sirens are generating sound to provide warning of approaching danger and sometimes to indicate when the danger has passed.such as when there is a very high risk of military conflict, sirens will blare to warn the public of possible attacks or invasion

there is 4 alert signal

1.Red Alert (attack imminent)

the Signal switch on for 6 seconds and off for 6 seconds,repeat 15 times as a circle,with  3 minutes wavering siren tone

2.Yellow Alert (attack likely)

the Signal switch on for 36 seconds and off for 24 seconds,repeat 3 times as a circle,last 3 minutes

3.White Alert (all-clear)

with  3 minute steady continuous siren tone

4.Blue Alert (undefined)

 it could be achieved by holding the Signal switch on for ( )seconds and off for (  )seconds to manually generate the warbling tone