What is that thing in the library where they rub the binding against?

Question

Like its made out of metal and they slide the book binding against it before they give me the book. What does that do?

Answer 1

You can get these little strips that you put between 2 of the pages of a book. (they are only 5mm wide approx). They are like electronic tags. Does your library have alarms by the door? If it does then this is what they are for.

Basically, if you take a book out of the library and it hasn't been slid across the metal thing then the alarms will go off. The metal thing de-activates the strip so that when the librarian knows who has got the book, the person is free to go. The alarms wont go off if the strip has been de-activated. It is just a way of stopping people stealing the books.