The detent escapement was developed in the late 18th century during the marine-chronometer race that followed the British Longitude Act (1714). John Arnold (UK) developed the spring detent (1779); Thomas Earnshaw (UK) refined it (1781) into the form used in most 18th-19th century marine chronometers. The mechanism delivers impulse to the balance only on alternate beats and the release is via a tiny gold spring (the 'detent'), eliminating the sliding friction that the lever escapement creates during unlock-and-impulse.
Why it isn't in wristwatches: the detent is sensitive to shock (a sudden movement can mis-trigger the release) and position (the mechanism works best in a stationary horizontal pocket-watch position). Marine chronometers were carried in gimballed boxes specifically to keep them horizontal. A wristwatch experiences far worse position and shock conditions than a chronometer-box pocket-watch, so the detent's accuracy advantage disappears under real wrist conditions. Modern wristwatches with detent escapements (Urban Jürgensen, Vianney Halter Antiqua, Christophe Claret pieces) are connoisseur references rather than practical accuracy plays.
