Vehicle horn

another ripped content from wikipedia for my pleasure:

A vehicle horn is a sound-making device used to warn others of the approach of the vehicle or of its presence. Automobiles, trucks, ships, and trains are all required by law to have horns. Bicycles are also legally required to have an audible warning device in many jurisdictions, but not universally, and not always a horn.

[edit]BicycleHorn types

Classic bicycle horns usually consist of a single horn operating at a single resonance frequency, with a reed made of steel located in the throat of the horn, and supplied with air by a rubber squeeze bulb. Other variations include battery operated horns, and small air horns powered by a small can of compressed gas.

[edit]Automobile

Horn switch is generally situated at center of the steering wheel.

Oliver Lucas of Birmingham, England developed a standard electric car horn in 1910. Automobile horns are usually electric, driven by a flat circular steel diaphragm that has an electromagnet acting upon it and is attached to a contactor that repeatedly interrupts the current to the electromagnet. This arrangement works like a buzzer or electric bell and is commonly known as "sounding" or "honking" one's horn. There is usually a screw to adjust the distance/tension of the electrical contacts for best operation. A spiral exponential horn shape (sometimes called the "snail") is cast into the body of the horn, to better match the acoustical impedance of the diaphragm with open air, and thus more effectively transfer the sound energy. Sound levels are approximately 107-109 decibels, and current draw 5-6 amperes.