Fitness trends and health-care problems are creating demand for tiny computers we won’t even notice we’re carrying.

What if your doctor had already received the information from a tiny device built into your cell phone, wallet, or undershirt? Sonny Vu, a cofounder of the medical-device company AgaMatrix, believes a device like this could fundamentally change health care.

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 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, and make it possible automatically provide medical services such as remote monitoring of patients or automatic detection of falls.