In this paper, we describe the GroupMedia system, which uses wireless wearable computers to measure audio features, headmovement, and galvanic skin response (GSR) for dyads and groups of interacting people. These group sensor measurements are then used to build a real-time group interest index. The group interest index can be used to control group displays, annotate the group discussion for later retrieval, and even to modulate and guide the group discussion itself. We explore three different situations where this system has been introduced, and report experimental results. Categories and Subject Descriptors J.4 [Computer Applications]: Social and Behavioral Science – Psychology, Sociology General Terms Measurement, Experimentation and Human Factors. Keywords Human behavior, interest, speech features, galvanic skin response, head nodding, prosody, influence model