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Are You Being Heard? Sirens and Air Horns Can Make a Difference

NCJ Number
Law Enforcement Technology Volume: 29 Issue: 7 Dated: July 2002 Pages: 88-93
David Olsen
Date Published
July 2002
6 pages
This article discusses the types of police sirens currently available.
There are two basic types of sirens: electro-mechanical and electronic. Electro-mechanical sirens have been generically referred to as growlers, grinders, wind-up sirens, and coaster sirens. This siren uses a motor to spin a rotor inside a stator and is a centrifugal air pump. It creates a sound as the airflow is forced to bounce back out the front of the siren. The emergency vehicle driver controls the running of the siren motor by using a momentary foot switch that turns on the motor as the switch is depressed. This manual function was said to be too hard to operate and has since lost favor in law enforcement. Electronic siren controllers have one box performing several functions, reducing the amount of space needed in the console of the patrol car. The controller can provide switches to control the warning lights, alley/scene lighting, shotgun lock release, generate audible warning signal, and the public address/radio rebroadcast capability. It simulates the wail sound of the electro-mechanical siren and offers other sounds such as yelp, hi-lo, air horn, and others. Electronic sirens have lower amp draw than the electro-mechanical siren, and are less expensive, lighter in weight, and provide multiple sounds. Department considerations in getting the most of a siren include verifying proper wiring, where the speaker is mounted, and how it is oriented in relation to the vehicle. The speaker needs to point straight ahead and be perpendicular to the pavement. The optimal location is out in front of the vehicle. If State law governing emergency vehicle sirens requires compliance with the Society of Automotive Engineers (SAE), some siren tones used by themselves may be illegal. If a siren cannot be heard over the din of traffic, it is recommended that a set of air horns be added. Research has shown that the typical electronic siren is inadequate as an audible warning device. It is particularly bad for determination of source direction. The use of Localizer siren sounds from Sound-Alert Ltd., currently marketed in the United Kingdom and Canada, showed significant improvement over electronic sirens. The Localizer siren sounds are full spectrum or “broadband” noise.