Various Types of Sirens as an Alarm Device

1. Various Types of Sirens as an Alarm Device Why is it that sirens in emergency vehicles have a wide range of sounds emitting from them? The basic explanation is well brought out by Dylan in Chicago. He said,“Over the years I’ve noticed a variety of siren sounds for emergency vehicles. Is it true siren sounds have to be changed periodically, particularly in urban areas, to prevent drivers from getting used to a particular sound and not paying attention?”

2. This might or might not be true but the fact is that there is a large variety of sounds emitting from the siren box in emergency vehicles. There are two very common in the USA alone. The first is the wail, the familiar and traditional siren with a rise and fall in pitch which in the olden days varied with the speed of the car. The second is the yelp whose pitch alternates very rapidly, almost representing today’s fast-paced life.

3. There is also the European-style two-tone high-low siren which is ideal for capturing the attention of the people and traffic along the way and is now often interspersed with whoops and other noises. The phaser siren is another option and penetrates into interiors the best. This is why it is the most used siren at intersections. Finally, there is the “braying” air-horn which is actually the modern electronic version of the traditional air-horn.

4. In the strictest sense, it is not a siren but is equally effective in getting people out of the way or signaling the arrival of an emergency vehicle. The siren use policy is not standardized across the USA and varies from State to State. California and Hawaii have restricted the use of sirens to the wail and the yelp pitch only. Hawaii has further fine-tuned the siren policy whereby the wail is limited in police vehicles to the usual emergencies and the yelp for traffic offenders to signal them to pull over. Emergency drivers though generally cycle through the different siren types to quickly capture attention.

5. There is another critical reason for having multiple siren sounds on different emergency vehicles such as police cars, fire-trucks, and ambulances. If all emergency vehicles had the same type of sirens, they would not be able to differentiate between each other’s sirens when speeding to the same location. It is known as the wash-out effect and can lead to crashes.

6. How loud are sounds from a siren box? Sound is measured in decibels and doubles every 10dB. Therefore 60dB is twice as loud as 50dB. The sound of a police siren is usually 110dB, 128 times louder than 40dB, the sound level in a quiet library.