Wearable devices to monitor bodily functions now constitute a multi-billion-dollar industry. Fitbit, Jawbone Up and other gadgets keep track of your blood pressure, sleep patterns, calories burned and how many steps you take in a day. The idea is to apply technology to human biology in order to develop healthier habits, but the value of self-awareness has limits. All that data can be overwhelming — and compromise privacy. Will tracking and collecting so much personal information give new power to insurance companies and government agencies?