How do sound sensors work?

A popular sound sensor is called a microphone. There are various designs and technology used, but the principle is the same.

You need a diaphragm. This is any (generally thin and light) material that is suspended in air. The pressure waves in air, that we call sound, make the diaphragm move.

In a dynamic type microphone, a coil of fine wire is also attached to the diaphragm and is surrounded by a magnet.

As the coil moves, so it generates small amounts of electricity, which can then be amplified and manipulated how you want.