The Watchismo blog has a mind-blowing history of early spy-cameras built into wrist-watches:
1960 Tessina Cameras featured the only subminiature watch that uses standard 35mm film but is the size of 16mm cameras. A rare version exisits for the wrist (above) and one with a Swiss watch attachment (below). Made up of 400 parts and built by Concava of Switzerland, the Tessina was also designed and patented by Dr. Rudolph Steineck.
See also:
Solid wood pocket-watch from 1900
Pictorial history of kids’ watches
History of armored military watches
History of slide-rule wristwatches
Early days of plastic watches
Mechanical “LED watch” from 1970
History of calculator watches
Steampunk watch
Watch guts of great beauty
All-plastic watch movement from the 70s
Awesome, impractical, expensive watch