WASHINGTON, USA: A new smart phone senses your depression and nudges you to go out with friends, a study reveals.

It's the future of therapy at a new Northwestern University Feinberg School of Medicine centre where scientists are inventing web-based, mobile and virtual technologies to treat depression and other mood disorders.

The phone and similar projects bypass traditional weekly therapy sessions for novel approaches that provide immediate support and access to a much larger population, a university statement said.

"We're inventing new ways of technology that can help people with mental health problems," said psychologist David Mohr and professor of preventive medicine at Northwestern's Feinberg School.

"The potential to reduce or even prevent depression is enormous," said Mohr.

"These new approaches could offer fundamentally new treatment options to people who are unable to access traditional services or who are uncomfortable with standard psychotherapy," said Mohr.

"They also can be offered at significantly lower costs, which makes them more viable in an era of limited resources," added Mohr.

The goal is for the Feinberg centre to become a national resource, offering a library of intervention technologies that will be available to other researchers.

Also in the works are a virtual human therapist which will work with teens to prevent depression; a medicine bottle that reminds you to take antidepressant medication and tells your doctor if the dosage needs adjusting; and a web-based social network to help cancer survivors relieve sadness and stress.