What is the all clear siren?

The all-clear siren is a signal used to indicate that a previously hazardous situation, such as an emergency or disaster, has been resolved and it is safe for people to return to normal activities. It is often used in conjunction with warning sirens that alert the public to take cover or evacuate. The all-clear sound typically differs from warning sirens, making it easily recognizable. Its purpose is to provide reassurance and prompt a return to safety and normalcy.