The Nurse in Your Pocket

In 2009, researchers at the Massachusetts Institute of Technology gave a dorm full of students smartphones and tracked where they went, who they called and texted, and at what times they communicated. The researchers found that the data pouring out of the phones could reliably tell when a student was ill: Those stricken with the flu moved around much less, and those who were depressed had fewer calls and interactions with others.

Anmol Madan, the PhD student who led the study, concluded that the findings might be useful outside of dorms. There are now more than 60 million smartphones in the U.S., and they’re “incredibly powerful diaries of a person’s life,” he says. So in November 2010, Madan and his classmate Karan Singh, both 29, started Ginger.io to mine those diaries and provide the kind of detailed, persistent health monitoring that doctors and researchers have only dreamed of. “There hasn’t been large-scale, real-world data about how people behave” before now, he says.