The electric opener

The electric overhead garage door opener was invented by C.G. Johnson in 1926 in Hartford City, Indiana. Electric Garage Door openers did not become popular until Era Meter Company of Chicago offered one after World War II where the overhead garage door could be opened via a key pad located on a post at the end of the driveway or a switch inside the garage.
Contrary to popular belief, the electric opener does not provide the actual lifting power to open and close a heavy garage door. Instead, most of the actual lifting power comes from the counterbalance springs attached to the door. These springs are under tension to lift the garage door via steel counterbalance cables. The electric opener only controls how far the door opens and closes, as well as the force the garage door exerts. In most cases, the garage door opener also holds the door closed in place of a lock.

Information compliments of Wikipedia