i imagine it might be possible to detect the resonance of the antenna or somthing, dunno
Yeah metal detectors exists long time ago, even these detectors can detect the main 3 metals used in the industry but a turned off phone how the hell transmits data? Otherwise how else way you identify the phone?
Outside of a controlled environment - like the aforementioned lab, cell phones can not be remotely tracked or traced if turned off. Period.
There might be an RFID tag inside the handset equipment (phone), for the purpose of inventory tracking at the manufacturer. Though to get higher distances (like over a meter) one has to get quite directional with the scanning.
Chemist, can you describe the equipment used for detecting the powered down phones? Also, was it able to identify the phone, or just know there was a phone somewhere? The latter could even be an antenna resonance trick of some kind, but I doubt it would be possible to identify/discern two different phones of same model with that.
Edit:
On the original topic, for the ~20 years cellphones have been available to average consumers, there has been rumors that the government/teleoperator/CIA/Mafia has ability to activate a cellphone remotely for tracking or eavesdropping purposes even when seemingly powered off, the GPS location seems like a natural continuity for that. My honest guess is that it is not possible on the stock equipment out from the manufacturer. However, as with all IT security, if the hostile party can get physical access to your device, at any point of time, you're screwed. One way or other.
I have no reason to be too worried about this stuff. If someone truly has, my advice is: Simply, and completely, stay away from (a) technology, (b) other people.
1) GPS chip don't transmit anything (but your phone still might)
2) Do you think any government would let other countries have control on the cell phones of their own citizens? Very remotely imaginable for not-imported USA-specific phones (that would be customly modified for the USA market). Never going to happen in most of the world (hey, at least europe/asia).
I feel sure that since 2003 or 4 when this took place, Govt has probably required this backdoor in most cell phones sold in US...or required carriers to have ability
In the light of this, i wonder how profitable it would be to sell modified mobiles with a physical switch to mute the microfone and cut the power to the camera...
Just side note - modern (aka produced in last 10 years ;P ) cell phones *do* receive special signals from cell towers even when turned off, after logout signal. They (turned off phones) normally *don't* send any signals - but, filtering conspiracy theories for some meritocratic content, there *is* possibility to include "act-dead wakeup", upon getting special, secret kind of signal from cell tower.
Still, AFAK most phones stop actively receiving any signals when battery is pulled out. Still, in modern technology era, and considering how low-level and low-bandwidth those signals can be, i would not be surprised, if some chip on phone would contain special backup power *just* for receiving this kind of signals.
Ho ever, I think it's not possible yet, to create such small and "sneaky" power source, than can power-up phone systems so much to *send* answer for that signal. Of course we're still talking about battery pulled-out scenario.
