rosen@gypsy.UUCP (09/02/86)
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 USENET: adrvax\ ihnp4 | princeton |-->!siemens!gypsy!rosen topaz | vrdxhq/ ARPA: siemens!gypsy!rosen@topaz.rutgers.edu
larry@kitty.UUCP (Larry Lippman) (09/04/86)
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 ==> UUCP: {allegra|decvax|rocksanne|rocksvax|watmath}!sunybcs!kitty!larry ==> VOICE: 716/688-1231 {hplabs|ihnp4|seismo|utzoo}!/ ==> FAX: 716/741-9635 {G1,G2,G3} "Have you hugged your cat today?"
wtm@neoucom.UUCP (Bill Mayhew) (09/06/86)
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)
GOT@PSUVMA.BITNET (09/06/86)
many libraries use similar devices to prevent theft of books. My guess
is that the sensors at the doors detect the distance between small
metallic squares embeded in the strip. The squares must be magnetized
in order to be detected.
its just speculation...
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charles@c3pe.UUCP (Charles Green) (09/08/86)
In article <272@neoucom.UUCP> wtm@neoucom.UUCP (Bill Mayhew) writes: >In article <38100001@gypsy.UUCP>, rosen@gypsy.UUCP writes: > 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. > > 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. That sounds like the same thing our local library has started doing. While I volunteered there, we had to put little tags on all the reference books; being a technically-minded sort, I couldn't help but notice the coil on the sticky side. We also have rather conspicuous person-high structures which are responsible for setting off alarms as people go through. In addition, some of the books that are checked out have the traditional pocket in which a dated card is slipped by the checkout person, but with a twist: the pocket has the coil inside it, and the card is made of some sort of blocking material, probably similar to the "second tag" described above. Makes more sense than burning the coil, since they have to be reusable. -- "No! Wait!! ''To Serve Man''... it's a *cookbook*!!!" -Charles Green at C3 Inc. {{styx!seismo,cvl}!decuac,dolqci}!c3pe!charles _____-__---__-_----_-__-_-_----__-_--_--___-_---__-__-_-_-_--__-_-__--___-_____