The app, called Student Life, has been developed by researched from Dartmouth College, a private university in the United States. Student Life uses the smartphone sensors to track movement and location, and at the same time records the number of text messages and phone calls. In addition, this app activates regular microphone which is able to recognize calls. Student Life processes the information on physical activity, communication patterns, sleep patterns, visiting sites and conversation that students have without using their smartphone. Student Life students showed a then-week run on their smartphone. Many changes in these patterns and activities correlate with changes of mood, as appears from the questionnaires completed by the students. This app was particularly able to recognize stress, depression and loneliness. They are looking into expanding their research to include alerts to remind the app users to change their state of mind.
Referenced from: http://www.technologyreview.com/news/530876/this-phone-app-knows-if-youre-depressed/