Compared to police lights, that have undergone tremendous changes over the years, especially after the arrival of LED lights on the scene, a police siren has undergone limited changes. The pneumatic sirens that were used in the beginning in emergency vehicles were replaced later by electronic sirens which used amplifiers with better effect, and also are more energy efficient. Pneumatic siren is still used in rare instances along with an electronic siren.

The main difference in a police siren these days is that there is software that can produce as many types of sounds as the user chooses and can record human voice and also reproduce it with modifications. But such sounds are, however, rarely used. The main sound patterns that a police siren uses are wail, yelp, air horn, phaser, manual, hi-lo or two tone sound, and a similar tri-tone sound.

A wail, perhaps the sound produced most frequently by a police siren, is a dragging, keening sound, which sounds more or less like a wail itself. The yelp is the faster barky sound that a siren emits. The tone and sound intensity of a police siren is decided by the operator. Most operators choose to have the wail when the vehicle is moving straight through the same lane but choose to have the jumpy yelp when the vehicle reaches traffic junctions.

Though the sound of an air horn is used comparatively less in a police siren, many larger emergency vehicles like ambulances and fire trucks use an air horn for the extreme loudness of the sound and the resultant better warning ability. There are stutter-tone air horns that are a modification on the conventional one and produce a distinctive sound. Some air horns are integrated into the electronic siren system while some function independently of it. Volunteer firefighters and rescue workers are allowed the use of air horn in some states.

Other police siren sounds like phaser, manual etc. are also available in most sirens. Operators often switch from one sound to another or change volume to make the sound more effective. Most operators change sound patterns and sound intensities based on the noise level of the street, amount of traffic on the street, and the emergency of the situation. The sound controls will have separate switches for various sounds and override options and combination options that can be easily programmed. The control panel of a police siren will have full nighttime visibility to aid operation in darkness.

The sound of a police siren is not good for anybody's ears, and is extra harmful for operators who remain continuously exposed to it. Operators are always advised to use hearing protection. The sound of sirens even pierces into the homes at the dead of the night. It is in the best interests of everyone that a police siren is operated only when it is absolutely necessary. When the road is not crowded, and the emergency vehicle can move at the chosen speed without warning other vehicles, it is best not to use it.

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