Automatic Watch
An automatic watch is a mechanical watch that winds itself from the movement of your wrist. A rotor inside swings as you move and tightens the mainspring, so it needs no battery. Worn every day it keeps running; left off for a few days it stops and has to be rewound.
At the heart of an automatic watch sits the rotor, a half-moon weight that spins with the movement of your wrist. As it turns it winds the mainspring, and that stored energy drives the watch. Fully wound, most hold around 40 hours of power reserve, so a watch taken off on Friday may still be running on Monday. It is less precise than quartz, and a few seconds of drift a day is perfectly normal. Expect a service every few years. The Seiko 5 and Orient Mako are affordable, classic examples.