Quartz is used in watches as it acts as a piezoelectric oscillator. As a potential difference is applied across quartz, stress is generated across the perpendicular faces of the quartz crystal. It is known as reverse piezoelectric effect. The word piezo in Greek means pressure and, therefore, piezoelectricity means pressure electricity. It takes place in some crystals like quartz which lack certain symmetrical properties. A mechanical stress produces an electric polarisation and, reciprocally, an applied field produces a mechanical strain. So, this oscillator keeps watches ticking.