Emergency Vehicle Sirens

Drivers of emergency vehicles in the United Kingdom at least, generally using at least two types of sirens (sometimes more) they seem to alternate as they drive. What is the reason for the siren and not everyone has a special significance or purpose?

There are 3 or 4 different tones and volume settings on the unity of the siren.

Some drivers tend to "settle" on the sirens, it was found that a change in pitch or a type of sound re-reporting. A change also gives an indication of the direction of the siren is coming.

It has nothing to do with the type of emergency.

distinguish if its the police or simply an ambulance

I do not know exactly, but I know now, here in Texas, they put "Screamers" on some. I guess maybe in the bubble that is your car, you can not hear certain sounds. - I can hear the howler before I heard the sirens.

"Isitme" hit the nail on the head.

I used to drive a vehicle of the army bomb disposal and when they are called to serve in finding that the change in the "Music" got more reaction than keeping the same noise is constant.
The siren is an electronic box and you can move from one key to another, it also has a public address system where you can say for certain vehicles to be off the road, going forward, etc.

Where I work (and this is the same on most emergency vehicles), we have two main colors on the sirens:

Wailers and yelpers.

The Wailers be a long tone you hear when driving over a certain distance and yelpers are used when approaching a red traffic light or an area of heavy traffic or other dangers, it 's acts in the shortest tone you hear.

The purpose of the different tone to alert people of your presence in the area, they are more likely to hear if the siren tone suddenly changes.

It does not always work but usually some people still do not hear or see us coming!

They only have a siren that can be of type adjusted.The sirens depend entirely on Whatever model of service decide to buy and there is no national standard.

Here's why I think they do:

Probably for the safety of other drivers. If you live in a center of large cities like London, New York, Toronto, you'll probably always hearing sirens in the distance. A driver can hear the siren, but not realize that the emergency vehicle is behind them or about to run a red light. If the substitute that will keep the driver alert.