via – Sundial and Stardial Pendants | ThinkGeek.
It may not be as accurate as modern technology but it is interesting to use historical technology and… you wouldn’t have to buy batteries (or recycle batteries).
I can’t wear a battery operated watch. For some reason the batteries die within a week or two. I was looking for a mechanical watch. So far I haven’t found just the right one. This would be interesting but… the reviews say it isn’t very accurate. Still tempting to try it though.