Sirens

A siren is a sound producing device. The sound produced by a siren is usually interrupted at regular intervals. The interruption of the sound in a siren is produced by a rotating disk, which is usually perforated. A hooter is a sound producing device or a specialised vehicle horn. This device is used in vehicles to make a loud warning sound. 
A typical siren consists of an air source, a rotor, and ports in a stator for the air to escape. The Rotor contains many ports that interrupt the flow of air at the required frequency. The siren contains a compressor to supply the air and the rotor is driven by a motor. There is another type of siren called the electromechanical siren that uses two electric motors. One of the electric motors is used to supply the air. This air then, produces the acoustic signal. The other electric motor is used to rotate the rotor. Another type of siren is the indoor siren. These sirens are used as alarm systems in houses and offices. The indoor alarm system alerts the owner of a burglar has broke into the home or office. The sirens used in the indoor alarm system are generally of 15 to 20 watts.
Hooters are mounted on the vehicles and have a switch button near the steering wheel or handle. Hooters are powered by the batteries of the vehicle. The different types of warning lights are industrial warning lights, lightning warning lights, aviation warning lights, obstruction warning lights, Rail and road warning lights.