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

My library has RFID tags (the stickers usually attached inside the cover) that uniquely identify all items. When you check it out the system then knows that specific item is borrowed and therefore to ignore it when it goes past the scanners.