In May 2005 Nokia Sensor application (www.nokia.com/sensor) was launched, allowing mobile phone users to create digital identity expressions, seen by other users within Bluetooth range. This paper describes the design and mass-scale longitudinal field trial of a precursor prototype called DigiDress. 618 participants voluntarily used the application for an average of 25 days. The identity expressions created were both serious and playful, revealing and nonrevealing. Factors influencing the identity expression included strategies for personal impression management, privacy concerns, and social feedback. The application was used with both acquainted and unacquainted people, and viewing the identity expression of people nearby was one major motivation for continued use. Direct communication features such as Bluetooth messages were not commonly adopted. DigiDress acted as a facilitator for ‘real’ social interaction between previously unacquainted users. Privacy concerns and their allevi...