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PICList Thread
'anti-theft sticker'
1997\12\01@160151 by Jarek Pawlega

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I went to the bookstore, during my lunch break today
and I bought a book. There was a plastic sticker on the
book, with a bar-code on it and two isolated strips
of metal inside the sticker.

As soon as the bar-code is scanned the anti-theft
gate doesn't 'care' the sticker, assuming, the good was
paid. Otherwise, carrying the book through the gate will cause
activating the alarm system.

We all used to see them, almost everywhere.

Does anyone of you, gentlemen, know, how this
system is called, how the sticker 'works' ?

I guess, it might be some kind of resonant / absorbing
device, those two strips of metal are acting like
but I can't believe it is addressable 'by sticker'.
It should require very high accuracy.


Regards,
Jarek


p.s.
Of course, I'm not going to still anything. Except some knowledge.

1997\12\01@162925 by John Shreffler

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part 0 1522 bytes
In some systems there is a diode between the metal foil
patterns which act as an antenna to pick up 2 GHz
radiation, and reradiate back a lot of harmonics, which
in turn are picked up by the alarm receiver.  The device
is defanged by applying a pulse that destroys the
diode.

But I have also disected some tags that are slipped into
the binding of library books, that seem to be only a
couple of parallel foil strips, no diode.  I can't imagine
how they work, but would also be interested if anyone
has the answer.

John
{Original Message removed}

1997\12\01@163001 by Andrew Mayo

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It is a resonant circuit, which is triggered by a transmitter in the
doorway. By passing a strong magnetic field over the device, it can be
deactivated - I am not quite sure how this works but I think what
happens is that part of the strip is ferromagnetic. If it is magnetised,
it affects the resonant circuit, either by changing the frequency or
introducing harmonic distortion.

Some variant devices use (I think) a small low-signal diode which is
destroyed by an electromagnetic pulse - until this is done passing the
circuit through the door will generate a strong second harmonic signal
which will trigger the alarm.

{Quote hidden}

1997\12\01@165333 by Martin R. Green

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On Tue, 2 Dec 1997 10:25:07 +1300, Andrew Mayo <andrewspamKILLspamGEAC.CO.NZ>
wrote:

>It is a resonant circuit, which is triggered by a transmitter in the
>doorway. By passing a strong magnetic field over the device, it can be
>deactivated - I am not quite sure how this works but I think what
>happens is that part of the strip is ferromagnetic. If it is magnetised,
>it affects the resonant circuit, either by changing the frequency or
>introducing harmonic distortion.
>
I have dissected some of these and found a small printed metallic
coil, which I presume is part of that resonant circuit.
>
>Some variant devices use (I think) a small low-signal diode which is
>destroyed by an electromagnetic pulse - until this is done passing the
>circuit through the door will generate a strong second harmonic signal
>which will trigger the alarm.
>
Gee Whiz - does this mean I could defeat these things by carrying a
small EMF pulse generator, such as an electric butane BBQ starter
wand?  ;-)

CIAO - Martin.

Martin R. Green
.....mrgreenKILLspamspam.....NOSPAMbigfoot.com

To reply, remove the NOSPAM from the return address.
Stamp out SPAM everywhere!!!

1997\12\01@170611 by Alberto Smulders

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Jarek,

Take a look at

          http://patent.womplex.ibm.com/

and see patents (among about 100 others) 5,300,922 - 5,574,431 - 4,413,254
- 4,622,542 - 3,983,552 - 4,074,249 - 3,820,104 - 4,063,229 - 4,993,245 -
5,572,191 - 5,008,649 - 3,895,368 - 5,510,770 - 5,300,922.......

and I think you'll know everything about how the whole security-tag stuff
works....

Albert Smulders
InSAD - Encarnaci—n, Paraguay
EraseMEinsadspam_OUTspamTakeThisOuTitacom.com.py

1997\12\01@221327 by Mroczkowski

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<snipsnipsnip>
Gee Whiz - does this mean I could defeat these things by carrying a
small EMF pulse generator, such as an electric butane BBQ starter
wand?  ;-)

CIAO - Martin.

Martin R. Green
mrgreenspamspam_OUTNOSPAMbigfoot.com

To reply, remove the NOSPAM from the return address.
Stamp out SPAM everywhere!!!
=================
Actually, they are deactivated by a pulse that "burns them open"...something
a B-B-Q starter would be hard pressed to produce;^))

Simply covering the patch with a piece of aluminum foil will render it
inoperative.

-Cheers, Hank

1997\12\02@084627 by David Anderson

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There are three types of theft detections systems I'm aware of. The kind
that requires a sticker and is a resonant circuit is made by a company
called CheckPoint. The sticker has a metal foil resonant circuit tuned to a
specific frequency. The detectors are tuned to a specific frequency, so
little else will set them off. I worked in a library that used the
checkpoint system. We had special due date cards that went in the pockets
to "deactivate" the sticker. The cards themselves had a sheet of foil
embedded inside. You'll see the checkpoint sticker most often in the pocket
of a book. In commercial applications, it may be disguised as a UPC. A tear
in the circuit is usually enough to deactivate it (razor or simply rip some
of the sticker off).

The other major system in use, especially in libraries, is the 3M
Tattletape. These are thin strips about 3-5" long and about 1/8" wide. They
are magnetically deactivated, so a strong magnet will detune them. Of
course, so will pulling out the Tattletape. The most common location for
tattletape is in the spine, so the book can be slid along its spine in the
desensitizer. The tattletape is also used a lot in cd stores.

The third I've only seen in retail. It's a small plastic strip about 1 1/2"
long, 1/2" wide and 1/16" high. It's also magnetically desensitized, based
on the desensitizer's I've seen. Ripping the sticker off seems to be the
only safe approach.

{Original Message removed}

1997\12\02@113253 by John Payson

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> The third I've only seen in retail. It's a small plastic strip about 1 1/2"
> long, 1/2" wide and 1/16" high. It's also magnetically desensitized, based
> on the desensitizer's I've seen. Ripping the sticker off seems to be the
> only safe approach.

Isn't a somewhat safer approach to hand the item to the person sitting near
a machine with lots of buttons on top and a money drawer underneath?  Prefer-
ably with a bribe in an amount typically marked on the item in question?  I
have found this approach to be 99.9% reliable in ensuring that the alarm does
not go off, and I have also found the store personnel to be quite friendly and
apologetic on those occasions when the alarm has tripped.

While your approach might have similar reliability at avoiding the alarms, I
doubt the personnel would be as friendly on those occasions when the alarm
sounds.

1997\12\02@154403 by Wim E. van Bemmel

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Hear! Hear!

John Payson wrote:

{Quote hidden}

--
Regards,

Wim
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 Netherlands
 @spam@bemspanKILLspamspamxs4all.nl

 ... Life is about Interfacing .....
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