Most of the alarms in bookstores use Acusto magnetic system.
This is a physical principle, similar to the vibration of a tuning fork. Using this principle, almost zero false alarm can be achieved.
When the tag of the acousto-magnetic system fixed on a commodity or affixed to a book enters the detection area of the system, it will generate * * * vibration, but it will give an alarm only after the receiver receives the * * * vibration signal for four consecutive times (once every 1/50 seconds).
The device will respond to this magnetic tag, but in the past, people or paper certainly did not respond. Moreover, the magnetic needles used in books are generally small, and it is difficult for customers to find and take them out. Some expensive books are directly built in when binding, and can only be removed by degaussing equipment when checking out.