Fire Siren

A fire siren is another name for an air raid siren or outdoor warning siren used to summon volunteer firefighters for emergencies. While fire sirens were the primary means of alerting firefighters for many years, more modern means of notification have now been implemented to replace the fire siren. As there can be problems with modern communications, many fire departments (typically in smaller communities) still sound the siren as a backup or auxiliary to these devices (for example, pagers and radios). Many fire sirens also pull double duty as tornado or civil defense sirens, alerting an entire community of impending danger. Most fire sirens are either mounted on the roof of a fire station, or on a pole next to the fire station. Fire sirens can also be mounted near government buildings, on top of tall structures such as water towers, as well as in systems; where several sirens are sporadically placed around a town for better sound coverage. Most fire sirens are single tone and mechanically driven by electric motors with a rotor attached to the shaft. Some newer sirens are electronically driven by speakers, though not as common. The most common types of sirens include the Federal Signal Model 5, Model 2, STH10, STL-10, SD-10, and the Sterling (now Sentry) siren Model M. Fire sirens are often called "fire whistles", "fire alarms", "fire horns" even though the nomenclature is incorrect. Although there is is no standard signaling of fire sirens, some utilize codes to inform firefighters to the location of the fire. Civil defense sirens pulling double duty as a fire siren often can produce an alternating "hi-lo" signal (similar to a British police car) as the fire signal, or a slow wail (typically 3x) as to not confuse the public with the standard civil defense signals of alert (steady tone) and attack (fast wavering tone).

By Wikipedia