Car alarm Car alarm A car alarm is an electronic device installed in a vehicle in an attempt to discourage theft of the vehicle itself, its contents, or both. Car alarms work by emitting high-volume sound (often a vehicle-mounted siren, klaxon, pre-recorded verbal warning, the vehicle's own horn, or a combination of these) when the conditions necessary for triggering it are met. Such alarms may also cause the vehicle's headlights to flash, may notify the car's owner of the incident via a paging system, and may interrupt one or more electrical circuits necessary for the car to start. Although inexpensive to acquire
Train horn steam whistle. This is why most train horns have a unique sound, different from that of road going trucks, although many switch engines, which didn't see road service (service on the main lines), retained the deeper truck-like horns. Strict regulations specific to each country specify how loud horns must be, and how far in advance of grade crossings and other locations locomotive engineers are required to sound their horns to give adequate time to clear the tracks. Standard signals consisting of different sequences of horn blasts must be given in different circumstances. Due to the encroachment of development, some suburban