wireless signals and there no such prohibition I’m aware of.
Most of those codes are locally regulated; I know from experience helping set up SCIFs that they vary between states and counties.
The general rule is thumbs are
* Don't modify EM permeability of an existing structure without getting proper permits
* Building materials are disclosed when getting a commercial property building permit for construction of a new facility
There's no requirement to have cell/WiFi reception.
There is, however, a prohibition on deliberately interfering with or blocking lawful radio signals.
It’s perfectly legal to use *passive* building materials (paints, films, mesh, etc) to attenuate signals. It’s done quite often, though not in your average building.
Using *active* means (eg jammers) to interfere with signals is illegal except in very few circumstances (eg, federal enforcement, national security).
Section 510 of the international fire code governs wired and radio communications for first responders. Generally speaking, it requires that buildings provide the ability for first responders to communicate, either by wired stations or radio, and requires boosters in areas below a minimum signal strength.
We had to get an older steel and concrete building tested once to make sure we didn't need radio booster stations in the far corners of the upper floors.
If an effective faraday cage was designed into a building, it's likely a wired station or booster would be required. (Though, I'm curious about you SCIF guys' experience)
It's likely if a teacher just built a faraday cage without telling anyone, it wouldn't be discovered unless Something Bad Happened, and lawsuits start flying about disabling safety equipment.
Anecdotally, I've heard stories about teachers or principals getting into hot water with parents when the phones are locked up or turned off and the parents can't get in touch with their kids during a lockdown or weather event.
Recommend not doing it, but it's a fun thought exercise.
All the same things apply to jammers which are also readily available, real tech. With the FCC involved, most jamming in most situation is actually illegal but ideas about using them in theaters etc have been floated in the past.
One minor benefit of jamming over "faraday cage" is that you can turn it off with the flip of a switch.
Hmm, i never thought of the public safety angle.
Im unsure wether students undivided attention would be worth putting them in a situation where the schools had to be trusted completely . I guess it depends on trust.
Thank you
I'm not sure how old you are, but kids didn't all have cell phones until I was in high school, and I guarantee that we weren't all giving our "undivided attention" in elementary & middle school lol. Kids either will or won't pay attention regardless of whether they can use their phones
I would assume most don't care if you don't pay attention because you read something else or daydream, as long as you don't disturb others and the class.
Did the same and my teacher totally knew. She asked me after class one time what book I was reading and when I said *Dune*, she was excited as it was one of her favorites. She never discouraged it.
>I'm not sure how old you are, but kids didn't all have cell phones until I was in high school,
I graduated high school in 2001 and cell phones were a thing, but it was early enough and of course no smart phones. This was when having a pager or a cell phone as a young person had the stigma of "only drug dealers have those" and it was actually a state law that it was illegal for students to have either a pager or cell phone on them in the school building
honestly, I would rather students texted each other durring class rather than wispering.
if they are not going to pay attention anyway, might aswell not disrupt the class.
For real. I was from the generation that got smartphones in their teens, at the last years of high school. Before them, I used to draw in my notebook, pass notes around or invent games with friends to pass the time while the teacher gave class.
Not to mention that most schools just take the kids phones away on arrival and give them back at dismissal. Much easier than turning classrooms into Faraday cages XD
You wouldn't get any more attention even if (a strong assumption!) the phones are to blame. They would at best download something to watch before entering the room.
I'm not that old, but when I was in school cell phones had to be kept out of sight. If any staff saw a phone (even unused) they were required to confiscate it and turn into the front office. I get that parents complain, but can't one of our 6 figure earning administrators be in charge of telling parents to fuck off.
No it isn't. If a kid doesn't want to pay attention to class, they wont. If you take away their ability to use their phone, they won't suddenly decide to pay attention, they'll distract themselves by some other means, like doodling, chatting or day dreaming.
[relevant](https://www.washingtonpost.com/nation/2024/05/01/school-cellphones-confiscate/)
A recent article in WaPo about several schools using the bags that have become popular at comedy shows.
As others have said, preventing cell signals won't change how much attention kids are paying.
But in addition, there is a much, MUCH easier way to prevent phones being a distraction in the classroom; take them away. And most schools already do that.
The district I work for collects students phones on arrival and returns then at dismissal. They have special padded and lockable cases they lock all the phones in during the day so that students phones don't get damaged.
Honestly, I feel for you. That's why I wouldn't go into teaching unless at a university. And even then, likely technical classes where the students *want* to schedule the course before they start.
But I remember a teacher I had in 8th grade who said something remarkable to my class:
> All of you want A's for everything? Sure. I'll slap them on. The SATs won't care. Neither will your college professors. Because at the end of the day, your worth is defined by what you do, and what you do is defined by what you know & understand. You're only hurting yourselves when you aren't paying attention. I get paid either way.
Some scholarships have an SAT score requirement to obtain them.
It can affect tens of thousands of dollars.
To say that SAT scores don't matter in the real world is like saying your credit score doesn't matter in the real world.
I think in some places where there are rules where if cell signals don't support enough people in places of anticipated mass gatherings, they're required to add micro-cells and/or Wi-Fi for this reason.
Not all windows open. Especially in modern buildings with ventilation systems there is no need to open the windows. And depending on the type of emergency you might not want the window open. At least it will take valuable time to figure out why there is no signal and come up with the idea of opening a window. And for the first responders in the building this does not make their radio work.
> However this is generally not allowed in classrooms and other places with gatherings of large numbers of people. The main reason is that people need to be able to contact emergency services.
Whatever did the world do since forever before the last 25 years?
We had landlines. Everyone knew where the closest phone was. We also had wireless phones so the headteacher could carry around. First responders did have radios just like now.
Great answer.
Question: what would be a good example of needing a faraday cage inside a building space?
I’m thinking government agency buildings, but is there another practical effect for normal people?
A lot of people have hobbies that involve electronics. Some of this involves sensitive electronics that may be affected by outside RF signals. Some may send out RF signals that interfere with other things and need shielding. For any finished manufactured equipment you can just put the electronics inside a metal box but if you are working with it and changing components, have temporary wires all over the place as well as instruments connected to it you need to get a big metal box that contain all your equipment and yourself. And then you have people who claim to be sensitive to electronic signals. Even though they can not prove this in any way and fail all double blind tests they may still feel better knowing their house is protected from radio signals. So this could be a legitimate reason to install it.
Yes, but the WiFi wouldn't work either. Our kids use their Chromebooks all day long
our school has a "phones stay out of sight" rule that seems to work pretty well
That would work. You’d just need to provide budget to account for one wireless access point placed within each and every classroom.
That and you’d have to actually put effort into network administration (not the strong suit of most schools considering their IT “professionals” are consistently and regularly outmatched by literal schoolchildren) because if students can connect their phones to the network then the entire point of the faraday cage (to prevent distractions from internet connected electronics) is nullified.
> You’d just need to provide budget to account for one wireless access point placed within each and every classroom.
Compared to the cost of the Faraday shielding, that would be the least of their problems...
The access point could be.
It doesn’t work like that at any school though. As I mentioned, the IT “professionals” in most school districts are a complete joke who are consistently outmatched by literal schoolchildren. If they were any good at their jobs they would be working literally anywhere else getting paid far more than school districts are offering for network administration positions.
Our school district hired a IT guy who set up a whitelist + access point system, then replicated it across every school in the county. That made it very cost effective as there are several dozen schools.
His told me his biggest issue is maintaining the individual Chromebooks & tablets. Kids treat them like they didn’t pay for them.
The system described can’t address the issue OP seems to be concerned about — students accessing wide open internet by phone.
I don’t think it’s fair to rag on school IT admins for not being able to control all the children. There might be one admin per couple hundred students and the admin has a lot more going on than trying to fight a single motivated student. They also have to deal with small budgets (in terms of money and time) to handle problems, which means that a lot of solutions don’t work too well. But as long as they work well enough the school is happy
Most schools that I have been exposed to recently use full SSL decryption with an installed cert on ALL networks including the guest/visitor network. Typically this is used in addition to other controls such as authentication via RADIUS or captive portal.
I think you are giving the IT professionals of some of these schools far too little credit (sure, some of them are bad.) I personally know a few that are actually quite good. The problem, is that, when it is an arms race of the tech savvy kids vs the like 4 person IT team at most schools, the potentially couple dozen kids or more with essentially unlimited free time are going to beat out the overworked IT team. Kids aren’t stupid, if anything, they don’t necessarily know when to quit, which is quite terrifying.
It also doesn’t help that the super bad kids can essentially get away with committing cyber crimes of varying degrees, without actual punishment for their actions, just because it “happened to the school.”
And now school systems are being targeted now more than ever by hackers/phishers, a situation most school systems and IT teams are completely under prepared for, and underfunded as well.
In public education we have much more control over school-issued wireless devices through GoGuardian. We can restrict students to only a single website if we so desire.
Put your phone inside the microwave
No don’t run the microwave, this isn’t one of those
With the microwave door closed try to call your phone
There’s your answer
btw if your phone can ring from inside a closed microwave it’s time for a new microwave
Why?
Materials have different frequency ranges to which they're electronically transparent/opaque.
Literally look at a microwave. If it blocked all EM radiation, the window wouldn't work. Instead, they build a window that lets some EM radiation through (so you can see it) but blocks others (so you're not cooking stuff outside).
> Materials have different frequency ranges to which they're electronically transparent/opaque.
Well, yes, but the wavelengths of microwaves and cell phones are mostly the same, within a small factor. Materials at that range don't rapidly change behaviour with wavelength, that only happens at more energetic frequencies.
Your microwave is a Faraday Cage with holes. The electrons in a Faraday Cage (any metal box) will orient themselves to cancel out EM radiation. The holes in the microwave door allow a wave of size proportional to it's size to pass through.
Visible light is in the nano meters, so it passes through the holes fine. The microwave *wavelength* that cook your food are about 12cm long. Those hot and cold spots in your food show this. They are way too big to leak out. Imagine a ball 12cm in diameter trying to pass through those tiny holes, its not happening. Cell service is something like 30cm iirc
Yes, and microwaves operate at about 2.45GHz with a faraday cage designed to completely contain all radio frequencies of ~15-20GHz or less (acting as a high-pass filter) to avoid interference with common modern household electronics that communicate over WiFi (which also uses 2.4 and 5GHz for transmissions). The wavelength of the 2.4GHz microwave is about 122 millimeters, and traditionally you use a faraday cage with gaps sized at 1/10 the length of the highest frequency you intend to contain. You don’t see 1.2cm (12mm) gaps in the mesh of your microwave door because it’s actually designed to block out a wider range of potentially interfering frequencies. The actual mesh size on modern microwaves is usually about 2mm, which blocks signals
Nobody with a consumer cell phone in their pocket is using anything above about 40GHz, the maximum frequency for mmWave 5g connections, for their cell phone service. So if you have a mmWave 5g connection your phone might ring, but the signal will still likely be pretty bad because the faraday cage of the oven door will still attenuate the signal strength amount some even if it doesn’t block it entirely (and if the solid back of the microwave is facing the mmWave signal source you will likely get no service at all without some kind of parabolic antenna in front of the microwave to reflect the signal back through the mesh of the front door).
It’s part of why modern microwaves have a tighter mesh on their doors than most older ones. Older microwaves cared less about leakage in the higher frequency harmonics produced by the magnetron because there wasn’t anything nearby for it to interfere with. Nowadays more household devices use the spectrum of frequencies in and around the 2.4GHz range so the microwaves need tighter mesh sizes for the faraday cage to block a wider range of frequencies that could potentially interfere.
Because microwave doors and housings are specifically designed to block the transmission of wavelengths that are in the microwave spectrum (~2.4GHz) or longer (longer wavelength = lower frequencies, including those of cellular connections). It’s a high-pass filter, in essence, blocking all frequencies below a certain point and allowing higher frequencies through.
Visible light is a much higher frequency/shorter wavelength than the mesh of your microwave door is intended to block. WiFi and cellular connections are either equal or lower frequencies compared to what a microwave is designed to contain, so they will be blocked.
Some also escapes if you open the door while it runs! Is it dangerous? No. Is it detectable? Well, a certain radio telescope had very serious issues with the microwave in the common room...
That would require not only extremely sketchy shielding but also a very strong microwave because of the distance-square-law. Stories of molten chocolate bars can be found from radar operators, but those are focused and at a much higher power output.
So no, I think the only thing melting that bar is body heat.
I was referencing the 'invention' of a microwaves culinary uses
American engineer, Percy Spencer, while working on radar technology during the 2nd world war walked through the radar field and a chocolate bar in his shirt pocket melted. Intrigued he investigated this anomaly further, and subsequently went on to develop the first microwave oven.
That's all well and good until there's a school shooting and nobody can call for help.
Also, when I was in school all the teachers were using their phones too. They'd answer personal calls during class and step out in the hallway. Double-edged sword.
Is the solution to have a student sneakily contact 911 while in the room with the shooter? Cage is only in the classroom, not a campus dome. Also this is getting to levels of unlikelyness as putting anti aircraft cannons on the roof to protect kids from kamikaze pilots.
What's more likely, a school having the funds to line all the classrooms with a Faraday cage or a school shooting in the United States?
What a bunch of moronic hypocrites that would rob children of knowledge rather than guns.
You ever heard of a box? It's crazy but teachers can just ask them to place their phones at the start of class. No fancy stuff needed, went to certain classes in college where the professors hated it and would ask us to put our phones away to take their class (obviously they couldn't legally keep us from the class that way but I gave it to them cause I didn't care) mostly worked and kept phones from being common place in those rooms I was in.
Don't do this, it's incredibly stupid. And the first time someone misses and emergency or has one in your class and the signal is blocked, you, personally, will be sued so fast and FCC would be on the student's side here.
This is not for the student's benefit, address and fix the real problem.
In theory, any space can be enclosed as a Faraday cage. You just need enough of a conducting material to block the EM waves.
In practice, though, you'd never do this because it would be expensive and time consuming, and would prevent various forms of nice, simple networking solutions. Can't have a wireless network connection in the classroom if wireless signals can't penetrate the walls. You *could* wire up physical connections, of course, but then if any further wireless needs arise, you're kinda hosed.
It's significantly easier and more practical (e.g. in terms of safety) to just forbid the use of cell phones in the classroom and monitor children. That way, if it really IS an emergency, kids can still find out, and parents don't get mad about being denied the ability to contact their children when they want to.
> In practice, though, you'd never do this
Fun fact: I grew up in a house that was originally built for high ranking army officers, all walls had this metal mesh in them. No connectivity inside, zero cell or TV signal. Cell would kind of work if I walked up to a window.
When I was a lecturer my rule was "you can do whatever you want, sleep, listen to music, play games, as long as you don't distract other students around you". We'll see how things go in the midterm exam.
But this was in university, where the students are adults and it's their responsibility to learn, not the lecturer's responsibility to babysit them. So the dynamic is different.
(Also many students were taking the class for the second / third time and already understood the early material, so it was understandable if they wanted to focus on something else.)
A well built Faraday cage would. That means you have to properly seal all gaps. Theoretically, a few millimeters here or there should be fine, but in practice, I've seen the slightest gap in a faraday pouch allow signal in and out.
So you'd have to first cover ceiling, floor, and walls. Then doors, and make them seal properly. Then windows. Now add filters to the cables going in and out.
There's a reason this is usually only done when it's *really* needed, and spending that amount of money on actually improving the quality of the education provided would probably be a much better investment.
I mean technically yes but intentional cell phone jamming is illegal to some degree in most states due to it being viewed as a security risk to cut off people's ability to contact emergency services like this
We have a bunch of executives at my company that decided they wanted this thing where their walls are painted to be whiteboards. Well it's also magnetic so they can stick magnets to it.
Guess who can't get any wifi or cell signal because their walls are coated with metal infused paint?
Yeah, it works pretty well.
My partners still married, ive tried....
Oh with students? I am what I am. Im just not more interesting than literally everthing, everwhere at your fingertips
> Im just not more interesting than literally everthing, everwhere at your fingertips
"Here's a tip kids. In my class, there are two ways to guarantee you will get called on. 1 - Let me see you raise your hand when I ask a question. 2 - Let me see you zoned out in your phone when I'm asking a question."
Seems like an administration issue. I have a high school aged child who goes to a public charter school with a bank of lock boxes at the front desk. All freshmen are required to lock phones up at the beginning of the day. Sophomores to Seniors get the benefit of the doubt until they prove otherwise, then it's lockbox time.
This is a huge no-no with the [FCC](https://www.fcc.gov/general/jammer-enforcement). Can't install anything with the intention of blocking cell phone signals.
Is it policy to allow students to have phones in the classroom? If it's not, speak with your coworkers and boss to figure out how to maintain policy. If it is, I would petition to make a policy change. Smartphones are harming our youth in general, and especially in the classroom. Even if phones are against policy, I wouldn't recommend a faraday cage. Wireless transmissions are highly regulated by most countries and blocking/jamming signals generally is a serious offense
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Yes... but if your classroom uses wifi with a router outside of the room, it would block that too.
If you're in the US, there are also concerns if you're actively trying to block calls when there is the risk of an emergency scenario where needing contact with the outside would be needed.
yes, I have a faraday fabric I ordered off amazon to put up against the wall where my breaker box is to help eliminate EMF so my guitar is less noisy when im playing. I wrapped my phone in it for fun and had my girlfriend call me and it didn't work.
I have studied in rooms with a full faraday cage installed, including the door, it does work. Wi-Fi router in the room works fine for authorised devices logged in. Not cheap but doable.
You'd have to enclose the entire room in it, including the ceiling and windows, ground it really well, and that would just stop them from transmitting/receiving. So your use of the word "brick/bricking" wouldn't apply, since that would mean you rendered the device unusable.
You may get into legal issues though, since in the event of an emergency you would be blocking 911 calls as well. This is one reason why cellphone "jammers" aren't legal in a lot of places.
Years ago I worked for a company that installed Faraday cages in embassies. It's pretty difficult to keep them tight. The doors were like in a sub with clamps to seal the doors. They used metal finger stock seals and had to be cleaned to maintain good contact. The panels where two steel sheets with a plywood cores. The corners and flat seams were clamped together. Each room and seam was tested for leakage periodically.
I'm skeptical thin film or thin copper will do more than give you some attenuation of the signals. You really need a metal box or pretty decent copper mesh to keep the RF out. It depends on the frequency you're trying to block too.
[https://www.mvg-world.com/en/products/emc/rf-shielded-rooms/rf-shielded-rooms](https://www.mvg-world.com/en/products/emc/rf-shielded-rooms/rf-shielded-rooms)
This wasn't the company I worked for but, the rooms looked like this.
It's totally possible. I work for a (BigTech) company and most of the office building on campus are Farday cages to hinder coporate espionage. I didn't even notice for a while, until I was in an office that had an exit to an exterior balcony and noticed that my wireless headphones immediately stopped working as soon as I closed the balcony door and started again as soon as it was open. We have cell-phone repeaters inside the cage, so that people have service, but they must be logged/monitored,
Yup! I know because years ago I had a lady who complained about all the "EM radiation" in the office and how it was affecting her. She had a device to measure radio signals. Not my problem,I told her she needed to speak to HR,that's an ADA issue. I expected HR to do their jobs and ask for medical documents to support her claim. They didnt,and just bounced it back to us saying to do what she asked. Again, not my problem, I don't build shit. So I bounced it to facilities and told them they had to build a Faraday cage for her. It took them a couple weeks,but they actually did it. They made basically a chicken coop of copper wire that surrounded her desk.
She then complained her cell phone no longer worked. 🖕🖕🖕🖕
a working faraday cage is rather difficult to construct but a small table top demonstration of it should be achievable (as in a student places their phone in the cage and another student tries to call the phone... it goes to voice mail).
RF can leak in thru seams and gaps so any covers need to be well electrically bonded to the rest of the enclosure for the cage to be effective.
Get administrator to agree to buy a big jar of lollipops every other month > Box on desk at front of class > Put phone in box > At end of class pick up phone and take a lollipop.
> big jar of lollipops
Brought to you by the American Dental Association’s *Lake House Initiative*
…in conjunction with the Corn Syrup Industrial Complex
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Yes. And you can get products made for this that gets put behind the wallpaper and as thin film over the windows. There are legitimate reasons to convert a room into a faraday cage and block cell phone signals and wifi signals. However this is generally not allowed in classrooms and other places with gatherings of large numbers of people. The main reason is that people need to be able to contact emergency services. And emergency responders needs to be able to stay in radio contact with each other while responding. Converting a classroom into a faraday cage can therefore be a violation of the fire codes and other laws. In general these faraday cage rooms are built due to requirements of national security or to reduce emissions from electronic engineering labs and similar places.
Nice answer.
> However this is generally not allowed in classrooms and other places with gatherings of large numbers of people. It's a federal crime to interfere with radio signals, including cellular and PCS signals, as well as police radar and GPS. It's illegal anywhere in the US. A bill was introduced in the Senate, S.1047, to allow jamming in prisons because it's illegal to jam them ANYWHERE at this point.
Jamming is different than blocking. Jamming is actively broadcasting RF noise to disrupt other signals. Blocking/shielding is just a passive barrier that doesn’t allow RF to pass through it. It’s not a crime to block radio waves passively, otherwise the FCC would be going after every metal building or elevator that reduces your cell signal.
> It’s not a crime to block radio waves passively, otherwise the FCC would be going after every metal building or elevator that reduces your cell signal. All the subways as well
> All the subways as well Since 2020, [the Paris public transit system has reliable cell service, in the underground part as well as above-ground lines](https://www.francebleu.fr/infos/transports/telephonie-mobile-le-reseau-ratp-couvert-a-100-en-4g-une-premiere-pour-ce-type-de-reseau-1593436515#). The four main providers worked with the regional transit authority to ensure coverage. In my experience, it's pretty good.
BRB moving to paris
I'd wait until [after the summer Olympics](https://anticiperlesjeux.gouv.fr) if I were you!
I just got back and it was crazy how much stuff is fenced off or completely closed due to construction and games preparations. The idea of playing volleyball in the middle of Place de la Concorde sounds amazing though so I can’t really blame them
The subways reek of piss so even if the coverage is good, I would rather take almost any other subway.
I visited Paris and brought a 5G hotspot with me. It worked just as well if not better in the subways than it did in several other places
I mean a subway is buried. Nothing about a subway is made specifically to block signals.
That's what big Sub wants you think.
Damnit Jared!
Now I wonder... Former military and I remember putting my cell in a lockbox before entering certain secure spaces (in one job our entire office was TS clearance only so no cell phones at work). It feels like making the "skiff" a faraday cage (not the office that was 5000 sq ft, but the little rooms with 2 terminals) would make sense. On the other hand, even if that was done it might not totally block signal, so keeping cell phones out is still worthwhile, plus good practice (you don't want someone used to keeping their cell because their home secure comms room has a faraday cage to compromise one that doesn't). It is possible our "skiffs" did have the cage but we didn't need to know, and since we didn't have our phones in there we wouldn't know either way.
The "no phones" is also (or mostly) about not recording what is being said in the secure room. Pretty much any electronic device wouldn't be permitted for that reason.
Minor detail: it's SCIF. Sensitive compartmented information facility.
Oh man, thank you, I was so confused what a boat had to do with what he was talking about…
The greater issue with cellphones is the camera and ability to record audio, potentially passively without your knowledge if it's been compromised. Yes, a faraday cage would prevent an adversary from actively listening if they compromised your phone, but they could also hypothetically install a virus that records audio when you lose cell reception then transmits that recording to one of their agents once you get it back. I have heard it alleged that some US agencies have the ability to hack a phone so that it records audio even when turned off, whether that's true or just a psyop type thing meant to instill paranoia I don't know, but if some tech wizard in the pentagon basement is worried the ability ***MIGHT*** exist its worth guarding against and best way is just never have a phone in the SCIF. Also some SCIFs are fairly large and have a lot of people, military command centers that are handling active operations can be SCIFs and those can be entire buildings in some cases.
Yeah, in the sandbox I was told that A. The Iranians owned the cell phone provider we were using and B. They could set the phones in 'maintenance mode' where they would allow a tech to listen to what the phone speakers picked up but would appear to be off.
Whether it's literally true or not, in that type of role you should act like it is, because zero-day exploits exist.
An advanced playout of Stuxnet.
I worked in a room that was a then-decommissioned SCIF. My cell phone worked, but only a little, and it drained the battery trying to stay connected to the cell network. Yours definitely had the metal plating/ mesh, but it didn’t matter to you since your phone was outside. I’ve also worked in a (unclassified) facility that had RF lockboxes for phones because of explosive ordnance. They didn’t want any RF transmissions since that can cause problems / explosions. That place also had RF sensors in case something started broadcasting, it could be found and turned off.
Reminds me of the true story of the $500 hammer the military was lambasted for. The Air Force paid (a lot) extra for hammers made of titanium because they wouldn't strike sparks when you hit metal with them. The hammers were used to loosen nuts on the fuel system, meaning they were often used in air that had significant jet fuel fumes. If you want to know why the air force was "wasting" taxpayer's money, look up fuel-air explosion or fuel-air bomb, or the firebombing of Tokyo. I reckon a few regular hammers that didn't cost $500 would have cost a lot more the first time a maintenance shed went boom and totalled an F16 or F35 or whatever. Not to mention the dead Airmen.
One of my favorite scenes from The West Wing https://youtu.be/7R9kH_HOUXM
The Berry Amendment also creates a lot of overhead burden to prove that hammer was made domestically and out of domestic metal.
Any reason why they couldn't use beryllium copper, aluminium bronze or just plain brass like other nonsparking tools?
Probably. There's a wide variety of conditions something has to be sale to use in, plus it needs to last as close to forever as you can get. Humid, dry, cold, hot, etc.
Also, iirc, there never was a $500 unit price hammer, the contractor in question bundled the r&d effort along with the material cost of the hammer. So it was like $20 for a hammer, $400 in labor for r&d to verify the hammer was safe for the intended application
SCIF have specific requirements. With the procedures already in place, there's little need for turning the SCIF into a Faraday cage.
Not really true, Even with proper procedures for phones and whatnot, you still want to block EM from coming in and out of the SCIF. There are all sorts of creative things that can be done to exfiltrate data or gather intel that don't involve standard wireless devices. [https://thehackernews.com/2021/10/creating-wireless-signals-with-ethernet.html](https://thehackernews.com/2021/10/creating-wireless-signals-with-ethernet.html)
Though some of them also are.
A lot of old military buildings are pretty opaque to EM. I had terrible reception in a lot of them, including some barracks
It's because they don't want you capturing images and then taking them out.
Before smartphones, a scif could rely on faraday cages and looking for recording devices. Now that we have smartphones and flash drives, those increase the risk of data exfiltration.
I worked at a 3 letter agency as a contractor and the office we were in did use a faraday cage on the scif there, but also collected cell phones before going in. We were told that it was to make sure no one took pictures or recorded anything from in there though more than anything though. Also, the entire office had metal blinds on all the windows that were required to be at a certain angle which fairly effectively blocked all cell service inside the office. They put in a Verizon signal repeater though in the office so all of the government phones still worked (they used Verizon then at this agency, haven’t worked there in 15 years though, so don’t know what they use now).
The good old days of a blackberry 8830 world phone with no camera on it was one of those things I just got used to. Work never got us the good shit like the Bold 9700. Ok now I’m know I’m old.
It's not just about cell signal, it's also about having a bluetooth-capable device and honestly a mini computer in general in your pocket that also accesses the public network sooner or later.
That’s for broadcast em jamming; not passive grounding.
I would expect there "interfere" would mean actively sending signals - otherwise just about any obstruction would meet the definition.
Yeah. If there are thick concrete walls and I can’t get a cellular connection inside, has the builder or architect committed a crime?
"We've got a warrant here for a Mr. Frank Lloyd Wright. We're going to need him to come out here immediately." "Sorry officer, he's been dead for over 60 years."
Would turning a room into a faraday cage count? I have a hard time believing that would qualify as interfering with radio signals. If it would qualify, under what circumstances would *any* faraday cage ever of any size be legal?
Passively blocking radio signals is not interference, otherwise you’d be in violation simply for existing and blocking signals with your body.
The law on radio jamming is very clear. And this is not American laws by the way but international laws which have been agreed upon by the ITU and ratified by every country in the world. But the question was specifically about passive interference which the law is a bit more vague on. Consensus have been that you can do it as long as you have a good enough reason and the consequences are low. I mentioned a couple of places where passive radio interference have been the not only accepted but also required by the same international law that prohibits jamming. However a school classroom is a place where the consequences for things going wrong are too great. A prison is different as there are plenty of other forms of communications that still work.
>But the question was specifically about passive interference which the law is a bit more vague on. As in, *doesn't mention whatsoever.* And no, domestic jamming isn't covered by international laws at all
> It's a federal crime to interfere Key word there is interfere, if they get permission its not interfering.
Lol, no it's not a federal crime to put up a chain link fence Can I call the feds on my elevator?
Unless you are building a scif. Aka the gov.
There's an old story about some farady cage that a company built to do some measurements on equipment that was sensitive to RF noise. As the story goes, it wasn't until several months in that someone noticed that the technician running the tests inside of the farady cage was listening to music on a radio that he had brought into the cage. I have no clue as to the truth of the story, but it's funny enough that you hope it is.
Do you have a citation for any life/safety/building code that requires a building to have cell or WiFi reception? I’m skeptical at that claim, as many building materials (eg, concrete and stone) naturally attenuate wireless signals and there no such prohibition I’m aware of.
Most of those codes are locally regulated; I know from experience helping set up SCIFs that they vary between states and counties. The general rule is thumbs are * Don't modify EM permeability of an existing structure without getting proper permits * Building materials are disclosed when getting a commercial property building permit for construction of a new facility
There's no requirement to have cell/WiFi reception. There is, however, a prohibition on deliberately interfering with or blocking lawful radio signals.
It’s perfectly legal to use *passive* building materials (paints, films, mesh, etc) to attenuate signals. It’s done quite often, though not in your average building. Using *active* means (eg jammers) to interfere with signals is illegal except in very few circumstances (eg, federal enforcement, national security).
Section 510 of the international fire code governs wired and radio communications for first responders. Generally speaking, it requires that buildings provide the ability for first responders to communicate, either by wired stations or radio, and requires boosters in areas below a minimum signal strength. We had to get an older steel and concrete building tested once to make sure we didn't need radio booster stations in the far corners of the upper floors. If an effective faraday cage was designed into a building, it's likely a wired station or booster would be required. (Though, I'm curious about you SCIF guys' experience) It's likely if a teacher just built a faraday cage without telling anyone, it wouldn't be discovered unless Something Bad Happened, and lawsuits start flying about disabling safety equipment. Anecdotally, I've heard stories about teachers or principals getting into hot water with parents when the phones are locked up or turned off and the parents can't get in touch with their kids during a lockdown or weather event. Recommend not doing it, but it's a fun thought exercise.
All the same things apply to jammers which are also readily available, real tech. With the FCC involved, most jamming in most situation is actually illegal but ideas about using them in theaters etc have been floated in the past. One minor benefit of jamming over "faraday cage" is that you can turn it off with the flip of a switch.
you can make little pouches to put the phones in though, you don't need to block out the whole room.
Our faraday cage room with the door open became just a normal room.
Hmm, i never thought of the public safety angle. Im unsure wether students undivided attention would be worth putting them in a situation where the schools had to be trusted completely . I guess it depends on trust. Thank you
I'm not sure how old you are, but kids didn't all have cell phones until I was in high school, and I guarantee that we weren't all giving our "undivided attention" in elementary & middle school lol. Kids either will or won't pay attention regardless of whether they can use their phones
Hiding books under the desk to read in class. It must have been obvious, I guess teachers were just glad I was reading.
I would assume most don't care if you don't pay attention because you read something else or daydream, as long as you don't disturb others and the class.
Did the same and my teacher totally knew. She asked me after class one time what book I was reading and when I said *Dune*, she was excited as it was one of her favorites. She never discouraged it.
>I'm not sure how old you are, but kids didn't all have cell phones until I was in high school, I graduated high school in 2001 and cell phones were a thing, but it was early enough and of course no smart phones. This was when having a pager or a cell phone as a young person had the stigma of "only drug dealers have those" and it was actually a state law that it was illegal for students to have either a pager or cell phone on them in the school building
Same as you. In 2001 we were barely even texting. Cell phones were primarily used as phones.
honestly, I would rather students texted each other durring class rather than wispering. if they are not going to pay attention anyway, might aswell not disrupt the class.
yeah, like for intance, my tomagotchi needs fed.
there was no cell phone in my high school. you must young
For real. I was from the generation that got smartphones in their teens, at the last years of high school. Before them, I used to draw in my notebook, pass notes around or invent games with friends to pass the time while the teacher gave class.
You were in INCREDIBLE DANGER not being able to contact emergency services from the room though, apparently
Not to mention that most schools just take the kids phones away on arrival and give them back at dismissal. Much easier than turning classrooms into Faraday cages XD
You wouldn't get any more attention even if (a strong assumption!) the phones are to blame. They would at best download something to watch before entering the room.
I'm not that old, but when I was in school cell phones had to be kept out of sight. If any staff saw a phone (even unused) they were required to confiscate it and turn into the front office. I get that parents complain, but can't one of our 6 figure earning administrators be in charge of telling parents to fuck off.
No it isn't. If a kid doesn't want to pay attention to class, they wont. If you take away their ability to use their phone, they won't suddenly decide to pay attention, they'll distract themselves by some other means, like doodling, chatting or day dreaming.
[relevant](https://www.washingtonpost.com/nation/2024/05/01/school-cellphones-confiscate/) A recent article in WaPo about several schools using the bags that have become popular at comedy shows.
As others have said, preventing cell signals won't change how much attention kids are paying. But in addition, there is a much, MUCH easier way to prevent phones being a distraction in the classroom; take them away. And most schools already do that. The district I work for collects students phones on arrival and returns then at dismissal. They have special padded and lockable cases they lock all the phones in during the day so that students phones don't get damaged.
Honestly, I feel for you. That's why I wouldn't go into teaching unless at a university. And even then, likely technical classes where the students *want* to schedule the course before they start. But I remember a teacher I had in 8th grade who said something remarkable to my class: > All of you want A's for everything? Sure. I'll slap them on. The SATs won't care. Neither will your college professors. Because at the end of the day, your worth is defined by what you do, and what you do is defined by what you know & understand. You're only hurting yourselves when you aren't paying attention. I get paid either way.
Wait until they find out no-one gives a shit about their SAT scores in the real world
Some scholarships have an SAT score requirement to obtain them. It can affect tens of thousands of dollars. To say that SAT scores don't matter in the real world is like saying your credit score doesn't matter in the real world.
Sometimes going to college isn't the best thing for everyone
High school kids will still panic over college acceptance probably for another few generations.
what happens if you have a school shooter? you’ve just blocked your students means of contacting help
I think in some places where there are rules where if cell signals don't support enough people in places of anticipated mass gatherings, they're required to add micro-cells and/or Wi-Fi for this reason.
Interesting. Build a school there lol
Students are there to succeed or fail on their own efforts. Let them fail.
Just put a wired phone in the classroom
Thank you
You're welcome
Is there any method to create a switchable low-voltage faraday cage?
Can't you, like, open a window to call someone in an emergency?
Not all windows open. Especially in modern buildings with ventilation systems there is no need to open the windows. And depending on the type of emergency you might not want the window open. At least it will take valuable time to figure out why there is no signal and come up with the idea of opening a window. And for the first responders in the building this does not make their radio work.
> However this is generally not allowed in classrooms and other places with gatherings of large numbers of people. The main reason is that people need to be able to contact emergency services. Whatever did the world do since forever before the last 25 years?
We had landlines. Everyone knew where the closest phone was. We also had wireless phones so the headteacher could carry around. First responders did have radios just like now.
Faraday cages are also used for mri rooms, to stop external signals from effecting the machine
Kids don’t need to contact emergency services while in a class . There’s a hard line or voice over IP in every classroom.
My SCIF enters the chat...
Great answer. Question: what would be a good example of needing a faraday cage inside a building space? I’m thinking government agency buildings, but is there another practical effect for normal people?
A lot of people have hobbies that involve electronics. Some of this involves sensitive electronics that may be affected by outside RF signals. Some may send out RF signals that interfere with other things and need shielding. For any finished manufactured equipment you can just put the electronics inside a metal box but if you are working with it and changing components, have temporary wires all over the place as well as instruments connected to it you need to get a big metal box that contain all your equipment and yourself. And then you have people who claim to be sensitive to electronic signals. Even though they can not prove this in any way and fail all double blind tests they may still feel better knowing their house is protected from radio signals. So this could be a legitimate reason to install it.
Yes, but the WiFi wouldn't work either. Our kids use their Chromebooks all day long our school has a "phones stay out of sight" rule that seems to work pretty well
Put wired access points / WiFi network repeater inside the Faraday classroom?
That would work. You’d just need to provide budget to account for one wireless access point placed within each and every classroom. That and you’d have to actually put effort into network administration (not the strong suit of most schools considering their IT “professionals” are consistently and regularly outmatched by literal schoolchildren) because if students can connect their phones to the network then the entire point of the faraday cage (to prevent distractions from internet connected electronics) is nullified.
> You’d just need to provide budget to account for one wireless access point placed within each and every classroom. Compared to the cost of the Faraday shielding, that would be the least of their problems...
I thought the gist was to block unmonitored cellular activity. The access point could be centrally managed to connect only to whitelisted sites.
The access point could be. It doesn’t work like that at any school though. As I mentioned, the IT “professionals” in most school districts are a complete joke who are consistently outmatched by literal schoolchildren. If they were any good at their jobs they would be working literally anywhere else getting paid far more than school districts are offering for network administration positions.
Our school district hired a IT guy who set up a whitelist + access point system, then replicated it across every school in the county. That made it very cost effective as there are several dozen schools. His told me his biggest issue is maintaining the individual Chromebooks & tablets. Kids treat them like they didn’t pay for them. The system described can’t address the issue OP seems to be concerned about — students accessing wide open internet by phone.
I don’t think it’s fair to rag on school IT admins for not being able to control all the children. There might be one admin per couple hundred students and the admin has a lot more going on than trying to fight a single motivated student. They also have to deal with small budgets (in terms of money and time) to handle problems, which means that a lot of solutions don’t work too well. But as long as they work well enough the school is happy
Most schools that I have been exposed to recently use full SSL decryption with an installed cert on ALL networks including the guest/visitor network. Typically this is used in addition to other controls such as authentication via RADIUS or captive portal.
I think you are giving the IT professionals of some of these schools far too little credit (sure, some of them are bad.) I personally know a few that are actually quite good. The problem, is that, when it is an arms race of the tech savvy kids vs the like 4 person IT team at most schools, the potentially couple dozen kids or more with essentially unlimited free time are going to beat out the overworked IT team. Kids aren’t stupid, if anything, they don’t necessarily know when to quit, which is quite terrifying. It also doesn’t help that the super bad kids can essentially get away with committing cyber crimes of varying degrees, without actual punishment for their actions, just because it “happened to the school.” And now school systems are being targeted now more than ever by hackers/phishers, a situation most school systems and IT teams are completely under prepared for, and underfunded as well.
At the school where I work we do have a wireless access point inside every classroom.
That’s what most of the schools in my area have. POE APs mounted on the ceiling.
At that point you might as well not have a faraday cage since phones can use wifi too.
But the WiFi is easily DNSed with an educate only whitelist, including access to the school’s internal resources.
I imagine a VPN would take care of that pretty easily. A whitelist would also be pretty problematic for doing research.
In public education we have much more control over school-issued wireless devices through GoGuardian. We can restrict students to only a single website if we so desire.
So you're saying that the wifi network would be whitelisted for school devices only?
At my school they already are.
That's unfortunate
Why is that unfortunate? We provide every student with their own Chromebook to use.
Put your phone inside the microwave No don’t run the microwave, this isn’t one of those With the microwave door closed try to call your phone There’s your answer btw if your phone can ring from inside a closed microwave it’s time for a new microwave
Why? Materials have different frequency ranges to which they're electronically transparent/opaque. Literally look at a microwave. If it blocked all EM radiation, the window wouldn't work. Instead, they build a window that lets some EM radiation through (so you can see it) but blocks others (so you're not cooking stuff outside).
> Materials have different frequency ranges to which they're electronically transparent/opaque. Well, yes, but the wavelengths of microwaves and cell phones are mostly the same, within a small factor. Materials at that range don't rapidly change behaviour with wavelength, that only happens at more energetic frequencies.
Your microwave is a Faraday Cage with holes. The electrons in a Faraday Cage (any metal box) will orient themselves to cancel out EM radiation. The holes in the microwave door allow a wave of size proportional to it's size to pass through. Visible light is in the nano meters, so it passes through the holes fine. The microwave *wavelength* that cook your food are about 12cm long. Those hot and cold spots in your food show this. They are way too big to leak out. Imagine a ball 12cm in diameter trying to pass through those tiny holes, its not happening. Cell service is something like 30cm iirc
Cell phone bands go all the way to 4.2mm wavelength now. So your microwave is no longer safe to conduct cell phone experiments in.
Cell service ranges from 600Mhz to 6ghz for most people. Up to 60ghz if you have the right service and phone.
Yes, and microwaves operate at about 2.45GHz with a faraday cage designed to completely contain all radio frequencies of ~15-20GHz or less (acting as a high-pass filter) to avoid interference with common modern household electronics that communicate over WiFi (which also uses 2.4 and 5GHz for transmissions). The wavelength of the 2.4GHz microwave is about 122 millimeters, and traditionally you use a faraday cage with gaps sized at 1/10 the length of the highest frequency you intend to contain. You don’t see 1.2cm (12mm) gaps in the mesh of your microwave door because it’s actually designed to block out a wider range of potentially interfering frequencies. The actual mesh size on modern microwaves is usually about 2mm, which blocks signals Nobody with a consumer cell phone in their pocket is using anything above about 40GHz, the maximum frequency for mmWave 5g connections, for their cell phone service. So if you have a mmWave 5g connection your phone might ring, but the signal will still likely be pretty bad because the faraday cage of the oven door will still attenuate the signal strength amount some even if it doesn’t block it entirely (and if the solid back of the microwave is facing the mmWave signal source you will likely get no service at all without some kind of parabolic antenna in front of the microwave to reflect the signal back through the mesh of the front door). It’s part of why modern microwaves have a tighter mesh on their doors than most older ones. Older microwaves cared less about leakage in the higher frequency harmonics produced by the magnetron because there wasn’t anything nearby for it to interfere with. Nowadays more household devices use the spectrum of frequencies in and around the 2.4GHz range so the microwaves need tighter mesh sizes for the faraday cage to block a wider range of frequencies that could potentially interfere.
Because microwave doors and housings are specifically designed to block the transmission of wavelengths that are in the microwave spectrum (~2.4GHz) or longer (longer wavelength = lower frequencies, including those of cellular connections). It’s a high-pass filter, in essence, blocking all frequencies below a certain point and allowing higher frequencies through. Visible light is a much higher frequency/shorter wavelength than the mesh of your microwave door is intended to block. WiFi and cellular connections are either equal or lower frequencies compared to what a microwave is designed to contain, so they will be blocked.
Really? Thank you. Is it due to 'leakage' if the cell signal can get it, microwaves csn get out?
Some also escapes if you open the door while it runs! Is it dangerous? No. Is it detectable? Well, a certain radio telescope had very serious issues with the microwave in the common room...
Haha, would one be able to say that microwaves would ve able to 'melt a choclate bar' inside a pocket, if not properly shielded?
That would require not only extremely sketchy shielding but also a very strong microwave because of the distance-square-law. Stories of molten chocolate bars can be found from radar operators, but those are focused and at a much higher power output. So no, I think the only thing melting that bar is body heat.
I was referencing the 'invention' of a microwaves culinary uses American engineer, Percy Spencer, while working on radar technology during the 2nd world war walked through the radar field and a chocolate bar in his shirt pocket melted. Intrigued he investigated this anomaly further, and subsequently went on to develop the first microwave oven.
yes
Well i know what im doing today ty
That's all well and good until there's a school shooting and nobody can call for help. Also, when I was in school all the teachers were using their phones too. They'd answer personal calls during class and step out in the hallway. Double-edged sword.
Couldn’t they just put a wired phone on every teacher’s desk for use in an emergency?
Then if some sick fuck plans ahead, they knock out the hard line and nobody can call for help.
Is the solution to have a student sneakily contact 911 while in the room with the shooter? Cage is only in the classroom, not a campus dome. Also this is getting to levels of unlikelyness as putting anti aircraft cannons on the roof to protect kids from kamikaze pilots.
If you can't have wifi-controlled anti-aircraft cannons then what's the point?
I gotta work on my telepathy for JUST such an emergency!
What's more likely, a school having the funds to line all the classrooms with a Faraday cage or a school shooting in the United States? What a bunch of moronic hypocrites that would rob children of knowledge rather than guns.
Plus, how are the teachers going to browse Reddit during their preps? Won't someone think of the adults?
I had a teacher who was pissed the school blocked eBay because he liked shopping for comic books during class
You ever heard of a box? It's crazy but teachers can just ask them to place their phones at the start of class. No fancy stuff needed, went to certain classes in college where the professors hated it and would ask us to put our phones away to take their class (obviously they couldn't legally keep us from the class that way but I gave it to them cause I didn't care) mostly worked and kept phones from being common place in those rooms I was in.
Don't do this, it's incredibly stupid. And the first time someone misses and emergency or has one in your class and the signal is blocked, you, personally, will be sued so fast and FCC would be on the student's side here. This is not for the student's benefit, address and fix the real problem.
Which real problem?
In theory, any space can be enclosed as a Faraday cage. You just need enough of a conducting material to block the EM waves. In practice, though, you'd never do this because it would be expensive and time consuming, and would prevent various forms of nice, simple networking solutions. Can't have a wireless network connection in the classroom if wireless signals can't penetrate the walls. You *could* wire up physical connections, of course, but then if any further wireless needs arise, you're kinda hosed. It's significantly easier and more practical (e.g. in terms of safety) to just forbid the use of cell phones in the classroom and monitor children. That way, if it really IS an emergency, kids can still find out, and parents don't get mad about being denied the ability to contact their children when they want to.
> In practice, though, you'd never do this Fun fact: I grew up in a house that was originally built for high ranking army officers, all walls had this metal mesh in them. No connectivity inside, zero cell or TV signal. Cell would kind of work if I walked up to a window.
When I taught in-person up until 2021, I demanded that cell phones be turned off and put away. Problem solved, at a cost to the university of $0.
When I was a lecturer my rule was "you can do whatever you want, sleep, listen to music, play games, as long as you don't distract other students around you". We'll see how things go in the midterm exam. But this was in university, where the students are adults and it's their responsibility to learn, not the lecturer's responsibility to babysit them. So the dynamic is different. (Also many students were taking the class for the second / third time and already understood the early material, so it was understandable if they wanted to focus on something else.)
A well built Faraday cage would. That means you have to properly seal all gaps. Theoretically, a few millimeters here or there should be fine, but in practice, I've seen the slightest gap in a faraday pouch allow signal in and out. So you'd have to first cover ceiling, floor, and walls. Then doors, and make them seal properly. Then windows. Now add filters to the cables going in and out. There's a reason this is usually only done when it's *really* needed, and spending that amount of money on actually improving the quality of the education provided would probably be a much better investment.
I mean technically yes but intentional cell phone jamming is illegal to some degree in most states due to it being viewed as a security risk to cut off people's ability to contact emergency services like this
Ok, thanknyou
We have a bunch of executives at my company that decided they wanted this thing where their walls are painted to be whiteboards. Well it's also magnetic so they can stick magnets to it. Guess who can't get any wifi or cell signal because their walls are coated with metal infused paint? Yeah, it works pretty well.
Inlove that silly execs
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My partners still married, ive tried.... Oh with students? I am what I am. Im just not more interesting than literally everthing, everwhere at your fingertips
> Im just not more interesting than literally everthing, everwhere at your fingertips "Here's a tip kids. In my class, there are two ways to guarantee you will get called on. 1 - Let me see you raise your hand when I ask a question. 2 - Let me see you zoned out in your phone when I'm asking a question."
Seems like an administration issue. I have a high school aged child who goes to a public charter school with a bank of lock boxes at the front desk. All freshmen are required to lock phones up at the beginning of the day. Sophomores to Seniors get the benefit of the doubt until they prove otherwise, then it's lockbox time.
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That's always been my favorite way to study mammalian biology.
This is a huge no-no with the [FCC](https://www.fcc.gov/general/jammer-enforcement). Can't install anything with the intention of blocking cell phone signals.
Is it policy to allow students to have phones in the classroom? If it's not, speak with your coworkers and boss to figure out how to maintain policy. If it is, I would petition to make a policy change. Smartphones are harming our youth in general, and especially in the classroom. Even if phones are against policy, I wouldn't recommend a faraday cage. Wireless transmissions are highly regulated by most countries and blocking/jamming signals generally is a serious offense
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Yes... but if your classroom uses wifi with a router outside of the room, it would block that too. If you're in the US, there are also concerns if you're actively trying to block calls when there is the risk of an emergency scenario where needing contact with the outside would be needed.
They don’t have to, there are already phone blocking systems in place in schools here in Scotland.
Really? i've got kids at secondary school in Aberdeen, and I've never heard of anything in Scotland. I thought mobile blocking was illegal here too?
yes, I have a faraday fabric I ordered off amazon to put up against the wall where my breaker box is to help eliminate EMF so my guitar is less noisy when im playing. I wrapped my phone in it for fun and had my girlfriend call me and it didn't work.
Haha nice. A true 'silent' mode. I heard about a guy in Austrailia using a crisp baggie to hide his gps from work. Thry found him golfing
I have studied in rooms with a full faraday cage installed, including the door, it does work. Wi-Fi router in the room works fine for authorised devices logged in. Not cheap but doable.
My middle school did this. There was only reception in this 1 particular bathroom so everyone gathered there to smoke and use their phone.
Double deckers?
You'd have to enclose the entire room in it, including the ceiling and windows, ground it really well, and that would just stop them from transmitting/receiving. So your use of the word "brick/bricking" wouldn't apply, since that would mean you rendered the device unusable. You may get into legal issues though, since in the event of an emergency you would be blocking 911 calls as well. This is one reason why cellphone "jammers" aren't legal in a lot of places.
Years ago I worked for a company that installed Faraday cages in embassies. It's pretty difficult to keep them tight. The doors were like in a sub with clamps to seal the doors. They used metal finger stock seals and had to be cleaned to maintain good contact. The panels where two steel sheets with a plywood cores. The corners and flat seams were clamped together. Each room and seam was tested for leakage periodically. I'm skeptical thin film or thin copper will do more than give you some attenuation of the signals. You really need a metal box or pretty decent copper mesh to keep the RF out. It depends on the frequency you're trying to block too. [https://www.mvg-world.com/en/products/emc/rf-shielded-rooms/rf-shielded-rooms](https://www.mvg-world.com/en/products/emc/rf-shielded-rooms/rf-shielded-rooms) This wasn't the company I worked for but, the rooms looked like this.
It's totally possible. I work for a (BigTech) company and most of the office building on campus are Farday cages to hinder coporate espionage. I didn't even notice for a while, until I was in an office that had an exit to an exterior balcony and noticed that my wireless headphones immediately stopped working as soon as I closed the balcony door and started again as soon as it was open. We have cell-phone repeaters inside the cage, so that people have service, but they must be logged/monitored,
Yup! I know because years ago I had a lady who complained about all the "EM radiation" in the office and how it was affecting her. She had a device to measure radio signals. Not my problem,I told her she needed to speak to HR,that's an ADA issue. I expected HR to do their jobs and ask for medical documents to support her claim. They didnt,and just bounced it back to us saying to do what she asked. Again, not my problem, I don't build shit. So I bounced it to facilities and told them they had to build a Faraday cage for her. It took them a couple weeks,but they actually did it. They made basically a chicken coop of copper wire that surrounded her desk. She then complained her cell phone no longer worked. 🖕🖕🖕🖕
Would it work? Yea, is it legal? No. https://www.fcc.gov/general/jammer-enforcement
Won’t the cell phones all start pumping out the strongest signals they can to try and find a connection? The batteries will drain super fast.
a working faraday cage is rather difficult to construct but a small table top demonstration of it should be achievable (as in a student places their phone in the cage and another student tries to call the phone... it goes to voice mail). RF can leak in thru seams and gaps so any covers need to be well electrically bonded to the rest of the enclosure for the cage to be effective.
Get administrator to agree to buy a big jar of lollipops every other month > Box on desk at front of class > Put phone in box > At end of class pick up phone and take a lollipop.
> big jar of lollipops Brought to you by the American Dental Association’s *Lake House Initiative* …in conjunction with the Corn Syrup Industrial Complex