In order to prevent the goods from being stolen, merchants usually put anti-theft labels on the goods. This label is self-adhesive and can be attached to goods. There is a magnetic ring on the adhesive surface, and the front of the label looks like an ordinary bar code.

When goods with anti-theft labels go to the cashier to check out, the cashier first scans the barcode of the goods, and then degausses the anti-theft labels, so that the goods you take out will not have an alarm. If the cashier has scanned the bar code to collect money but forgot to degauss it.

When you walk to the door, you will call the police, so the alarm does not depend on the bar code of the product, nor on the product itself, but on whether the anti-theft label is degaussed.

Anti-theft device in supermarket

Supermarket goods are generally equipped with anti-theft devices. This small magnetic stripe, commonly known as "soft tag", uses 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. The reason is that if the cashier negligently degausses and fails to remove this small "soft label" after the family buys pants and pays with WeChat, the customer will be "shot while lying down".