By monitoring human behavior unobtrusively, mobile sensing technologies have the potential to improve our daily lives. Initial results from a field study demonstrate that such passive technologies can detect a complex psychological state in an uncontrolled, real-life environment. In the web extra at https://youtu.be/n8Ap3Z44ojQ, guest editor Katarzyna Wac interviews authors Adela Timmons and Theodora Chaspari, quality-of-life technology researchers at the University of Southern California.