Can a smart phone tell if you're depressed?

The app’s developer, San Francisco-based Ginger.io Inc., compared data from Ms. Flowers and nearly 200 other women against their answers to a weekly survey used to diagnose depression. The company says it found that behavioral patterns like decreased mobility on weekends and longer phone calls were associated with poor mood in surveys.

“It’s very creepy to think someone can tell your mood” based on smartphone data, says Ms. Flowers, who gave birth to twins last year. But “I felt like this was something that was going to help me while I was in a vulnerable place.”

The Ginger.io app is one of a new generation of health-surveillance technologies that doctors, hospitals and health insurers are starting to use. Where fitness trackers like FitBit record jogging distance and calories burned, newer apps and other tools measure text-message volume, vocal tone and other behaviors to peer into patients’ psychological well-being, which doctors say can have a high correlation with physical health. Health insurer Aetna Inc., for instance, says it uses voice-analysis software on some telephone calls to get people who receive short-term disability benefits back to work sooner.