A group of patent applications filed by Motorola [NYSE: MOT] suggest that the company is toying with the idea of building Bluetooth headphones that incorporate biomentric monitors, measuring things like heart rate and temperature. According to the patent's schematics, the headset would be controlled by touch-sensitive buttons linked to the ROKR S9 handset, which would then relay the data to a server for storage (and presumably, later access).
Most biometric measurement devices come in the form of the wristwatch-and-chest-strap combo, and can measure and record similar vital signs for later download and analysis. By including that kind of functionality in a pair of Bluetooth headphones, Motorola could conceivably make a device that not only serves as phone and music player, but also as workout companion -- a pretty attractive package for the fitness set. That said, there aren't too many mobile phones that can handle the rigors (read: copious sweat, abuse and weather) of exercise, so there's no telling if this idea is plausible or not, whether it is approved its patent or denied it.