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Re: Demagnetizing

At 04:26 PM 8/27/95 -0500, Buford Terrell wrote:
>>Reply-To: [email protected] (Tobin T Fricke)
>>Where exactly is the r/c circuit?  Is it very small and in
>>a label?  Book publishers don't put them in, do they?  
>>Also, if the thing gets "burned out" by the magnet in the
>>pad, what do libraries and such do where materials are
>>reused?  Just slap on another label thing?  
>It's much more low-tech than that.  Libraries and book stores just
>put a strip of magnetized material (it's much like audio tape,
>about 1/8 inch wide and comes on rolls) inside the book and then
>put detectors at the doorway.  It the detector feels a magnetic field,
>it buzzes; if the tape has been deguassed, nothing happens.
>For libraries, it's usually mounted on sticky tape and put down
>inside the book spine.  Bookstores usually just snip off a 4 - 5"
>segment and slip it inside the book.  Music stores frequently tape
>a small section on the outside of CD jewel boxes.
>Sorry, there's no real mystery or exciting tech here.
There's still some mystery.
For instance, how does it differentiate between the magnetic
field of their strip, and the magnetic field of the strip on your
credit card, or the speaker on your cell phone?