How do the sirens on police cas, fire engines, and ambulences work?

Answer 1

The old style sirens, the kind that had a rotor turning inside of it, and it sat either on a fender, or the roof, were different than the electronic type.
That old style had a housing with thin slots cut into the body of the housing. (The round part you could see!)
Inside the housing was an axle, upon which was a round casting, with regularly spaced high and low areas. An electric motor turned the later ones, but the old ones were turned by a crank.
The motion of turning the inner part past the slots in the outer casting is what made the sound. Faster revolutions made the sound go higher, slower revs made the sound go lower, causing the familiar siren noise we hear. It was the air passing thru the slots that made the noise! And don't poke yer finger into those slots!! It'll slice yer finger just like the slicer at the butcher shop!
On the other hand, the newer electronic sirens are mainly a recording played thru the sound system, not unlike music from a tape or CD. All the fireman or policeman has to do is turn on the player, then push the button that says:"SIREN", and it will make the siren sound! Some have to be pressed and not pressed, but the newer ones wail just like the older style! They even have a WAIL setting, where the siren will go up and down without anybody pressing a button to make it do that!

Answer 2

Years ago, they used rotating vanes that spun at different speeds inside a finned structure. The vanes moving by the fins at different speeds made the classic wailing noise.

Today, almost all sirens are electronically synthesized and played back through powerful loudspeakers. The same speakers can be used for a megaphone, where the police officer or fire fighter can tell someone to pull over or move back. Electronic systems can make a wide variety of sounds, which makes them preferable to the old mechanical sirens.

Answer 3

They have a little man in the boot who makes all the sounds.