I got interested in some of the activities of the Atomic Devices and Instrumentation Group at NIST, as they have performed some pretty impressive miniaturizations on certain atomic instruments they've been researching, including, evidently, working chip scale atomic clocks. So I sent an email to John Kitching, who, I believe, heads up that research group asking about new developments and whether the miniaturization work might at some point get us to a chip scale atomic wristwatch. Here is his reply for anyone who's interested:
"Thanks for your inquiry. It is very unlikely that the chip-scale atomic technology will reach a point where it could be used in a wristwatch in the near future. The problem is not so much with the size of the instrument but with the power requirements. The existing generation of chip-scale clocks run on ~ 100 mW of power. This would have to be reduced to below 100 microW to make it possible to run it for any length of time on a wristwatch battery. I'm not quite sure why one would want to put one in a wristwatch anyway, other than for marketing...
John's last sentence would seem to suggest that he hasn't heard of the uber-geeks on this forum....