From: The Deviant <deviant@pooh-corner.com>
Date: Mon, 15 Jul 1996 12:56:08 +0800
To: Remo Pini <rp@rpini.com>
Subject: Re: Stuffs used for detection
In-Reply-To: <1.5.4.32.19960714164618.008c35ac@193.246.3.200>
Message-ID: <Pine.LNX.3.94.960715005051.214A-100000@switch.sp.org>
MIME-Version: 1.0
Content-Type: text/plain


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On Sun, 14 Jul 1996, Remo Pini wrote:

> Date: Sun, 14 Jul 1996 18:46:18 +0200
> From: Remo Pini <rp@rpini.com>
> To: cypherpunks@toad.com
> Subject: Re: Stuffs used for detection
> 
> At 09:52 PM 7/12/96 +0800, you wrote:
> >In our school library, there is a depository area wherein you deposit your
> things and get the tag. Since the library doesn't allow those tags to be
> brought out from the library, everytime you brought it out and pass by the
> door, it will alarm. Does anyone know what stuff is that? How come it is
> alarmed? I brought some metals but it wouldn't alarm... Why those tag would
> alarm them???
> >
> 
> Most of these systems are made of an oszillator (basically a few windings of
> a wire with a capacitor:
> 
>  ------
> /      \
> ¦--¦¦--¦
> \      /
>  ------
> 
> This acts like an ordinary RLC-Oszillator. When you put it in a electrical
> field with the right frequency, it will effect the field strong enough to be
> detectable.
> 
> So, if you shield it, you win.
>

The other type of those, the one that is used in music stores on CD's, is
done slightly (much) differently...

they use two peices of metalic foil shaped like this....
______
|     \
|______\

pointed in opposite directions, so as to look like this

_________
\ |      \
 \|_______\

when magnatized the two peices stick together, and will reflect a signal
on a harmonic of a specific wavelength of sound (the length of the total,
so that if they're not magnatized it won't reflect to the right
frequency), thus being easily detected.

these are actually fairly easy to fake or get past ;)

 --Deviant


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