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Path: utzoo!utgpu!water!watnot!watmath!clyde!cbatt!ucbvax!hplabs!kitty!larry
From: larry@kitty.UUCP
Newsgroups: sci.electronics
Subject: Re: Stolen item-detectors (Was: Re: Laser eavesdropping)
Message-ID: <1698@kitty.UUCP>
Date: Sun, 12-Apr-87 10:05:30 EST
Article-I.D.: kitty.1698
Posted: Sun Apr 12 10:05:30 1987
Date-Received: Mon, 13-Apr-87 06:19:10 EST
References: <959@obelix.UUCP> <1104@nonvon.UUCP>
Organization: Recognition Research Corp., Clarence, NY
Lines: 26
Summary: Perhaps still just an LC circuit?

In article <1104@nonvon.UUCP>, apn@nonvon.UUCP (apn) writes:
> 	I visited the local music shop (Wherehouse) and after purchasing
> a tape, I disected the security device that was taped to the side. It 
> contained to foil plates mostly covered with paper with the exception
> of two small openings used as access to destroy the function of the
> device. Two wires each leaving one plate joined on opposite sides
> of a silicon die. Examining the silicon die under a occulars. It
> seemed to be only a simple diode and nothing more.

	Is it possible that what you thought to be a diode was in fact
an unencased "chip" capacitor?  If it were a capacitor, it would imply
that the detector element was just an LC circuit.
	The above device sounds to me like one of the detector elements
of a UHF theft-detection system which relies upon RF power absorption.
	While varactor diodes have been considered for use in the detector
elements of theft-detection systems as a frequency multiplier circuit,
it is my understanding that the cost of varactor diodes is still prohibitive
for such applications.  Most retail stores are _cheap_ when it comes to
spending money for items which do not directly attract business, so the cost
of most disposable theft-detection elements is << $ 0.15; if the cost were
much more, stores would not buy 'em.

<>  Larry Lippman @ Recognition Research Corp., Clarence, New York
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