Last month, attendees at the World Economic Forum in Davos, Switzerland, pulled out their smart phones. Each attendee watched as the gadget displayed an analysis of his or her mental state—relative to others in the room—gleaned from data gathered by the phone itself.

A special program, which they'd agreed to install earlier in the conference, mined accelerometer data to tell when the phone had been moved, counted time spent on e-mail, and noted how long they'd kept the phone unlocked, and where and when they connected to Wi-Fi. "We could point out 'you're not very active right now,' or 'you're not paying attention to this lecture,' or 'you're jet lagged,'" Alex "Sandy" Pentland, the professor of media arts and sciences at MIT who developed the program, told the audience.