Since sensor nodes normally have limited resources in terms of energy, bandwidth and computation capability, efficiency is a key design goal in sensor network research. As one of techniques to achieve efficiency, data aggregation has been extensively investigated in recent literature. Previous research on data aggregation has demonstrated its effectiveness in reducing traffic, easing congestion and decreasing the energy consumption. However few are actually designed for a real-world application and implemented in a running system. This paper describes our design and implementation of a physical tracking system, using an aggressive data aggregation architecture as one of building blocks. This architecture can be generally applied to other sensor systems, where communication efficiency is a paramount concern and networking resources are limited.