Casio developed a radio-controlled wrist watch only half as thick as those on the market.

Radio-controlled wristwatches receive a standard-time radio signal and adjust themselves accordingly.
Casio's new design uses miniaturized components, including a smaller antenna and battery, and packages the signal reception chip and peripheral circuit elements into a 70 percent smaller footprint so that all components can be mounted on a single side of the board. The result is a watch that fits in a 42-millimeter-diameter case, similar in size to competing products, but is only 6-7mm thick.
More details at Asia Times Online.

Casio plans to release the watch before the end of the year in japan and will price it at about 30,000 yen (US$275).

See also:
I4U votes Casio Exilim EX-S20 Best Small Digital Camera
2 Mega Pixel Camera Phone - Casio A5403CA