The anti-theft magnetic stripe of books in the library, some books bought in bookstores also have the same anti-theft magnetic stripe, so when you cross the detector, the detector will give an alarm, so it is not enough to just remove the barcode of the book. You need to take out the anti-theft magnetic stripe, but the location of the anti-theft magnetic stripe in each library book may be different, so it's hard to say where it is. I suggest you either find the magnetic stripe or don't take the book to the library.