Air Horn

An air horn is a pneumatic device that produces a loud noise for signaling, working by passing a stream of compressed air through a reed or diaphragm inside a horn, which vibrates to create sound waves that the horn then amplifies. Air horns are widely fitted to large buses, semi-trailer trucks, fire trucks and trains as vehicle warning devices, to some ambulances, and to ships as a signaling device. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/