| Compared to police lights, that have undergone | | | | of the sound and the resultant better warning |
| tremendous changes over the years, especially | | | | ability. There are stutter-tone air horns that are a |
| after the arrival of LED lights on the scene, a | | | | modification on the conventional one and produce |
| police siren has undergone limited changes. The | | | | a distinctive sound. Some air horns are integrated |
| pneumatic sirens that were used in the beginning | | | | into the electronic siren system while some |
| in emergency vehicles were replaced later by | | | | function independently of it. Volunteer firefighters |
| electronic sirens which used amplifiers with better | | | | and rescue workers are allowed the use of air |
| effect, and also are more energy efficient. | | | | horn in some states. |
| Pneumatic siren is still used in rare instances along | | | | Other police siren sounds like phaser, manual etc. |
| with an electronic siren. | | | | are also available in most sirens. Operators often |
| The main difference in a police siren these days is | | | | switch from one sound to another or change |
| that there is software that can produce as many | | | | volume to make the sound more effective. Most |
| types of sounds as the user chooses and can | | | | operators change sound patterns and sound |
| record human voice and also reproduce it with | | | | intensities based on the noise level of the street, |
| modifications. But such sounds are, however, | | | | amount of traffic on the street, and the |
| rarely used. The main sound patterns that a police | | | | emergency of the situation. The sound controls |
| siren uses are wail, yelp, air horn, phaser, manual, | | | | will have separate switches for various sounds |
| hi-lo or two tone sound, and a similar tri-tone | | | | and override options and combination options that |
| sound. | | | | can be easily programmed. The control panel of a |
| A wail, perhaps the sound produced most | | | | police siren will have full nighttime visibility to aid |
| frequently by a police siren, is a dragging, keening | | | | operation in darkness. |
| sound, which sounds more or less like a wail itself. | | | | The sound of a police siren is not good for |
| The yelp is the faster barky sound that a siren | | | | anybody's ears, and is extra harmful for |
| emits. The tone and sound intensity of a police | | | | operators who remain continuously exposed to it. |
| siren is decided by the operator. Most operators | | | | Operators are always advised to use hearing |
| choose to have the wail when the vehicle is | | | | protection. The sound of sirens even pierces into |
| moving straight through the same lane but choose | | | | the homes at the dead of the night. It is in the |
| to have the jumpy yelp when the vehicle reaches | | | | best interests of everyone that a police siren is |
| traffic junctions. | | | | operated only when it is absolutely necessary. |
| Though the sound of an air horn is used | | | | When the road is not crowded, and the |
| comparatively less in a police siren, many larger | | | | emergency vehicle can move at the chosen |
| emergency vehicles like ambulances and fire | | | | speed without warning other vehicles, it is best |
| trucks use an air horn for the extreme loudness | | | | not to use it. |
