I'm going to go ahead and assert that they can't tell. A Faraday cage is just a deliberate construction of a situation that happens all the time anyway. Hospitals have lots of shielded rooms in and around the radiology department. The basement of a steel building is basically the same. So is anywhere on a ship. My aged house has lath and plaster walls that can simultaneously survive a nuclear blast and also block Wi-Fi unless the amp's turned up to 11. There's no sensor in an iPhone that could tell that it's in a specially-constructed Faraday cage instead of a plain old dresser drawer in my bedroom.
I'm not sure if that's possible. What's the difference between that and someone sitting their phone on a metal cabinet?
I'm even more confident that Apple hasn't spent the research hours required to do that reliably, then incorporate the electronics and software needed into off-the-shelf phones, all to protect criminals from having their phones hacked under very specific conditions. That seems like a huge money sink.
> What's the difference between that and someone sitting their phone on a metal cabinet?
In a zero-signal environment? With other iPhones in very close proximity?
You can even measure your false positive rate by timing to first successful unlock. If it happens more than once, turn down the sensitivity on the feature (or turn it off completely).
(Were I designing this feature, I’d let phones in this state poll the other phones on how long they’ve been in it.)
