Pierre Curie discovered that quartz crystals vibrate.

Best known for his research on radioactivity with his wife Marie, Pierre Curie (1859-1906) also played a pioneering role in the history of the quartz watch. Curie observed the phenomenon of piezoelectricity in 1880 while working with his brother, Jacques. They discovered that certain quartz crystals produced electricity when put under pressure. They later determined that the reverse was also true; when electricity is applied to the crystal, it deforms and vibrates.

These vibrations enable the quartz crystal to act as a very reliable timekeeper.

The quartz crystal in a modern timekeeper acts as an oscillator, replacing the balance wheel of the mechanical watch. It vibrates at a constant rate, measured in cycles per second. An electronic circuit counts these regular vibrations and translates them to time of day, date, or other time-related information.