Robust, wide-area sensing of human environments has been a long-standing research goal. We present Sozu, a new low-cost sensing system that can detect a wide range of events wirelessly, through walls and without line of sight, at whole-building scale. To achieve this in a battery-free manner, Sozu tags convert energy from activities that they sense into RF broadcasts, acting like miniature self-powered radio stations. We describe the results from a series of iterative studies, culminating in a deployment study with 30 instrumented objects. Results show that Sozu is very accurate, with true positive event detection exceeding 99%, with almost no false positives. Beyond event detection, we show that Sozu can be extended to detect richer signals, such as the state, intensity, count, and rate of events.

Research Team: Yang Zhang, Yasha Iravantchi, Haojian Jin, Swarun Kumar, and Chris Harrison