All the books in Xinhua Bookstore have magnetic stripes, which are embedded in them before they are put on the shelves. Because of the double-sided tape, it is generally invisible. This kind of magnetic stripe is made of metal, and every book is the same. Security doors can only find books, but they can't tell what books they are. When paying, the book should be placed on something the size of a mouse pad, that is, a degaussing machine. When degaussing, the book is still hot. It is demagnetized by the principle of heating. If your book has no magnetic stripe or a non-magnetic magnetic stripe, the security door will not respond. Like books in the school library, they are usually posted on page 100. This is convenient for inspection.