Why is there a detector at the entrance of the library? What can the detector detect? Can a bigger metal or magnet make it react?
Generally, there are magnetic strips in books, and this detector is used to detect this. I remember that in my Xinhua Bookstore, the magnetic stripe was on page 23 or so. Under normal circumstances, if you take off this magnetic stripe, the book taken out privately will not be detected. But this is not authentic, it's too out of tune.