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From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: net.analog
Subject: Re: What is this device?
Message-ID: <1245@kitty.UUCP>
Date: Wed, 3-Sep-86 23:02:03 EDT
Article-I.D.: kitty.1245
Posted: Wed Sep  3 23:02:03 1986
Date-Received: Sun, 7-Sep-86 20:21:20 EDT
References: <38100001@gypsy.UUCP>
Organization: Recognition Research Corp., Clarence, NY
Lines: 31
Summary: Shoplifting detection systems

In article <38100001@gypsy.UUCP>, rosen@gypsy.UUCP writes:
> I am curious if somebody might be able to explain to me what the following
> device is and how it works.
> 
> Recently I went to a record store and purchased a compact disk.  When I took
> the disk to the counter, the clerk turned it over and picked up a gun that
> had two small electrodes on the end of if it.  He pushed the gun against a
> small paper strip (about 1/2" x 2") that was attached to the outside of the
> CD box.  The strip was basically just a piece of paper that had two small
> holes in it where some silver foil was visible.  The two prongs on the gun
> contacted the foil in the strip through the two small holes and he then
> pressed a trigger on the gun and a beep was heard.  
> ...
> I knew immediate that this device was used to prevent people from leaving
> the store with the CD and by using the gun, he could 'disarm' the device so
> it didn't trigger the alarm when I left the store.  ...

	There are several shoplifting detection systems on the market, such
as Sensormatic, NoGo, etc.  Most of these systems use a tag which contains
a foil LC circuit which is resonant at one or more frequencies in the 2 to 10
MHZ band.  In simple terms, the detection devices function as a grid dip
meter with an alarm circuit; i.e., the presence of a resonant circuit in the
antenna field loads the transmitter oscillator by a minute amount - but yet
enough to activate an alarm.
	The gun which you described burned a fusible link in the foil LC
circuit, thereby disabling it.

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