mb@sparrms.ists.ca (Mike Bell) (05/09/91)
Further to the discussion of library anti-theft tags, I recently
took to pieces a store anti-theft tag, and I'm stuck on how this
one works:
It consists of a rather bulky plastic self-adhesive package, about 40mm
x 13mm. Inside are two mettalic strips. One is a rectangle 38mm x 12.2
mm. The other is a parallelogram:
__________________
/ / ^
/ / |12.2mm
/_________________/ |
< 29mm >
The angle is 45 degrees. All dimensions are +/- 0.25mm
The two strips are separated by a plastic membrane.
Anybody able to explain the principle of operation?
What are the relevant frequencies of operation?phil@ux1.cso.uiuc.edu (Phil Howard KA9WGN) (05/10/91)
The ones used in a local store are not angled, they are square. The layers are separated, but there is an indentation at a couple of points to "connect" the metallic layers. They form a capacitor and inductor (the spiraling metal lines). I have no idea what the frequency is. I don't have a generator to set this with. There are several frequency ranges the FCC has authorized for motion detectors. -- /***************************************************************************\ / Phil Howard -- KA9WGN -- phil@ux1.cso.uiuc.edu | Guns don't aim guns at \ \ Lietuva laisva -- Brivu Latviju -- Eesti vabaks | people; CRIMINALS do!! / \***************************************************************************/
cyborg@kauri.vuw.ac.nz (Alex Ivopol) (05/10/91)
While on this topic, I saw an interesting device as well. It is disguised as a price tag sticker. Once stuck on something it is very difficult to tell it is more than that. Inside there is a spiral made of a narrow strip of thin aluminium foil. The spiral is made of straight segments that bend at 90 deg angle and has about 20 turns, the whole thing is square in shape. The outer arm of the spiral ends in a much thicker (rectangular) strip. A thin insulating foil is placed on top of this with a small hole just on top of the start of the inner arm of the spiral. Another narrow strip of aluminium foil is placed on top of the insulating foil, this strip contacs the inner arm of the spiral, runs across the turns and ends in a thick rectangular shape, just on top of the other rectangle beneath the insulating foil. This whole arrangement looks very much like a capacitor in parallel with a coil Don't ask me how it works tho... I realize that this would most probably resonate in an electromagnetic field of the right frequency, but how does one disable it once you bought the product and go out the shop through the gates ? The sticker is diposable and stays on the merchandise once you bought it. The salespersons do not do anything funny with the products (like placing them briefly under the counter) before handing them back to you... -- Alex T. IVOPOL cyborg@kauri.vuw.ac.nz
pwh@bradley.bradley.edu (Pete Hartman) (05/10/91)
In <1991May10.003238.24277@comp.vuw.ac.nz> cyborg@kauri.vuw.ac.nz (Alex Ivopol) writes: [ description of sticker device to foil shoplifters ] >This whole arrangement looks very much like a capacitor in parallel with a coil >Don't ask me how it works tho... I realize that this would most probably >resonate in an electromagnetic field of the right frequency, but how does one >disable it once you bought the product and go out the shop through the gates ? >The sticker is diposable and stays on the merchandise once you bought it. The >salespersons do not do anything funny with the products (like placing them >briefly under the counter) before handing them back to you... I don't remember precisely, but I took one of these apart some time ago, and noticed that there was a puncturing of some sort that shorted the capacitance. I don't recall quite how it was produced, but it was clearly not there in the store. -- ----- Pete Hartman Bradley University pwh@bradley.bradley.edu
tonya@hpldsla.sid.hp.com (Tony Arnerich) (05/11/91)
I dissected one of these gizmos that was on a CD box. It has two curved elements (antenna?), an hourglass detail that was blistered at the junction (burned out fuse for disabling), two exposed circles of circuit trace (connection to disabling wand?) and a VERY tiny silicon chip. There were two wires going into the chip, so I figured that it might be a diode. Under a microscope (this thing measured only about 0.2mm on a side!), there did not appear to be any complex circuit pattern. The overall dimensions on the "antenna" are about 3/4" by 5". tonya@sid.hp.com
whit@milton.u.washington.edu (John Whitmore) (05/14/91)
In article <1990021@hpldsla.sid.hp.com> tonya@hpldsla.sid.hp.com (Tony Arnerich) writes: >I dissected one of these gizmos that was on a CD box. > >It has two curved elements (antenna?), an hourglass detail that was >blistered at the junction (burned out fuse for disabling), two exposed >circles of circuit trace (connection to disabling wand?) and a VERY >tiny silicon chip. There were two wires going into the chip, so I figured >that it might be a diode. With either a varactor or a PIN diode, this could easily be a frequency doubler/tripler; send out an interrogation pulse and look for a triple-the-frequency response, and you've located a tag that hasn't been disabled. At a guess, the curved elements would be resonant at the interrogation frequency and the tripled frequency, respectively. John Whitmore
fmgst@unix.cis.pitt.edu (Filip Gieszczykiewicz) (05/14/91)
Greetings. I've seen 20+ posts on people taking security devices apart - what I'm wondering is where did they get them.... ;-) Take care. P.S. Thank you to all the people who replied to my post on the couple SIP power amps that I posted a few days ago. -- _______________________________________________________________________________ "The Force will be with you, always." It _is_ with me and has been for 11 years Filip Gieszczykiewicz "... a Jedi does it with a mind trick... " ;-) FMGST@PITTVMS or fmgst@unix.cis.pitt.edu "My ideas. ALL MINE!!"
lou@caber.valid.com (Louis K. Scheffer) (05/15/91)
cyborg@kauri.vuw.ac.nz (Alex Ivopol) writes: >While on this topic, I saw an interesting device as well. It is disguised as >a price tag sticker. Once stuck on something it is very difficult to tell it >is more than that. >Inside there is a spiral made of a narrow strip of thin aluminium foil. The >spiral is made of straight segments that bend at 90 deg angle and has about 20 >turns, the whole thing is square in shape. The outer arm of the spiral ends in >a much thicker (rectangular) strip. A thin insulating foil is placed on top of >this with a small hole just on top of the start of the inner arm of the spiral. >Another narrow strip of aluminium foil is placed on top of the insulating foil, >this strip contacs the inner arm of the spiral, runs across the turns and ends >in a thick rectangular shape, just on top of the other rectangle beneath the >insulating foil. Assuming this is the gadget I'm familiar with: There is a diode in between the coil and the capacitor. When you hit it with microwaves, you get back second harmonic due to the non-linearity of the diode. When you buy the product, the cashier zaps the diode with a small gun like tool - then you get no second harmonic, and no alarm. -Lou Scheffer-
luns@spocom.UUCP (Luns Tee) (05/16/91)
cyborg@kauri.vuw.ac.nz (Alex Ivopol) writes: > This whole arrangement looks very much like a capacitor in parallel with a co > Don't ask me how it works tho... I realize that this would most probably > resonate in an electromagnetic field of the right frequency, but how does one > disable it once you bought the product and go out the shop through the gates > The sticker is diposable and stays on the merchandise once you bought it. The > salespersons do not do anything funny with the products (like placing them > briefly under the counter) before handing them back to you... > > The local library uses the same sort of stickers on their cassettes. I haven't found anything in the books and magazines though. They get around things by passing books around the detector. As for disabling them, some stores have bins in which the cashiers fill your bags with sold goods. I'd suspect these bins to also be degaussers.