"Alexander Grigoriev" wrote in message
ink.net...
It all boils down to a weapon vs armor arms race.

Suppose one vendor produced a device that can detect some device which
samples at 8 kHz. More likely it will detect frequencies that are multiple
of 8 KHz. Then, an MP3 recorder doesn't have to use any external xtal
frequency which is n*8000 - an on-chip PLL is commonplace. A mic is
connected directly to the chip, so it won't give any EMI.

Most reliable signature would be periodic access to the flash serial
interface, though.

Still, if someone wants to record a conversation, undetected, a custom
shield may be manufactured for the recorder (like 1 mm of permalloy/copper
sandwich), and bingo: no detection.


Right it's a secret part of an "arms race", but the same
lab(s) are developing surveillance equipment and counter-
surveillance equipment. With unlimited funding, you can
have your "Undetectable Device" and you can have a
Device to detect the undetectable. It becomes what you
can have at what cost and in what numbers. The more
expensive and rare devices are reserved for the most
sensitive and vital situations.

It is in the interest of those working the counter-surveillance
side, that those thinking of using a surveillance device, not
know the likelihood of their being an effective detection
device in play or not. Things electronic get cheaper all the
time, last year's rare laboratory sensor may well be in next
year's field unit.

Luck;
Ken