Piezoelectricity is a phenomenon that allows certain materials to create electricity when vibrated and to vibrate when energized.

This phenomenon exists on a material used in watchmaking. It is quartz. When we put it under tension it starts to vibrate and we can use it as a resonator in an electronic watch.

Conversely, if you vibrate a quartz, it creates electricity. This is how, for example, a gas boiler can be lit by pressing a button. The button makes a quartz vibrate which creates a spark and lights the gas.