In order to prevent stealing books, bookstores usually bring metal strips inside the books.

It is the electronic anti-theft system of a bookstore or library, which is specially used to attach metal bars to books. Some books can't see the iron bars, so they are probably not installed or installed at the back. Libraries and bookstores not only rely on this iron bar to guard against theft, but also cameras, administrators and salespeople. This iron bar is just an auxiliary thing.