The Serendipity system senses a social environment and cues informal interactions between nearby users who don?t know each other, but probably should. The system uses Bluetooth hardware addresses to detect and identify proximate people and matches them from a database of user profiles. We show how inferred information from the mobile phone can augment existing profiles, and we present a novel architecture for instigating face-to-face interaction designed to meet varying levels of privacy requirements. Finally, we discuss features that respond to experience in an on-going user study involving 100 subjects.