Siren used on emergency vehicles such as ambulances, police cars, and fire trucks. Siren is a device that makes a loud noise. Civil defense sirens permanently installed and used to warn of natural disasters or terrorist attacks. The majority of fire sirens mounted on the roof of a fire station or on a pole adjacent to the fire station. Fire alarms also installed on or near government buildings, as well as on tall structures such as water towers. The majority of fire sirens are single-tone and mechanically powered by electric motors with a rotor attached to the shaft. More recent sirens use electronically powered speakers. Newer sirens powered by electronic speakers.