The use of wireless sensor networks in structural health monitoring can significantly increase safety and reduce manufacturing and maintenance costs. Wireless sensor networks typically use low footprint smart active sensor nodes that are permanently mounted on the structure, have the processing power to detect changes in the structure indicating impending hazards and communicate wirelessly with other sensor nodes or base stations when anomalies are detected. This paper presents the development and implementation of sensor node hardware and software for passive and active sensing of elastic guided waves. A distributed control algorithm is presented for controlling a wireless sensor network from a base station. The overall system is applied using a network of lead zirconate titante sensors mounted on a thin aluminum plate. Initial results of damage detection using the system demonstrate the feasibility of the approach followed.