A new app designed to track a person's mood throughout the day could turn your smartphone into a pocket therapist, researchers claim.
The free app takes advantage of the fact phones are increasingly capable of collecting information about where we are, how noisy our environment is, how much we are moving around and who we communicate with.
It will invisibly monitor data such as a user's calling and texting patterns to track their conversations and work out how they are feeling.
Using the phone's built-in global positioning system, accelerometer and microphone, it will develop a pattern of that person's habits, activities and routines.
The Emotion Sense programme, available for free on Android phones and developed by the University of Cambridge's Computer Laboratory, will work as the phone's owner goes about their normal life.
Dr Neal Lathia, who works on the project, said: "Behind the scenes, smartphones are constantly collecting data that can turn them into a key medical and psychological tool.
"Any smartphone now comes with numerous sensors that can tell you about aspects of your life, like how active you are, or how sociable you have been in the past 24 hours.
"In the long term, we hope to be able to extract that data so that, for example, it can be used for therapeutic purposes."
The app's designers hope they can collect a precise record of what drives people's emotional peaks, showing, for example, when they are likely to be at their most stressed.
It is part of a research project looking at how far smartphones can go in recording mood in the real world.
Eventually this could see phones being routinely used to monitor people's behaviour and change it for the better to improve health and well-being.
Cecilia Mascolo, a reader in mobile systems at the Cambridge Computer Lab, said: "Most people who see a therapist may only have an appointment once every fortnight.
"Many, however, keep their phones with them most of the time. In terms of sheer presence, mobiles can provide an ongoing link with a person."
Once the phone has collected information, the user is then asked to complete a brief survey to clarify their emotional state.
Throughout the day the app will pop up to ask how that person is feeling, rating their mood from positive to negative and registering how active they have been.
"Most other attempts at software like this are coarse-grained in terms of their view of what a feeling is," Jason Rentfrow, from Cambridge's department of psychology, said.
"Many just look at emotion in terms of feeling happy, sad, angry or neutral. The aim here is to use a more flexible approach, to collect data that shows how moods vary between people."