How does a siren work?

Siren

A siren is a kind of whistle which makes a loud noise as air is blown through holes in a spinning cylinder or disk.  It is a wailing noise

When a fire truck roars through the streets, its loud siren warms people to get out of the way.  An ordinary air siren has two cylinders, one inside the other.  The cylinder contain a number of holes.

When the fireman presses the button, an electric motor spins the inner cylinder and air is pushed through the holes.

When the holes in the inner cylinder are lined up with the holes in the outer cylinder, puffs of air escape and cause vibrations.  When the vibrating air (sound waves) reach our ears,  you hear the familiar ooooooOOOOOOEEEEEEeeeeee noise of the siren.

The faster the inner cylinder spins, the greater number of puffs of air, and the louder the siren.  A newer kind of siren makes its wailing sound electronically.  It does not have a moving parts like the older types. – Dick Rogers

Can dogs hear better than people?

Dogs can hear many sounds that our ears cannot hear.  If you have a pet dog, then you know what keen ears dogs have.  A dog will bark at approaching footsteps long before they are heard by his master.

It’s easy enough to hear noises.  You can hear with noises, loud noises, and in-between noises. All sounds are produced in the same way.  Every kind of sound begins with the vibration of something.

Tikoy

When a bell is rung, the bell shimmers and shakes.  We say, that it “vibrates.”  When a lion roars, the voice cords in the lion’s throat vibrate.

These vibrations disturb the air and cause sound waves that travel outward like ripples in a pond, and when they reach your ear they make part of your ear vibrate, too.  That’s when you hear the sound.

But we cannot hear all the sounds around us.  Our ears can only hear certain sound vibrations. Some animals, like the dog, can hear sound vibrations that humans cannot.  

The “silent” dog whistle makes a sound vibration so high and so shrill that you can’t hear it – dogs can!  A cat can hear even higher sounds.  And the bat can hear the highest sounds of all. – Dick Rogers