We're starting to see a bunch of ear-worn devices whose main purpose is to gather biometrics rather than just provide music. One of the more advanced is Bodytrak, from the British company Inova. The device, which incorporates sensors from Valencell, measures heart rate, oxygen consumption, location, speed, and body temperature. It also allows two-way communication and the ability to hear what's going on around you.
What's particularly interesting about Bodytrak is that it is chasing after markets that provide hostile environments: First response, defense, health and safety, and sports. An accurate report of a first responder's biometrics and location can be a matter of life or death -- as are high-quality communication and long battery life. The Bodytrak is comparatively large, fitting mostly over the ear rather than strictly within it. But there's a lot of technology in there, and it's a device made for work, not for play.
Pricing is not yet set, and availability is expected in the latter part of the year.