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From: rosen@gypsy.UUCP
Newsgroups: net.analog
Subject: What is this device?
Message-ID: <38100001@gypsy.UUCP>
Date: Tue, 2-Sep-86 12:44:00 EDT
Article-I.D.: gypsy.38100001
Posted: Tue Sep  2 12:44:00 1986
Date-Received: Wed, 3-Sep-86 05:13:53 EDT
Lines: 45
Nf-ID: #N:gypsy:38100001:000:2115
Nf-From: gypsy!rosen    Sep  2 12:44:00 1986



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.  The gun was apparently
wired to the cash register or some other device near the cash register
(where the beep came from).

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.  I have seen other
versions of this "Knowgo" (I think that is one of the trademark names), but
usually they were bulky devices removed at the point of sale and found
mostly in clothing stores.  I thought at first that this device might
consist of a highly expendable microchip embedded beneath the paper strip
with the foil acting as a pair of contacts.  When I left the store I
examined the device more closely and tried to separate the foil from the
paper, but I did not find anything else except a piece of foil embedded
between two pieces of paper.  Actually I couldn't easily separate it, but
that was all it appeared to be.

This device was very puzzling to me.  Can anyone explain to me how this
whole system (the tag and the alarm) work together.  I am mostly interested
in the tag itself and would be curious to know exactly what it is.

----------------
| Steve Rosen
| Siemens Research and Technology Laboratories
| Princeton, NJ

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