An alarm is an electronic product that reminds or warns us that we should take certain actions in the form of sound, light, air pressure, etc., in order to prevent or prevent the consequences caused by an event. Alarms are divided into mechanical alarms and electronic alarms. With the advancement of science and technology, mechanical alarms are increasingly being replaced by advanced electronic alarms. They are often used in the fields of system failures, safety precautions, transportation, medical rescue, emergency response, induction detection, etc., and are closely related to social production. Indivisible. Such as: door magnetic sensor and gas sensor alarm.