Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!caip!clyde!cbatt!neoucom!wtm
From: wtm@neoucom.UUCP (Bill Mayhew)
Newsgroups: net.analog
Subject: Re: What is this device?
Message-ID: <272@neoucom.UUCP>
Date: Sat, 6-Sep-86 12:06:07 EDT
Article-I.D.: neoucom.272
Posted: Sat Sep  6 12:06:07 1986
Date-Received: Sat, 6-Sep-86 20:49:28 EDT
References: <38100001@gypsy.UUCP>
Organization: Northeastern Ohio Universities College of Medicine
Lines: 54
Summary: An antitheft gun...

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.

	While I haven't seen precisely the goodie you described,
I've seen similar ones.  The paper has some foil in it that serves
as a microwave frequency tank circuit.  When you walk out of the
store you pass through a microwave field (usually around 500 MHz).
The tank circut absobs energy, which lowers the voltage at receiver
on the opposite side of the door.  When the receiver detects a
voltage drop it usually switches on a camera to take your mugshot
and rings a chime at the counter.

	The little gun that the guy at the counter has sends a
current pulse through the foil to burn a hole in it.  Whith the
burnt foil, the resonant frequency of the tank is altered, thus
preventing the alarm from being tripped.  The beep is a continuity
test to verify that the circuit is open.  It would be rather
emberassing if the foil remained intact and a legitimate customer
got accidentally arrested.  The store could aslo be fined and/or
the cops would stop coming out after a number of false alarms.

	The industrious shop lifter could fool the scheme by
carrying a D-cell battery and some aligator clips to burn the foil
him/herself.  The tag could be removed from the package too, but
the icky glue used usually prevents quick removal, and assists in
the clerk spotting the removal attempt.  I certainly DO NOT condone
stealing anything, I just want you to be aware that the system is
not foolproof.

	I've seen a similar system used at the local equivalent of
K-Mart.  In this case they had the foil backed tags, but merely
stuck a second tag on top of the first at the check out counter.
The system had a bug, though as the glue on the appended tags made
them easy to peel off (and facilitate misuse by dishonest people).
The system must not have been very effective, as it was retired
only about 6 months after it went into operation.

  --Bill

Bill Mayhew
Division of Basic Medical Sciences
Northeastern Ohio Universities College of Medicine
Rootstown, OH  44272   USA    (216) 325-2511
(wtm@neoucom.UUCP)