Can your cell phone tell if you’re happy or overworked?

Researchers at the Massachusetts Institute of Technology think it can do that and more–separate the rich from the poor, the sick from the healthy, even the outgoing from the introverted. Sandy Pentland, director of MIT’s Human Dynamics Research program, has focused his work on that unlikely task: using gadgets as simple as a cell phone to better understand the quirks and patterns of human behavior.

Pentland’s experiments began with what he calls a “sociometer,” a simple badge-like device that hangs from a subject’s neck and records his or her movements, tone of voice, and location. With just those signals collected from large groups of subjects, Pentland says he was able to perform a kind of data analysis he calls “reality mining,” finding patterns that reveal a surprising range of information–from how a population breaks down into groups, to which groups are most social and productive, to the personality traits of single individuals, all based on measuring tone of voice and body language.

In his most recent experiments, however, the sociometer hasn’t been necessary. Instead, Pentland has tracked his subjects through their cell phones, which are carried by around four out of five Americans. Pentland spoke with Forbes.com about the benefits his tracking experiments could offer to society, the privacy problems they pose and how he hopes to strike a balance between the two.

Forbes.com: What is “reality mining?”

Sandy Pentland: Reality mining is about using sensors to understand human beings. The sensors could be security cameras, they could be devices that you wear on yourself, they could be cell phones. The point is it’s about people. Data mining is about finding patterns in digital stuff. I’m more interested specifically in finding patterns in humans. I’m taking data mining out into the real world.

What kind of reality-mining experiments have you actually performed?

We developed this thing called a sociometer, a little badge that you wear around your neck that records your body language, your motion and your tone of voice–the tone, not the words. It gives us a nice little package for reality mining.

We’ve done all sorts of interesting things with this. Just listening to peoples’ tones of voice and how they move, we can measure interest level and attention, factors that account for 40% of the variation in the outcomes of things like salary negotiation, dating scenarios, closing a sale, pitching a business plan.