Digital watch
From Futurepedia, the Back to the Future Wiki
A digital watch was a form of timepiece created in late 20th century. They consisted of liquid crystal displays and were equipped with an electronic beeping sound for an alarm.
Marty McFly's digital watch never seemed to have the correct time. Even though it had no moving parts and didn't "tick", Marty had a habit of looking at his watch, holding it to his ear and shaking it whenever Emmett Brown told him the correct time.
While in Lou's Cafe in 1955, Marty McFly's digital watch alarm sounded while he was making a phone call to Emmett Brown.
The LCD digital watch would not be invented until 1972, by the Swiss manufacturer, Longines, which introduced the watch in early 1973 [1].
