The sound emitted by a tornado siren differs by location. Sirens in Ohio sound a three-minute steady tone. Sirens in Kentucky sound like a louder version of the siren from an emergency vehicle and are designed to be heard from at least ? mile away.
Some areas use different siren sounds for tornado warnings and tornado watches. The sirens are intended for people outdoors and may not always be audible indoors. Most areas test their sirens regularly, sometimes at a lower volume than when used for emergencies. State and county emergency departments often offer an audio sample of the tornado siren on their websites for residents.
Most jurisdictions use mechanical sirens that force air through rotors to produce the pitch and intensity of the siren. Modern electronic sirens use sound generators and amplification systems capable of producing various sounds for different types of emergencies, as well as vocal instructions.
The tornado siren sound in Aurora, Colorado is typical of most sirens and sounds for three minutes.to indicate that the National Weather Service has issued a tornado warning, and that a possible tornado has been sighted within city limits. This siren is used for a variety of other emergency situations and alerts residents to immediately head indoors and seek additional information.
Illinois distinguishes tornado warning sirens from other alerts, such as those indicating enemy attacks, by using a single tone for tornado warnings sirens and a tone that rises and falls in pitch for attack warnings.