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From: apn@nonvon.UUCP
Newsgroups: sci.electronics
Subject: Re: Stolen item-detectors (Was: Re: Laser eavesdropping)
Message-ID: <1104@nonvon.UUCP>
Date: Sat, 11-Apr-87 18:06:16 EST
Article-I.D.: nonvon.1104
Posted: Sat Apr 11 18:06:16 1987
Date-Received: Sun, 12-Apr-87 06:08:36 EST
References: <959@obelix.UUCP>
Organization: NONVON Systems Computer Research Group
Lines: 32

in article <959@obelix.UUCP>, per-el@obelix.UUCP (Per Elmdahl) says:
> 
> 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.....
> 
> Does anybody have other theories, or doues anybody know how this works?
> 

	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.

	I   should have placed the entire device in an RF cavity and
measured absorptions at RF with a network analyzer ... but it was already
in a destroyed stayed upon leaving the store. Maybe next one....... 

Alex P Novickis

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{* Only those who attempt the absurd   ...   will achieve the impossible   *}
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