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The heart of any watch is a regulator that runs at a constant rate. In a quartz watch, this is an oscillator circuit that runs a 32768Hz. In a real (ie, mechanical) watch, it is a balance wheel and hairspring with a constant resonant frequency of a few Hertz.
Steam engines, however, can also be made to run at constant speed, my means of a Watt centrifugal governor. The governor consists of two heavy balls on hinged arms, affixed to the output shaft of the steam engine. As the shaft speed rises, the balls are thrown outward by centripugal force, and this in turn closes a valve, reducing the steam supply and slowing the engine. If the shaft slows, the reverse occurs.
With this in mind, it is astonishing that nobody has produced a steam wristwatch until now. The governor will have to rely on springs (rather than gravity) for the centripugal force to act against, but will otherwise remain pretty much the same. Furnishing a miniature wrist- mounted firebox, boiler and piston arrangement are problems too trivial to dwell upon. A simple asbestos pad will ensure the continued comfort of the wearer.-- MaxwellBuchanan, Feb 10 2016 Wankel watch Wankel_20Watch [MaxwellBuchanan, Feb 10 2016] It's about time - this is a hot idea.-- normzone, Feb 10 2016 I have trouble with the firebox. Instead this watch should run with some liquid having a boiling point near human skin temperature. I think now of those birds with the glass belly full of methyelne choride one might use to peck an ALARM OFF button if you were working at the Springfield nuclear reactor. Phase changes of volatile liquids - all that. But you might need something more volatile yet to power it with body heat. Ether? Bromine? Bromine definitely is cooler looking.
For such a watch, a condenser circuit with fins to shed heat could be dolled up in a fashionable fashion.-- bungston, Feb 10 2016 //some liquid having a boiling point near human skin temperature
Hmm, a bit like my room temperature steam engine, which has been so pooh-poohed here enough already..just think twice..-- not_morrison_rm, Feb 11 2016 random, halfbakery