Vehicle horn

A horn is a sound-making device that can be equipped to motor vehicles, buses, bicycles, trains, trams, trolley cars, streetcars, and other types of vehicles. The vehicle operator uses the horn to warn others of the vehicle's approach or presence, or to call attention to some hazard. Motor vehicles, ships, and trains are required by law in some countries to have horns. Bicycles like trams, trolley cars and streetcars in many areas are also legally required to have an audible warning device, but not universally, and not always a horn.