This is a super cool blog post. However I think it alludes to a much larger problem. For many products today, it’s very difficult or impossible for most people to verify the product works.
For a network switch, there are free and open source tools like iPerf to test and verify speeds are as advertised. For a faraday box, you have to go through all these steps (and knowledge learned) just to be able to test these. What about for vitamins, or pet food, or any other “durable” products that are supposed to last for X years?
In an age of snake oil salesmen, paid for reviewers, and fraudulent products on Amazon, there is a real opportunity for creating systems that enable individuals to verify products do what the sellers claim they do.
This problem was most famously studied by Akerlof in The Market For Lemons. The prediction is that such a market will be overrun with low quality lemons.
I agree that the free market is easily gamed and therefore I really am glad to be living in a country with relatively strong consumer protection laws.
I buy online, I can return within two weeks no question asked.
It breaks within two years - I return it. Either I get a repaired one or a new one or my money back.
There are few exceptions but mostly it makes shopping quite secure.
Yes. There are bad actors. Yes people get ripped off by shady online stores. But if using trusted shop, PayPal or one of the known big shopping brands the experience is mostly good.
I'd like to describe a complementary problem to yours - that it's very difficult or impossible to find out others' experiences with a product's quality, durability, and performance. That is - the complement to the problem of "it's hard to determine if some products work" is "it's hard to find other users' experiences with the product".
Amazon reviews are completely worthless, but very few other platforms have anywhere close to the same number of reviews on them. Most platforms have no verification of purchase for reviews. It's hard to determine information like "does this device require a cloud login? for which functionality? are there ads?" that isn't explicitly supplied by the manufacturer (or hidden by them). Negative reviews about product breaking quickly aren't very useful because people whose products work for a long time leave reviews at a lower rate. Google is almost useless for finding out information like this because of how SEO-gamed everything is, and the ol' "site:reddit.com" trick will only work for a while longer until these fraudsters create enough fake reviews on Reddit that it also succumbs (which is already beginning).
(rant "...and this problem will likely won't be solved anytime soon, because consumers don't care about these things. That's the reason that we're in this situation - consumer apathy. When was the last time you heard a non-tech-savvy relative say something along the lines of "Wow, this phone didn't last very long. Is there a place where I can add that data point so that other people will be more informed before they purchase one?" Users don't care about performance, privacy, or durability - they just want to watch Netflix and pay the lowest sticker price they can (regardless of annual cost of ownership). You see people self-organizing around things like video games or paintball or book clubs or whatever all the time - why won't they put even a fraction of that effort into ensuring that they buy a good car?")
> For many products today, it’s very difficult or impossible for most people to verify the product works.
Some people, when confronted with a problem, think "I know, I'll use regular expressions." Now they have two problems. - Jamie Zawinski via Coding Horror [0]
To your point, maybe Zawinski's aphorism is broader than regexp.
The quote investigation [1] linked from CH is well worth reading.
> What about for vitamins, or pet food, or any other “durable” products that are supposed to last for X years?
We could, as a society, make rules that prohibit these things and create organizations with the expertise and power to enforce those rules. We are hardly helpless, but the political trend is to forgo and even decry that power, do nothing, and then whine about how helpless we are.
tl;dw They're building a setup where they can test a bunch of computer equipment with standardised tests (built by them) in a standardised environment (also built by themselves).
I really like Snowden's recommended Faraday cage for phones or other devices of similar size: two drink-shaker cups[1].
Drink shakers are cheap and widely available. The average hotel room in any medium/large hotel chain probably includes a shaker as a standard item as part of the minibar. The simple two-cup style (as seen in [1]) is preferred over the fancier "strainer top" style because you can press the two cups together; this should cause the inner cup to slightly cut into and/or deform the outer cup along the circle where they join together. The seal between the cups should work sort of like the knife-edge seals used in vacuum chambers.
A metal box or conductive bag is only a Faraday cage if it is fully closed/sealed. Any imperfection in the seal or hole[2] might allow the radio signal to leak out. Most improvised items (freezer, random metal box, etc) have poor seals. Making a high quality cage that actually block a modern phone can be done without much trouble, but the drink shaker method is the only method I know of that will do the job using widely available (free) or very cheap ($10-ish?) parts.
If you're interested in simple cages similar in effectiveness to the EDEC Window Pouch (they drop off above 3GHz)... try a Microwave Oven. They are highly available, reasonably convenient and well designed, with pretty good quality control. You can even still see your phone inside has zero bars. I do, however, recommend unplugging the microwave (or even cutting the power cord) as a fire would likely result from cooking your hardware.
To answer [2] How big are the waves you're trying to block? - it's actually crack length not width that usually determines the effective re-radiating antenna length. They can be very narrow, but a long (a few cm) crack will allow one polarization through almost completely.
I've run this test with a GSM base station and confirmed the effectiveness. If you want to test communication with a device to a base station, but have many other local antennas interfering and want to fit many devices inside... it's a decent choice. The alternatives are less convenient and usually thousands of dollars to construct.
I think the issue is then you have to wait until you are already inside the hotel to use those shakers, which as others have said don’t actually exist in most hotels, and at that point you have been tracked to your exact location. Then it would be trivial to surveil you with other methods without needing your phone.
At one company I worked at we had an 'out of coverage bucket'. It was a zinc plated steel bucket. Worked almost every time. Some dude had found at an arts and craft store a very small version of the same thing. It fit over phones perfectly. Basically put device on ground. Put bucket over it. If you had any gaps or any cables hanging out it was sort of iffy and you would get coverage sometimes.
At my former job we had a rather large faraday cage for testing telco equipment. Two things surprised me: 1) It is more fiddly to ensure a room-sized faraday cage doesn't leak RF than I thought. It is really easy to make mistakes that compromises experiments. 2) There was a bath-towel sized piece of cloth that came with one of the expensive Rohde & Schwarz instruments that was astonishingly effective at blocking signal.
So I mainly used the room because that's where the magic blanket was - which was easier to use than ensuring the room was set up correctly.
> While the cookie tin performed much better than the mylar bags, and could provide a modicum of useful attenuation under some circumstances, it was not sufficient to provide meaningful assurance of signal isolation at any frequency. However, it was unique among the containers tested in providing tasty snacks during measurements
Back in the day working for Symbian I used to regularly have to run a load of automated Bluetooth tests. Unfortunately there were 200+ engineers in the close vicinity of my test setup and they all had smartphones and all had Bluetooth turned on, causing loads of the test to timeout. We were very pleased with ourselves when we thought of using a biscuit tin as a Faraday cage to try and improve things. Didn't work as well as we hoped, but got the tests running within their timeouts. I always thought it'd be interesting to try using an old microwave.
Best thing was that we got to eat all the biscuits first :)
Biscuit tins and aluminium foil have layers of insulation on them, the varnish of the tin and the Al2O3 oxide layer for the foil. It is true that the gap in each case is small, but when you look for 10 orders of magnitude in attenuation - a little leakage goes a long way. Silver has the unusual property in that both the metal and it's oxide are both conductors = true silver foil made of thin metallic silver will make a good wrap around Faraday bag. Even better would be true gold metal foil - note they often use gold plated shields in space uses, even though gold foil is like fly paper in space = contact welds readily, much more so than most other metals (many of which have also contact weld problems that have to be mitigated). Those Ramsey boxes are excellent, far better than many costlier, but crappier boxes, obviously made by someone who knows an ohm from a volt...
The simplest test you can make to verify that the microwave oven & biscuit tin can are good Faraday cages is to put your phone in one and try to call it - every time I did that in the past they failed to function as a Faraday cage.
When I was in jail I had a cellie who imported drugs from China. They were always shipped inside defunct microwave ovens. I wondered if it was just because it looked like a harmless kitchen appliance or because the microwave provided shielding from an x-ray scan?
The pink bag shown is actually a static dissipative bag, not a static shielding bag, so would not be expected to work. Though the article mentions trying other bags so no doubt some of those where static shielding (metallic appearance) bags.
I've had a lot of fun in the past trying to shield Bluetooth devices for testing... metal filing cabinet? Practically no attenuation. Biscuit tin? Minimal attenuation like in the article.
Modern radio receivers are ridiculously sensitive.
> "Wrap it in tin foil" is perhaps the most common advice [...] Unfortunately the results were extremely inconsistent [...] 90 dB attenuation in one test would produce only 50 dB the next time [...] You would have no way to tell whether you've managed to fold and seal it adequately well
On the other hand, aluminium foil is incredibly commonly available, if not in a kitchen draw, it will be at the nearest shop. Although unreliable, the _potentially_ high attenuation the author shared is pretty good (we don't know his worst reading), better than all other improvised solutions tested, and similar to commercial products. I wonder if a more reliable construction method could be found.
I'm not sure what movie scene scenario I'm envisioning, but in the case you needed a Faraday cage and don't constantly carry one around, perhaps simply taking an entire kitchen roll of foil and wrapping the device into a giant unsightly ball of it would be a reliable enough process for an "emergency" (if not pocket sized). i.e rather than trying to make a neatly folded minimal version, just resort to sheer number of layers of material - unless RF doesn't care and even 1000 layers with tiny gaps is no good?
[edit] Similarly, I wonder how well (or poorly) common household appliances work as a Faraday cage, e.g a fridge, microwave-oven - From what the author described, it seems they would all have too many gaps, however they are also constructed from higher gauge metals... i'm particularly interested in a microwave-oven which is specifically designed to reflect and retain microwave frequency fields.
Microwave ovens make for poor Faraday cages. The problem is that you only need 30-60dB to "keep the power in" while you probably want at least 100dB to "keep the signals out."
You can test this: put your phone in the microwave and try to call it. Over the years I have had about a 75% success rate.
Other household appliances tend to be even worse; any gaps in metallic seals effectively turn into slot antennas and let signals through. You need a conductive mesh gasket to stop this, and I generally don't see mesh gaskets on consumer appliances.
Your "make an al-foil ball" strategy is what I would resort to in a pinch (I have some nice Anritsu shield boxes, but those are cheating). Quantity is a quality of its own. My only addition would be making sure that the gaps tend to not line up. You want to make it difficult for the "slot antennas" modeling the gaps in each layer to couple to each other.
Microwave-ovens definitely don't leak below 2.4 GHz. Any frequency above that is a non-issue for microwave-oven operator safety. It also wouldn't be an issue for any communication device transmitting below 2.4 GHz. If you want to shut down 5 GHz communication then a microwave-oven would be leaky. 60 GHz: it shouldn't matter since it needs LoS anyway.
I wish it covered (so to speak) aluminum foil more thoroughly.
In particular, foil is cheap, so rolling up in several layers (3? 5? 10?) and twisting the ends cracker-style ought to be more reliable and practical than trying to do it with one layer and fiddly seams. A suggested minimum number of layers and number of twists would be useful.
I wish it had covered practical tests more thoroughly. As in: did the phone communication effectively drop dead once in the cages which measure well? Looks very likely based on those attenuation numbers, but still: 'question everything' is usually the way to go in test&measurement.
I built something in college that needed UL testing for RF emissions, and visited a facility in Long Island with a TEMPEST room about the size of my house. Was very memorable.
I also read an article this year by a guy that made his house radio-wave proof, because, he claimed, he was very sensitive to radio waves. It was WAY more involved than I would have guessed - for the same reasons discussed in this article and in this HN discussion. Nails and screws are a problem. Windows are a big problem. But still - how cool to be cut off from the onslaught of EM radiation.
Cheap science fiction book idea: imagine having to choose between living without your smartphone or living with every company and government agency willy-nilly spying on you. Oh, wait...
Please reduce the image size, they seem to be 3 Mb each.
Some people (especially if their phone is in a pouch) won't be able to get to the interesting parts of your article!
The metal tin box will have had varnish and paint on it's surfaces.
That means at the junction between the tin and the lid (and maybe other joins), there isn't an electrical connection all along.
Having two metal surfaces next to eachother, but with an insulator in between, acts like a 'choke flange'[1]. However, they only work at one specific frequency - at all other frequencies they will leak either a little signal or a lot/all the signal.
The same technique is used on a microwave door edge to keep the microwaves in. It's why keeping the microwave door edge clean is critical to safety - a small bit of food there isn't an insulator like the paint, and energy leaks out.
Interesting results. The article states that Faraday cages are no directional. My physics 101 understanding of them was otherwise. You show they work by integrating over the surface of the cage and saying that's equal to the charge within the surface. But you don't say it's equal to the charge outside. Indeed it couldn't possible, since that charge could be light-years away and steady state would never be achieved. Now that was for electrostatic which isn't really what we care about, if I remember correctly.
Wikipedia also states they are more effective at blocking incoming than outgoing signals. Can anyone clarify the situation?
Building an effective Faraday Screen is surprisingly difficult:
There are three completely different scenarios, blocking electrostatic fields, blocking RF energy, and blocking alternating magnetic fields.
The first can be achieved by a thin conductive screen (eg brass mesh with soldered seams), the second by thick copper sheet (with bolted seams) and the third requires thick magnetic material (eg iron or nu-metal).
If you consider the compactification of R^3 by a single point “at infinity”, an electric charge inside the surface is the same as the opposite charge at infinity (this is just Gauss’ result). In that sense, “infinity” acts as the opposite charge, does it not?
I do not understand your question, otherwise.
(Not a criticism, just an interested comment which may be very wrong though).
That red plastic "mylar bag" isn't what should have been tested.
Red plastic == electrostatic dissipative. It is not good at conducting electricity -- it is still very good insulator. It just has ability to dissipate electric charge fast enough so that it will not accumulate in normal use.
What you have wanted to check is a clear bag with metalized layer (which is silver or gray looking). It should, per my understanding, act as much better faraday cage than an electrostatic dissipative bag. And I would be really interested in seeing that measurement.
This article was a fun read, and it really highlights how we trust the words on the tin to be accurate and not mistaken marketing gibberish.
However, the part about the cost ranging from $40 - $80 is simply not true. I know this, because I purchased for $20 yesterday a faraday box to hold my auto key fobs and my cell phone. [1] There are very many items for sale at this price point, fabric, pouches and boxes.
Even if the radio is blocked, how does that stop a device from collecting data anyway, and exfiltrating it the moment it finds a network? Won't it look for a network the moment you take it out of the bag? And don't you have to remove it from the bag to use it practically?
Ultimately, if your device is compromised or untrustworthy to the extent that it has to be policed this way, is it not safer to just... get rid of it?
I still wonder why phone cases with physical blockers for camera and mic aren’t in high demand, and why there aren’t hundreds of pirated copies on the market for the ones that have been developed.
I think they could have done a better job with the aluminum foil. It looks rather not well done. He could have made a pouch and folded the sides over a few times.
I made a pouch for my car's key fob with aluminum foil and metal tape. It isn't as pretty as the ones you can buy, but it wasn't $25 either and It has worked really well.
Glad to see these tested. I've been using the EDEC bags for probably a decade to have on hand for incident response/forensics in security consulting, but I never had the gear to test the bags, I just trusted their supplier. Good to know about millimeter wave / 5g though.
One thing that most people should use a Faraday pouch for (in my opinion) is storing your key fobs if your vehicle uses keyless ignition with a fob. This prevents a very common relay attack which is to stand with a laptop by someone's front door and relay the keyfob signal between the keys (somewhere inside the person's house) and the car. For people who live in cities where you park on the street (as I do) it's extra-convenient for thieves in that most cars will flash some lights to say the alarm is disabled so the thieves know which car they just unlocked.
I'd be curious if anyone finds it worthwhile to have a smartphone while being so paranoid that you have to hide it in a Faraday bag. I understand the problem. I just don't understand the practical use case: every time you use the phone, you have to take it out of the Faraday bag, and it can be used to spy on you or report information about you. Assuming you're keeping it in the Faraday bag all day, when and why would you find it useful and worth the risk to take it out? And with that level of use, wouldn't it be more practical to have a dumb phone or a laptop?
You would take out your phone if you would like to make a phone call, or check to see if you have received any messages. For the other 99% of your day, the IoT sensors being stuck on every conceivable object are unable to report back to HQ (and every agency and broker affiliated) your current whereabouts and trajectory.
Interesting experiment however his experience with tinfoil and metal boxes doesn't match mine.
I placed my phone wrapped in a towel inside a metal box: as soon as I close the lid I can't ping the phone on local WiFi and can't reach it with call (it goes direct to voicemail as if the phone was switched off). The GPS doesn't record any position while in the box.
I didn't test the Bluetooth though.
Same thing for my car keys inside a paper towel and aluminum foil: impossible to open the car even at touching distance.
I wonder if he wrapped the device before putting it in the box or aluminum.
I visited at the end of eighties a research institute in a former USSR. They had a whole room with computers put in a Faraday cage to prevent any data leaks with supposedly secret information. The cage was a mesh made of thin metal sheets with 1mm holes. As I remember the whole thing was done seriously, not a fake to please some inspector. It had double doors, all cables were put into metal tubes, all lights were outside I suppose to minimize the cabling.
Electronic voting machines should be put inside Faraday cages too. Specially now that communication chips have been found hidden in some of their motherboards.
Btw, to prevent abovementioned government/other powerful groups intrusions into our minds, I recommend to stop consuming MSM. That's the most powerful tool of intrusion/control they have.
I've lately started seeing claims on some of the forums that embrace things like vaccines contain 5G mind control chips claiming that lead effectively blocks government mind control and that is the real reason lead paint was banned, and that it is not actually harmful.
Per-se, yes, agreed, but I was wondering whether the transmitter and receiver antenna couple into the surrounding screen differently. The degree of coupling may de-tune them differently. If so then the setup which most accurately represents the intended use would be with the receiver inside the screen.
Idle comment: we use their smaller keychain bags for car fobs, after hearing with dismay first- and second- hand accounts of relay attacks being used to steal or ransack cars in our neighborhood (94110). We now keep our fobs in them except in use.
What is the use case for disabling wireless communication for your phone? How will you use it? How will anyone call you? If you don't want to use wireless functions, buy a tablet that lacks all the radio hardware.
Bad Guys can't follow you using the signal. That's about it. Sure, they can tail you, but that's Work. And they'll know where you are the moment you take it out, but hopefully they're too far away to act on it.
All in all, if you NEED something like this, your opec had better include more than this.
TIL: Two principal types of scaling of the decibel are in common use. When expressing a power ratio, it is defined as ten times the logarithm in base 10. That is, a change in power by a factor of 10 corresponds to a 10 dB change in level. When expressing root-power quantities, a change in amplitude by a factor of 10 corresponds to a 20 dB change in level. The decibel scales differ by a factor of two, so that the related power and root-power levels change by the same value in linear systems, where power is proportional to the square of amplitude.
Tinfoil hat on - has anyone considered how suspicious that only the commercial products worked, maybe the post is just a very clever shill for those products?
> Tinfoil hat on - has anyone considered how suspicious that only the commercial products worked, maybe the post is just a very clever shill for those products?
Not really, tinfoil actually worked, but it was apparently too difficult to get right:
> In my experiments, I found I could sometimes achieve approximately 90 dB attenuation by carefully wrapping the generator in foil and double folding the seams on all sides, which is quite good (comparable to commercial pouches).
This actually matches my experience with a GPS logger. It only had an on/off switch and I wanted to download the track from my trip without getting points from the download location at the end. IIRC, it was still able to get fixes even wrapped in tin foil.
My understanding is that a Faraday Cage, of any size, relies on a proper grounding system to work at all so these boxes and rfid blocking pockets etc all seem to be tinfoil hats parading as space age metamaterials.
A faraday cage converts the energy in the radio waves it absorbs into heat.
Eventually it will radiate the same amount of energy as the transmitter inside it, but in infrared wavelengths and without whatever modulation was carrying the signal.
SamuelAdams|4 years ago
For a network switch, there are free and open source tools like iPerf to test and verify speeds are as advertised. For a faraday box, you have to go through all these steps (and knowledge learned) just to be able to test these. What about for vitamins, or pet food, or any other “durable” products that are supposed to last for X years?
In an age of snake oil salesmen, paid for reviewers, and fraudulent products on Amazon, there is a real opportunity for creating systems that enable individuals to verify products do what the sellers claim they do.
readams|4 years ago
https://en.wikipedia.org/wiki/The_Market_for_Lemons
sdoering|4 years ago
I buy online, I can return within two weeks no question asked.
It breaks within two years - I return it. Either I get a repaired one or a new one or my money back.
There are few exceptions but mostly it makes shopping quite secure.
Yes. There are bad actors. Yes people get ripped off by shady online stores. But if using trusted shop, PayPal or one of the known big shopping brands the experience is mostly good.
throw10920|4 years ago
Amazon reviews are completely worthless, but very few other platforms have anywhere close to the same number of reviews on them. Most platforms have no verification of purchase for reviews. It's hard to determine information like "does this device require a cloud login? for which functionality? are there ads?" that isn't explicitly supplied by the manufacturer (or hidden by them). Negative reviews about product breaking quickly aren't very useful because people whose products work for a long time leave reviews at a lower rate. Google is almost useless for finding out information like this because of how SEO-gamed everything is, and the ol' "site:reddit.com" trick will only work for a while longer until these fraudsters create enough fake reviews on Reddit that it also succumbs (which is already beginning).
(rant "...and this problem will likely won't be solved anytime soon, because consumers don't care about these things. That's the reason that we're in this situation - consumer apathy. When was the last time you heard a non-tech-savvy relative say something along the lines of "Wow, this phone didn't last very long. Is there a place where I can add that data point so that other people will be more informed before they purchase one?" Users don't care about performance, privacy, or durability - they just want to watch Netflix and pay the lowest sticker price they can (regardless of annual cost of ownership). You see people self-organizing around things like video games or paintball or book clubs or whatever all the time - why won't they put even a fraction of that effort into ensuring that they buy a good car?")
adolph|4 years ago
Some people, when confronted with a problem, think "I know, I'll use regular expressions." Now they have two problems. - Jamie Zawinski via Coding Horror [0]
To your point, maybe Zawinski's aphorism is broader than regexp.
The quote investigation [1] linked from CH is well worth reading.
0. https://blog.codinghorror.com/regular-expressions-now-you-ha...
1. http://regex.info/blog/2006-09-15/247
wolverine876|4 years ago
We could, as a society, make rules that prohibit these things and create organizations with the expertise and power to enforce those rules. We are hardly helpless, but the political trend is to forgo and even decry that power, do nothing, and then whine about how helpless we are.
dannyw|4 years ago
mfkp|4 years ago
https://www.consumerlab.com/ does a great job testing vitamins and other various things put in or on your body. Well worth the subscription price.
theshrike79|4 years ago
tl;dw They're building a setup where they can test a bunch of computer equipment with standardised tests (built by them) in a standardised environment (also built by themselves).
RandallBrown|4 years ago
The post does mention something similar near the bottom where they suggest putting an AirTag in the bag and seeing if your phone can find it.
pdkl95|4 years ago
Drink shakers are cheap and widely available. The average hotel room in any medium/large hotel chain probably includes a shaker as a standard item as part of the minibar. The simple two-cup style (as seen in [1]) is preferred over the fancier "strainer top" style because you can press the two cups together; this should cause the inner cup to slightly cut into and/or deform the outer cup along the circle where they join together. The seal between the cups should work sort of like the knife-edge seals used in vacuum chambers.
A metal box or conductive bag is only a Faraday cage if it is fully closed/sealed. Any imperfection in the seal or hole[2] might allow the radio signal to leak out. Most improvised items (freezer, random metal box, etc) have poor seals. Making a high quality cage that actually block a modern phone can be done without much trouble, but the drink shaker method is the only method I know of that will do the job using widely available (free) or very cheap ($10-ish?) parts.
[1] https://ae01.alicdn.com/kf/HLB1yRyhXZTxK1Rjy0Fgq6yovpXaZ/Win...
[2] Holes of sufficient size. How big are the waves you are trying to block?
adolph|4 years ago
Maybe the hotels you stay in, Bond, James Bond.
GordonS|4 years ago
I've stayed in dozens of hotels all over the world, and never once have I seen a cocktail shaker in the minibar?!
ncmncm|4 years ago
And I don't recall ever finding one of these things in a hotel room, even in Europe.
MR4D|4 years ago
“Security Mints - sweet & secure”.
Maybe a kickstarter?
kurthr|4 years ago
To answer [2] How big are the waves you're trying to block? - it's actually crack length not width that usually determines the effective re-radiating antenna length. They can be very narrow, but a long (a few cm) crack will allow one polarization through almost completely.
I've run this test with a GSM base station and confirmed the effectiveness. If you want to test communication with a device to a base station, but have many other local antennas interfering and want to fit many devices inside... it's a decent choice. The alternatives are less convenient and usually thousands of dollars to construct.
causi|4 years ago
14|4 years ago
sumtechguy|4 years ago
bborud|4 years ago
So I mainly used the room because that's where the magic blanket was - which was easier to use than ensuring the room was set up correctly.
op00to|4 years ago
scottdupoy|4 years ago
Back in the day working for Symbian I used to regularly have to run a load of automated Bluetooth tests. Unfortunately there were 200+ engineers in the close vicinity of my test setup and they all had smartphones and all had Bluetooth turned on, causing loads of the test to timeout. We were very pleased with ourselves when we thought of using a biscuit tin as a Faraday cage to try and improve things. Didn't work as well as we hoped, but got the tests running within their timeouts. I always thought it'd be interesting to try using an old microwave.
Best thing was that we got to eat all the biscuits first :)
aurizon|4 years ago
redleader55|4 years ago
Edit: clarification.
kingcharles|4 years ago
Terry_Roll|4 years ago
parkertomatoes|4 years ago
After searching, I found that Kaspersky has a blog post on the topic: https://usa.kaspersky.com/blog/terminator-dark-fate-chips/18...
It surprised me that chip bags were more effective in their test than cookie tins, but only when they double-bagged it
teddyh|4 years ago
alliao|4 years ago
https://arstechnica.com/information-technology/2017/11/austr...
janekm|4 years ago
I've had a lot of fun in the past trying to shield Bluetooth devices for testing... metal filing cabinet? Practically no attenuation. Biscuit tin? Minimal attenuation like in the article.
Modern radio receivers are ridiculously sensitive.
deelowe|4 years ago
> "Makeshift Pouch 1: Electrostatic Mylar Bag"
This is not a mylar bag. It's frustrating how often these two are confused, especially when said confusion can result in component damage.
tomxor|4 years ago
On the other hand, aluminium foil is incredibly commonly available, if not in a kitchen draw, it will be at the nearest shop. Although unreliable, the _potentially_ high attenuation the author shared is pretty good (we don't know his worst reading), better than all other improvised solutions tested, and similar to commercial products. I wonder if a more reliable construction method could be found.
I'm not sure what movie scene scenario I'm envisioning, but in the case you needed a Faraday cage and don't constantly carry one around, perhaps simply taking an entire kitchen roll of foil and wrapping the device into a giant unsightly ball of it would be a reliable enough process for an "emergency" (if not pocket sized). i.e rather than trying to make a neatly folded minimal version, just resort to sheer number of layers of material - unless RF doesn't care and even 1000 layers with tiny gaps is no good?
[edit] Similarly, I wonder how well (or poorly) common household appliances work as a Faraday cage, e.g a fridge, microwave-oven - From what the author described, it seems they would all have too many gaps, however they are also constructed from higher gauge metals... i'm particularly interested in a microwave-oven which is specifically designed to reflect and retain microwave frequency fields.
jjoonathan|4 years ago
You can test this: put your phone in the microwave and try to call it. Over the years I have had about a 75% success rate.
Other household appliances tend to be even worse; any gaps in metallic seals effectively turn into slot antennas and let signals through. You need a conductive mesh gasket to stop this, and I generally don't see mesh gaskets on consumer appliances.
Your "make an al-foil ball" strategy is what I would resort to in a pinch (I have some nice Anritsu shield boxes, but those are cheating). Quantity is a quality of its own. My only addition would be making sure that the gaps tend to not line up. You want to make it difficult for the "slot antennas" modeling the gaps in each layer to couple to each other.
willis936|4 years ago
Also, remember to ground your faraday cages.
tomkat0789|4 years ago
ncmncm|4 years ago
In particular, foil is cheap, so rolling up in several layers (3? 5? 10?) and twisting the ends cracker-style ought to be more reliable and practical than trying to do it with one layer and fiddly seams. A suggested minimum number of layers and number of twists would be useful.
rasz|4 years ago
stinos|4 years ago
intrasight|4 years ago
I also read an article this year by a guy that made his house radio-wave proof, because, he claimed, he was very sensitive to radio waves. It was WAY more involved than I would have guessed - for the same reasons discussed in this article and in this HN discussion. Nails and screws are a problem. Windows are a big problem. But still - how cool to be cut off from the onslaught of EM radiation.
lettergram|4 years ago
Perhaps it sounds like overkill, but it’s the only way I seem to be able to fully isolate the devices.
That said, I’d probably just buy a bag... but I’ve been trying to keep it with what I have lying around the house.
dsign|4 years ago
jpl56|4 years ago
JohnJamesRambo|4 years ago
londons_explore|4 years ago
That means at the junction between the tin and the lid (and maybe other joins), there isn't an electrical connection all along.
Having two metal surfaces next to eachother, but with an insulator in between, acts like a 'choke flange'[1]. However, they only work at one specific frequency - at all other frequencies they will leak either a little signal or a lot/all the signal.
The same technique is used on a microwave door edge to keep the microwaves in. It's why keeping the microwave door edge clean is critical to safety - a small bit of food there isn't an insulator like the paint, and energy leaks out.
[1]: https://en.wikipedia.org/wiki/Waveguide_flange#Choke_connect...
f38zf5vdt|4 years ago
0xdeadb00f|4 years ago
noduerme|4 years ago
shapefrog|4 years ago
I do miss the old days of tuning the rabbit ears on top of the tv for best reception.
tgb|4 years ago
Wikipedia also states they are more effective at blocking incoming than outgoing signals. Can anyone clarify the situation?
Johnythree|4 years ago
There are three completely different scenarios, blocking electrostatic fields, blocking RF energy, and blocking alternating magnetic fields.
The first can be achieved by a thin conductive screen (eg brass mesh with soldered seams), the second by thick copper sheet (with bolted seams) and the third requires thick magnetic material (eg iron or nu-metal).
pfortuny|4 years ago
I do not understand your question, otherwise.
(Not a criticism, just an interested comment which may be very wrong though).
djmips|4 years ago
catlikesshrimp|4 years ago
https://www.androidpolice.com/2020/08/22/this-smartphone-has...
Or at least phone with a removable battery
I know I will never buy a phone without a 3.5 audio jack
jmnicolas|4 years ago
Depending on your occupation it can have very serious consequences.
pdkl95|4 years ago
marginalia_nu|4 years ago
bserge|4 years ago
[deleted]
lmilcin|4 years ago
Red plastic == electrostatic dissipative. It is not good at conducting electricity -- it is still very good insulator. It just has ability to dissipate electric charge fast enough so that it will not accumulate in normal use.
What you have wanted to check is a clear bag with metalized layer (which is silver or gray looking). It should, per my understanding, act as much better faraday cage than an electrostatic dissipative bag. And I would be really interested in seeing that measurement.
IncRnd|4 years ago
However, the part about the cost ranging from $40 - $80 is simply not true. I know this, because I purchased for $20 yesterday a faraday box to hold my auto key fobs and my cell phone. [1] There are very many items for sale at this price point, fabric, pouches and boxes.
[1] https://smile.amazon.com/s?k=faraday+box
pro_zac|4 years ago
Tronno|4 years ago
Even if the radio is blocked, how does that stop a device from collecting data anyway, and exfiltrating it the moment it finds a network? Won't it look for a network the moment you take it out of the bag? And don't you have to remove it from the bag to use it practically?
Ultimately, if your device is compromised or untrustworthy to the extent that it has to be policed this way, is it not safer to just... get rid of it?
sanirank|4 years ago
comeonseriously|4 years ago
I made a pouch for my car's key fob with aluminum foil and metal tape. It isn't as pretty as the ones you can buy, but it wasn't $25 either and It has worked really well.
motohagiography|4 years ago
seanhunter|4 years ago
skunkworker|4 years ago
https://www.reddit.com/r/whatisthisthing/comments/r7kb03/my_...
yosito|4 years ago
24bug47|4 years ago
jmnicolas|4 years ago
I placed my phone wrapped in a towel inside a metal box: as soon as I close the lid I can't ping the phone on local WiFi and can't reach it with call (it goes direct to voicemail as if the phone was switched off). The GPS doesn't record any position while in the box. I didn't test the Bluetooth though.
Same thing for my car keys inside a paper towel and aluminum foil: impossible to open the car even at touching distance.
I wonder if he wrapped the device before putting it in the box or aluminum.
mnw21cam|4 years ago
_0w8t|4 years ago
gdelfino01|4 years ago
https://letsfixstuff.org/2021/04/modem-chips-embedded-in-vot...
effie|4 years ago
pseudolus|4 years ago
http://web.archive.org/web/20100708230258/http://people.csai...
effie|4 years ago
tzs|4 years ago
bflesch|4 years ago
But how come these are all US-exclusive. It seems both winners don't ship to EU :/
whiw|4 years ago
Per-se, yes, agreed, but I was wondering whether the transmitter and receiver antenna couple into the surrounding screen differently. The degree of coupling may de-tune them differently. If so then the setup which most accurately represents the intended use would be with the receiver inside the screen.
aaroninsf|4 years ago
Idle comment: we use their smaller keychain bags for car fobs, after hearing with dismay first- and second- hand accounts of relay attacks being used to steal or ransack cars in our neighborhood (94110). We now keep our fobs in them except in use.
wolverine876|4 years ago
jagged-chisel|4 years ago
All in all, if you NEED something like this, your opec had better include more than this.
BongoMcCat|4 years ago
I always thought it was 10dB, or one B that was a change of factor 10. Have I missed something?
variaga|4 years ago
Power is proportional to voltage squared.
So a 10x increase in voltage == a 10^2 = 100x increase in power == a 20dB increase in power.
js2|4 years ago
https://en.wikipedia.org/wiki/Decibel
WalterBright|4 years ago
I tested some by putting the phone in the Faraday container, and then calling its number to see if it rang.
fsflover|4 years ago
323|4 years ago
docflabby|4 years ago
tablespoon|4 years ago
Not really, tinfoil actually worked, but it was apparently too difficult to get right:
> In my experiments, I found I could sometimes achieve approximately 90 dB attenuation by carefully wrapping the generator in foil and double folding the seams on all sides, which is quite good (comparable to commercial pouches).
This actually matches my experience with a GPS logger. It only had an on/off switch and I wanted to download the track from my trip without getting points from the download location at the end. IIRC, it was still able to get fixes even wrapped in tin foil.
unknown|4 years ago
[deleted]
unknown|4 years ago
[deleted]
ziggus|4 years ago
pluc|4 years ago
zanybear|4 years ago
Ntrails|4 years ago
Wistar|4 years ago
jimmySixDOF|4 years ago
snowwrestler|4 years ago
Eventually it will radiate the same amount of energy as the transmitter inside it, but in infrared wavelengths and without whatever modulation was carrying the signal.
formerly_proven|4 years ago
does not
authed|4 years ago
dtgriscom|4 years ago
h2odragon|4 years ago
0xdeadb00f|4 years ago
I've made a few DIY Faraday bags that way. They're not perfect of course, but less expensive than these bags most of the time.
Edit: Ah, I see this was covered in the article. I didn't read it before posting this comment.
taneq|4 years ago