What triggers the alarm of a library?

What triggers the alarm of a library?
I was just curious at what part of the book actually causes the exit of the library to go off, people tell me its the barcode, but I think that if someone were to steal a book then all they have to do is rip the barcode right? I know its not that easy, but does anyone know exactly what causes the alarms to go off?

Best answer:

A device called a ‘tattle tape’ which is a sticky strip with a magnetic socket in it, (its basically a thin flat wire), is put down the book spine or inside one of the pages. When trying to get through the gate way at the library door the alarm will set off if the magnetic strip has not been ‘desensitised’ (Checked out).

Sometimes you can spot them, other times you can’t. Green tattle tapes are used in paperback books whilst white are used in hardback books.

Tags: alarm, library, triggers

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