A hand crank air raid siren is a type of mechanical siren that is activated by turning a crank handle. It is typically used as an emergency warning device, such as in the event of a natural disaster or an air raid during wartime. The siren produces a loud, piercing sound that can be heard over a long distance, alerting people to take cover or evacuate the area. Hand crank air raid sirens are portable and can be easily moved to different locations as needed. They are often used by first responders, such as firefighters and police, as well as by military personnel.