Where did the air raid alert come from?

The air defense alarm is issued from the horn in the siren of the air defense alarm equipment.

Among them, alarms are divided into three types: electric alarms, electric alarms, and hand alarms. The electric siren uses a motor as the main component of the siren, converting electrical energy into sound; the electroacoustic siren is composed of a host amplifier and a speaker; the hand-cranked siren is a supplementary warning device for the electric siren and the electroacoustic siren.

Extended information:

Air defense warnings are divided into three types: advance warning, air raid warning and clearance warning.

1. Pre-alarm: sound for 36 seconds, stop for 24 seconds, and repeat 3 times as a cycle, lasting 3 minutes. Citizens quickly evacuated to nearby underground air raid shelters, civil air defense projects and air raid shelters.

2. Air raid siren: sound for 6 seconds, stop for 6 seconds, and repeat 15 times as a cycle, lasting 3 minutes. Citizens took advantage of the terrain and features to hide nearby, lying on the ground and holding their heads in their hands.

3. Clear the alarm: After a long beep for 3 minutes, citizens can walk out of underground air raid shelters, civil air defense projects and air raid shelters and resume normal work.

Baidu Encyclopedia-Air Defense Alert