You won't find this on ThinkGeek, I don't think.

[bktheirregular]

Reading marthawells' article on world-building problems, specifically mentioning timekeeping, reminded me of something I'd seen a while back:

The First Atomic Clock Wristwatch

Not, mind you, a watch that adjusts itself from a radio signal transmitted from NIST. No, this is a fully self-contained cesium clock, worn on the wrist.

(While you're there, check out "Project GREAT", an interesting proof of the variability of time.)