Fairchild digital quartz wristwatch with LED display, 1970-1979.
© Science Museum / Science & Society Picture Library
Watches with light-emitting diode (LED) displays were the first digital watches. LED displays require relatively large amounts of power to operate, so the display is inactive until a button is presed to reveal the time. LED display watches were superceded by ones with liquid crystal displays (LCDs), which use far les power and can therefore show the time constantly.