The self-winding pocket watch was invented by Abraham-Louis Perrelet in 1777, decades before Abraham-Louis Breguet's own "perpétuelle" of 1780. Perrelet's design used a pivoting weight inside the pocket watch that oscillated as the wearer walked, winding the mainspring via a ratchet. The walking motion was never perfectly suited to a pocket watch (a watch lying still in a waistcoat does not wind), so automatic pocket watches remained a curiosity for 150 years.
The wristwatch changed the equation. A watch strapped to a wrist experiences hundreds of small motions every hour. In 1922, English watchmaker John Harwood patented the first practical self-winding wristwatch, using a pivoting weight that bumped against two buffer springs at the ends of its travel (a "bumper" automatic). Harwood watches sold around 30,000 units through the late 1920s before his company went bankrupt in the 1929 crash.
The breakthrough came in 1931 with Rolex's Perpetual rotor, invented by Emile Borer: a full 360-degree rotating weight on a central pivot. Every wrist motion, large or small, contributed to winding in either direction. Combined with the Oyster case, the Perpetual rotor made the Rolex Oyster Perpetual the blueprint for every modern automatic wristwatch. The central 360-degree rotor is now standard across the industry.
The micro-rotor, a smaller rotor integrated flat into the movement plate, was developed by Buren in 1955 and serialised by Patek Philippe from 1960 (Cal. 240). Micro-rotors allow thinner movements at the cost of slightly slower winding efficiency. Other variants include the peripheral rotor (Audemars Piguet Cal. 2870, 1986; modern Breguet and Carl F. Bucherer implementations), where the rotor runs on ball bearings around the outside of the movement, and the bidirectional vs unidirectional winding choice: most watches wind in both rotor directions for efficiency; some (IWC Pellaton) use a one-directional system with a reversing wheel.
