The Watch That Traded Its Mainspring for a Battery

In January 1957, the Hamilton Watch Company of Lancaster, Pennsylvania, put the first electric wristwatch on sale: the Hamilton 500 movement.

It still had a swinging balance wheel, like any mechanical watch, but no mainspring. Instead, a coil of wire rode on the balance itself, two small magnets sat fixed beneath it, and the balance acted as its own switch: once each swing, a contact briefly closed, a button-cell battery energized the coil, and the repelling magnets gave the balance a tiny push onward, much like timing a push on a swing. It beat 18,000 times an hour.

The case was as striking as the movement: an asymmetric shield shape called the Ventura, styled by the car designer Richard Arbib. Elvis Presley wore one in the film Blue Hawaii (1961) and gave others as gifts.

The contacts, it turned out, were the weak point: they wore down and needed regular service, and an improved movement, the 505, arrived in 1961. Even so, the idea itself had already proven the point: a watch could run on a battery.