This thing is quite amazing – it features a heart rate meter, x, y, z-axis motion sensitivity, temperture sensor, battery voltage and altitude (based on temperature, not a barometer) and has wifi, USB, connects to stuff and is fully programmable. Best of all, it only costs $49,-
This is the press blurb: TI revolutionizes design of wireless networking applications with eZ430-Chronos, world’s first customizable development environment in a sports watch – News Room – News Center.
You can find the development tool here
A wiki with loads of information here