An air horn is an air-filled device that creates a deafening noise. These devices or horns are typically used for signalling purposes (mostly for long-distance signals where the standard horn cannot be heard). These horns consist of a source that creates compressed air that passes into a horn through a diaphragm or reed. The stream of air in this device causes the reed to vibrate and create sound waves. The horn then amplifies thunderous sounds. These types of horns are typically installed in heavy vehicles like buses, fire trucks, ambulances, trains, trailer trucks etc.