Well shielded (for example, wrapped to copper foil), 1.5V AAA powered device
will give EMI below ambient level. If its clock generator employs spread
spectrum, it's even more difficult to detect.

"Joey" wrote in message
...
Suppose someone visited your office or home and tried to make a voice
recording using a hidden recorder.

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.

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

Is there some transmission which could be detected?
Perhaps some low power ultra high frequency from chip refresh cycles?

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

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.

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

Is there some transmission which could be detected?
Perhaps some low power ultra high frequency from chip refresh cycles?
WEll, you could just stick an antenna up next to the player
and see.
This is what a sandisk looks like playing mp3s.
Can you tell which trace is of the sandisk?
Reading the title is cheating...
http://nm7u.tripod.com/homepage/nothin.jpg
http://nm7u.tripod.com/homepage/sandisk.jpg
mike

Can you also wrap sandisk in copper foil and do the same exercise?

"mike" wrote in message
newsdAZg.3099$3C6.2932@trnddc04...
Joey wrote:
Suppose someone visited your office or home and tried to make a voice
recording using a hidden recorder.

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.

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

Is there some transmission which could be detected? Perhaps some low
power ultra high frequency from chip refresh cycles?
WEll, you could just stick an antenna up next to the player
and see.
This is what a sandisk looks like playing mp3s.
Can you tell which trace is of the sandisk?
Reading the title is cheating...
http://nm7u.tripod.com/homepage/nothin.jpg
http://nm7u.tripod.com/homepage/sandisk.jpg
mike

Alexander Grigoriev wrote:
Can you also wrap sandisk in copper foil and do the same exercise?

If you can't the see anything without the foil, why would you
expect a change with copper foil?

Now, if you wrappped all the radio/tv/pager/cellphones in copper foil...
mike

"mike" wrote in message
newsdAZg.3099$3C6.2932@trnddc04...

Joey wrote:

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

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.

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

Is there some transmission which could be detected? Perhaps some low
power ultra high frequency from chip refresh cycles?

WEll, you could just stick an antenna up next to the player
and see.
This is what a sandisk looks like playing mp3s.
Can you tell which trace is of the sandisk?
Reading the title is cheating...
http://nm7u.tripod.com/homepage/nothin.jpg
http://nm7u.tripod.com/homepage/sandisk.jpg
mike