Hand Cranked Air Raid Sirens of the 1940s

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We are fortunate to have never heard this sound. Hand-cranked air raid sirens were portable warning devices used in the 1940s to alert the public of air raids. By cranking the handle, the rotor spins, creating an airflow that passes through the stator’s holes, where it is rapidly interrupted to produce a vibrating sound wave. Even a small hand-cranked siren could reach over 120 decibels, making it an effective warning system even without electricity. A rising and falling tone signaled an imminent attack, while a steady tone indicated that the danger had passed.
Credit: toysgadgetscollectibles9087 / YT, TheSirenManiacYT , MichelleFiskilis / YT, walkamongheroes / YT, merrytools4049/ YT, soundsofchanges7145 / YT

#technology #history #ww2