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Path: utzoo!utgpu!water!watnot!ccplumb
From: ccplumb@watnot.UUCP
Newsgroups: sci.electronics,sci.physics
Subject: Stolen-item detectors (Was: Laser eavesdropping)
Message-ID: <12813@watnot.UUCP>
Date: Tue, 7-Apr-87 10:49:11 EST
Article-I.D.: watnot.12813
Posted: Tue Apr  7 10:49:11 1987
Date-Received: Thu, 9-Apr-87 03:43:59 EST
References: <16143@sun.uucp> <2632@phri.UUCP> <1683@kitty.UUCP> <2634@phri.UUCP>
Reply-To: ccplumb@watnot.UUCP (Colin Plumb)
Organization: U. of Waterloo, Ontario
Lines: 26
Keywords: modulation
Xref: utgpu sci.electronics:468 sci.physics:1061

In article <2634@phri.UUCP> roy@phri.UUCP (Roy Smith) writes:
>	This is also, BTW, one of the ways those stolen-item detectors in
>stores work.  The big plastic clips contain some sort of passive tuned
>circuit, with a diode detector.  The gizmos on either side of the door emit
>RF at some frequency (presumably up in the several hundred Mhz range) and
>listen for harmonics comming back.  The important features of this system
>are that the replicated parts (the big plastic clips) 1) are cheap to
>produce, 2) require no internal power, 3) are not likely to break, and 4)
>can be made physically small.  The latter three are properties which also
>makes this a nice spy technology.

I always wanted to know that.  I've seen thing with a similar purpose at
bookstores.  They looked like strips of aluminized mylar/tinsel, a few inches
ling and about 7mm wide.  They can be `turned off' (so they don't register to
the thing at the exit) by a demagnetizer-like gizmo.

Anybody know how these work?

(Funny thing: one store I know has one of these, but they always leave it
turned off!  Kinda ruins the effect if the power lights and switch are
visible, don't it?)
--
	-Colin Plumb (watmath!watnot!ccplumb)

Silly quote:
That's a horse of a different feather.