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

Probably the same as retail stores sticking their security tags on things. The tags themselves look like barcodes but underneath them there is a magnetic strip. They probably dont have barcode like tags but the idea is the same.