Re: anti-theft strips

[Roger Haar <haar@PHYSICS.ARIZONA.EDU>]

Hi,
        There is a 1 page article inside the back cover of the May 97
Scientific American about these things.

        The dsecription goes like this.  The door unit transmits a pulsed
58 kHz radio.
signal.  The antishoplifting stickon contains a resonator made of a
magnetic material the right size to mechanically vibrate at 58 kHz.  The
vibrating resonator produces its own 58 kHz radio signal.  So, the pulse
from the door unit starts the device vibrating, the pulse stops, and then
the door unit looks for a 58kHz signal.

Thanks
Roger Haar
*****************************
Leon Leonardo wrote:

> Perhaps it's classified information, but just between you and me:
>
> Anyone out there know just how those anti-theft strips that are often
> inserted in books, or attached to CDs. etc, work?  I've taken a few
> apart, both inside and outside the store, and found they are all what
> appears to be a very small capacitor with one obviously metal plate,
> and the other plate, well, at least it is metal like.  Electret?  In
> anycase, if they are tightly squeezed together (the plates, that is)
> they don't work.
>
> Particulaly, how is it that they are so easily desensitized?
>
> Note: this is a strictly academic query.
>
> Leon
>
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