The last time your doctor asked how much you exercise, did you tell the truth? Do you even really know the truth—not just how many visits to the gym you've made this month, but how many hours you sit or how many calories you burn in a day?

What if your doctor had already received the information from a tiny device built into your cell phone, wallet, or undershirt? Sonny Vu believes a device like this could fundamentally change health care. "You can't just lie to your doctor—it's all there, recorded," he says. "You cut right to the chase rather than having to tease out all that information."

Vu is an entrepreneur who thinks a lot about how a well-designed mobile device can affect health. As a cofounder of the medical-device company AgaMatrix, he created the first FDA-approved glucose sensor that plugs into an iPhone; it hit Apple stores this month under the brand name iBGStar.

Now Vu is taking his ideas a step further, betting that the next phase for mobile computing is on our bodies. He's heading a new company called Misfit Wearables, which is developing health monitoring devices that he says will fit unobtrusively into the clothing and objects we use every day.