The winding key axle of a fairly conventional clock is fitted with a set of connected glass tubes and vials filled with alcohol. A heating element below the lower-most vial causes the liquid to vaporize and move up to the opposing upper vial. Now separated from the heat source, the alcohol cools again to form a liquid. The orientation of the heavy liquid filled vials on top causes the winding axle to rotate. Perhaps a bit of a fire hazard -- heat, glass, alcohol, bare wires and 220 volts...Yikes! Not exactly "set it and forget it" to my way of thinking, but ingenious nonetheless.
From The Watchismo Times and found via BoingBoing.net.