On Mon, 09 Oct 2006 22:23:22 +0100, Joey
wrote:

Suppose someone visited your office or home and tried to make a voice
recording using a hidden recorder.


Ok, why do you care?
Don't have sensitive conversations with anyone you can't
trust, if you're going to be saying anything that shouldn't
be recorded.


If they used a older-style dictation machine based on tape then you
could detect the electromagnetic transmissions from the dictation
machine when it was recording.

Doubtful, and not worth the bother when you could just scan
them or search them physically.



But how would you detect if someone was secretly recording with an MP3
player that recorded to flash memory?

Scan them or search them.
What makes you think you should detect it?
Don't they have a right to a recording of any conversation
they're participating in?


Is there some transmission which could be detected?

Do you mean "wild hypothetical way that some future
technology or extremely expensive equipment and controlled
environment could detect", or do you mean, practically
speaking?


Perhaps some low power ultra high frequency from chip refresh cycles?

.... and you're discriminate this from everything else, all
other HF noise, how? Get a baseline maybe, but noise is
random unless a controlled environment.

You just need to have everyone strip down nude and then do
body cavity searches, X-Rays, exploratory surgery, then
never let them leave so it doesn't really matter if anything
was recorded so long as the environment has sufficient RF
shielding.