For Liars and Loafers, Cellphones Offer an Alibi

[Major Variola (ret)]

At 06:38 AM 6/27/04 +0200, Thomas Shaddack wrote:
>If the phone is shielded, it can't transmit/receive, which makes it
rather
>useless. :(

When you don't want to use it, why should it not be useless?

>There is one potential landmine as well; the inherent ability of any
>device containing resonators to behave like a crude RFID tag. I heard
>somewhere, and my memory may be failing, that it is possible to
irradiate
>the phone with the frequency of the cellular band, and it faintly
>resonates and returns back its own echo, which has minute variations
given
>by type, manufacturing tolerances, and possibly age of the phone,
giving
>it a kind of unique signature. (This could potentially apply also to
>radios and transceivers. Does anybody have any idea if it is possible
to
>do such kind of "active fingerprinting" of rf devices? This way it
should
>be possible to detect even powered-off devices like hidden transceivers
or
>body wires; take a transmitter, sweep the spectrum, and watch echoes on

>the receiver - there could be peaks on the frequencies of the tuned
>circuits inside the examined device.)

Your "second order effect" physics is on target.  Nonlinear devices
generate harmonics when tickled.  All devices vary and have
characteristic
RF signatures.  I read something about that recently somewhere, but
memory fails.

>Question to RF heads here: could it work?

I'm not an Elmer but I pretend to be one on the internet.