[dogma1138]

It's very old phones, with external antennas the power came from the same place that the power came from to say power the LED in the aftermarket NOKIA antennas that would light up when you are getting a call or a text - wireless power. The phone had enough leakage to modulate the return signal sufficiently to be detected, it would not be the same thing as tracking a phone via its normal cellular signal it would just indicate the presence of one.

[quesera]

I don't believe this.

Those aftermarket lighty-uppy things work by sensing your phone's response burst, which is a much stronger signal, being driven by the phone's battery, and radiated from the very nearby antenna.

I do believe that you can induce a signal in a powered-off phone that can be detected nearby (several feet), by virtue of the tuned antenna if nothing else. I'm skeptical of the claim that a normal arbitrarily-distant cell transmission could do so. Regardless, I do not believe the induced signal could be detected back at the cell tower.

This would be wireless power. Not possible, at the levels and ranges asserted.

[dogma1138]

Believe what you want but at least read it through first. This isn't about powering a cell phone via wireless power and make it connect to a cell tower this is about inducing enough power into the cell phone's RF parts to make it modulate the signal sufficiently to be able to be picked up. Essentially this isn't that much different than the passive wifi or any other backscatter communication based system.

I've seen this demonstrated around 5 years ago at an Intelligence Technology seminar open to the public at the intelligence community heritage museum, it was done across the room during a demonstration which showed active and passive phone tracking techniques (they put the phones in and out of a faraday cages during the demonstration). The phone that was used in the demonstration for the "powerless" tracking was a very old Ericsson (before it became Sony Ericsson) phone from the mid to late 90's, during that demonstration we've also been told that this method of tracking became obsolete around the early 2000's. They did not elaborate exactly what ranges this work on but what they said is that the emitter and receiver were usually separated in order to accommodate operational requirements.

[quesera]

As I read it, that's a fine way to detect the presence of a cell phone. It might be able to discriminate between several models of cell phones. But it will not be able to identify a specific cell phone.

Am I misreading your statements?

[dogma1138]

Yes, I said it was used to track cell phones in low density areas back when they were simply enough for this trick to work, what I assume is that if someone back then had a cell phone/radio phone/sat phone or anything similar with a susceptible transmitter in the middle of nowhere-stan you could probably identify them via other means, or at least be able to classify them sufficiently.

[quesera]

That makes sense. I think I veered off into confusion from the comment about the inductively-powered LEDs.