[Johnny555]

on older phones like late 90's very early 2000's there was enough power leaking from from the antenna into the modem part that you could ping turned off phones remotely even if the battery was removed I've seen this in action

I don't see how that could work - even if power through the antenna did cause the phone to transmit something, more than the radio would have to be powered up to get the phone to return any kind of identifier. But I'm skeptical that any transmitter could be powered through the antenna like that.

I could believe that if you transmit enough power that some sort of oscillation would occur in the phone to return a signal that can be detected, but I don't see how you could determine what phone returned that signal.

[dogma1138]

It wasn't transmitting a proper cell signal, it was transmitting something that they could detect.

I would assume that you would profile phones (of a certain make and model) and based on the return signal identify them. This was used in the early days of in places where there wasn't high cellphone density to begin with.

[cmdrfred]

I wonder how that passed the FCC.

[dogma1138]

I don't think this actually violates any FCC regulations given the right circumstances a can of coke can probably be induced to create enough backscatter to be trackable via RF.