Civil defense

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[edit] Warning the population in case of a coming disaster

Beginning of the alert: the sound warning is made of three sequences of sound going up and down lasting one minute, separated by a silence lasting five seconds. End of the alert: continuous signal of 380 Hz, lasting thirty seconds.
In case of a signal generated by electronics, a cycle is made of a two second rise from 300 Hz to 600 Hz, then a two second decrease back to 300 Hz; in case of an electromechanical siren, a cycle is made of seven second where the motor is on (the sound rises to 380 Hz), then five seconds where the motor is shut down.