What does the air defense alarm mean?

Generally speaking, it's a memorial, a drill and so on.

Xinhua Gansu Channel June 19 News According to Lanzhou Daily, June 20 is the trial day of air defense warning in our province. Lanzhou will conduct air defense warning trials in Chengguan District, Qilihe District, Anning District, Xigu District, Honggu District, Yuzhong County, Gaolan County and Yongdeng County from 9: 00 to 16: 00 on the same day. On June 18, Lanzhou Civil Air Defense Office held a press conference on "June 20" air defense alarm trial, reminding the general public to recognize and be familiar with signal types and maintain normal work, study, production and life order.

The trial sounding time of this air defense alarm is from 9: 00 to 16: 00 on June 20th. The specific time is as follows: at 9: 00 and 15: 00, a preliminary alarm will be issued. The standby alarm signal is: sound for 36 seconds, stop for 24 seconds, repeat for 3 times as a cycle, and the time is 3 minutes. Air raid alarms were issued at 9: 30 and 15: 30 respectively. The warning signal of air raid is: sound for 6 seconds, stop for 6 seconds, repeat 15 times as a cycle, and the time is 3 minutes. Disarm the alarm at 10 and 16. The warning signal is: continuous ringing for 3 minutes. (Reporter Ren Dejing)

(Lanzhou Daily)