How do shops use door magnetism to prevent theft?

Door magnetic alarm is most suitable for bungalow smoking hotels. This cheap alarm device is very effective and can effectively stop thieves who try to sneak in through the window. However, because the door magnetic alarm will only give an alarm when the door is opened, if the owner happens to be out of the store at this time, more effective measures can not be taken to prevent the thief who left in fear from entering the house again. One is attached to the door or window leaf, and the other is attached to the door frame or window frame, but the two must be very close. Under normal circumstances, when the doors and windows are closed, the magnets and springs are closed; when the doors and windows with door magnetism are illegally opened, the magnets and springs are separated, and the spring shrapnel bounces off to generate a switch signal which is input into the drive chip to drive an external alarm to give an alarm.