Key winding was the norm from the earliest spring-driven watches into the second half of the nineteenth century: a detachable key engaged a square on the barrel arbor to wind, and a second square, often accessed through the dial or a hinged cuvette, to set the hands.
The disadvantages were practical rather than mechanical. A lost key stopped the watch. A worn square rounded off. Winding through the back risked driving dust and moisture past a cover intended to exclude both, and setting the hands meant opening the case at the front, exposing the movement.
Keyless mechanisms replaced the key with a crown at the pendant, coupled to the movement through a stem. Winding turns a clutch wheel engaging the barrel train; pulling the crown, or in earlier designs pressing a separate button, shifts a sliding pinion or rocking bar so the same crown instead turns the motion work to set the hands.
Several distinct systems reached the market from the 1840s onward, associated with names including Adrien Philippe, Jean-Adrien Philippe's contemporaries at Patek Philippe, and independent inventors on both sides of the Atlantic; negative-set (button-operated) and later pendant/lever-set systems coexisted for decades, and American railroad practice favoured lever setting specifically because it could not be disturbed accidentally in a pocket.
Attribution of 'the' inventor of keyless winding is contested in the literature: multiple mechanisms were patented independently in the same general period, and popular accounts that credit a single individual with the whole concept oversimplify a genuinely parallel development. Treat any single-inventor claim as a simplification unless a specific patent and date are cited.
For dating a movement, the winding and setting system is strong circumstantial evidence: pure key-wind movements cluster before roughly the 1860s–1880s depending on market, keyless negative-set and lever-set systems dominate later production, and the exact form of the keyless works (position of the setting lever, style of clutch) can sometimes narrow a movement to a specific maker or ébauche supplier.