Check out the Goodwatch from Travis Goodspeed https://github.com/travisgoodspeed/goodwatch
It is a"replacement circuit board for the Casio 3208 module, used in the Casio CA-53W and CA-506 calculator watches" and very neighborly.
http://josh.gourneau.com I am a belt buckle engineer http://tnbelt.com
I am also an enthusiast of Python, Django, Linux, and mobile devices.