Air horn

The air horn is a device designed to create an extremely loud noise. It is usually composed of a pressurized air source coupled to a horn through a valve which allows the device to be turned on and off. Air horns have been installed on large semi-trailer trucks, fire trucks, and some ambulances for many years.

Emergency Vehicles

Many fire trucks, ambulances, and other large emergency vehicles operate air horns as a means of warning vehicles to clear the right-of-way. These may include traditional "truck" style air horns, or stuttertone air horns, which produce an easily recognizable tone. Most, if not all, US firetrucks have stuttertone air horns installed.

There are also electronic varieties of "air horns" for emergency vehicles, which produce a similar easily-recognizable sound. These are typically integrated into the same system as the vehicle's electronic siren, and sound through the same speakers. There are also air-horn only systems available, which some states allow for use by volunteers in their personal vehicles.

Trucks

More recently, some individuals are adding truck air horns (and even louder train horns that sound a minor-seventh chord rather than the major chord of truck horns) to their personal autos as a hobby or addition to the culture of bigness exemplifed by SUVs.

It should be noted that the use of a train whistle in an automobile could cause an accident.

The reverse has been noted, in which:

Original diesel locomotives did not have whistles, but were equipped with truck horns. After the accident, the bus driver exclaimed that he had heard the train, but had thought that it was a truck. link

Portable air horns are also readily available, utilizing a small aerosol spray can as the air source. These are often present at sporting events such football and soccer, and at other outdoor events..

Popular Culture

It is a common game among school children (especially on field trips, which are more likely to involve travel on a major highway) riding a school bus to pump their fists, imitating the motion of a truck driver operating an air horn, in order to request that passing drivers sound their horns. If the driver obliges, the passengers will generally respond with great amusement, sometimes despite chastisement. Such chastisement is more likely to come from teachers or fellow students, as bus drivers are generally used to distractions.

Sports

The airhorn has a big presence in ice hockey, especially in the NHL. There are normally two horns; a small high one that announces the end of the period, and a much louder lower one that is sounded when the home team scores and/or wins the hockey game.

Music

The airhorn is a popular sample in reggaeton music.