How do those walk-through scanners in libraries know if you’re taking a book without borrowing it, especially if those books don’t have metal inserts or anything like that?

Question

How does the library borrowing system work? and how come even if there is no obvious metal insert in the book those gates still know when and when not to beep if the book has or hasn’t been borrowed?

In: Technology

Answer 1

In highschool i took the security tags out of a few xboxgames i got at the bargain bin and i stuck them under the cart for the projector, and for a few weeks every time someone rented a projector the alarms would go off