Supermarket goods are generally equipped with two kinds of anti-theft devices, one is a small magnetic stripe, commonly known as "soft tag", and the other is a needle magnetic device, commonly known as "hard tag", both of which use the principle of magnetic induction to prevent theft. The alarm device at the entrance of the supermarket is also called "security door" and is equipped with a magnetic sensor. If the goods pass through the loss-proof door without degaussing, an alarm will be given. After customers choose goods and pay at the cashier, the cashier will degauss the goods with "soft labels" and "hard labels". If it is a "soft label", it will be demagnetized on the demagnetizer on the surface of the cashier. If it is a "hard label", special tools will be used to separate the "hard label" from the goods. In this way, the goods purchased by customers can safely pass through the "loss-proof door".