what is that thing librarians use when you checkout a book?

what is that thing librarians use when you checkout a book?
I went to the library today, and it seems to me that every time i go the librarian scans the book with the barcode lazer thing, then she would like rub it on some random stone looking thing on the counter. Its not plugged in or anything, and there isnt any hardware inside books…so what the heck is this thing for?
thanks alot man good answer

Best answer:

Library books have small magnetized strips on them, located either in the barcode tag or along the spine. That “stone thing” de-magnetizes the book so that the alarms don’t go off when you leave.

If you have a self-checkout machine, you’ll notice that in order to put the book under the scanner, you’re forced to slide them along a de-magnetizer as well.

Tags: Book, checkout, librarians, thing

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