-----BEGIN PGP SIGNED MESSAGE----- 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
In our school library, there is a depository area wherein you deposit your
At 09:52 PM 7/12/96 +0800, you wrote: 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:
------ / \ Š--ŠŠ--Š \ / ------
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 -----BEGIN PGP SIGNATURE----- Version: 2.6.2 iQEVAwUBMemW+TAJap8fyDMVAQE8vQf/U1Pfx2ejbkz8bVN1swVG3nVZGOmh5PGM GdIG4ON2/hSOF8Ex9qJTSHvbLaJGCQnNnZhMGIrB4Y+S3qT7FyqPAfKBBMreLgNm oV+yZdqwdyh7wRQnC9iXL8VLvBQTC1UjrwDq/47Os3j7s1gx2HVulvX3afG+Am7U SlRnWxaYIkJADSAoevKE5Y1fv1GClDwA5cWmT1b9Y2T/wV0hj5YiP1pNMaAlPzBF vmQelyA2Fo2zKPIUaFgEuYCde5jEQMaozmx+aladj6COc7vvGGiCa1mhSc9UZAum lBpHKQ+NKPLOl7ovZk3rnrg+Z03kaHkvxRbhzuuveBaS2RxZBSUsGw== =1BcU -----END PGP SIGNATURE-----