Testing Faraday Cages
Matt Blaze tested a variety of Faraday cages for phones, both commercial and homemade.
The bottom line:
A quick and likely reliable “go/no go test” can be done with an Apple AirTag and an iPhone: drop the AirTag in the bag under test, and see if the phone can locate it and activate its alarm (beware of caching in the FindMy app when doing this).
This test won’t tell you the exact attenuation level, of course, but it will tell you if the attenuation is sufficient for most practical purposes. It can also detect whether an otherwise good bag has been damaged and compromised.
At least in the frequency ranges I tested, two commercial Faraday pouches (the EDEC OffGrid and Mission Darkness Window pouches) yielded excellent performance sufficient to provide assurance of signal isolation under most real-world circumstances. None of the makeshift solutions consistently did nearly as well, although aluminum foil can, under ideal circumstances (that are difficult to replicate) sometimes provide comparable levels of attenuation.
Winter • December 3, 2021 6:50 AM
“although aluminum foil can, under ideal circumstances (that are difficult to replicate) sometimes provide comparable levels of attenuation.”
This is undoubtedly true, but aluminum foil is easily obtained, can protect objects as large as you want, can be double folded to any desired thickness, and can be folded “air tight” if you make an effort. If you want it grounded, that is not that difficult to achieve (if you have a good ground, that is).
Yes, a $1000 special purpose Faraday Pouch is much better. But if that is not handy, go for aluminum foil.