Abstract : Energy-efficiency is generally regarded as one of the fundamental challenges for wireless sensor networks and the radio part is a major contributor to overall energy consumption of a sensor node. A Radio Triggered Sensor MAC (RTM) protocol was introduced in the literature, which could harvest the overall energy consumption in WSNs. In this article, we propose, design and develop hardware which we refer as Passive Radio Sensor (PRS) and use is to study the RTM protocol in WSNs. A general radio transceiver, typically used in WSN, consumes a significant amount of energy when periodically listening to data messages. Our proposed transceiver hardware, PRS, powered by the incoming radio signals themselves and hence significantly reduces node energy consumption that is wasted in radio communications. The PRS circuit is independent of any other components on the node. Keywords: ZigBee, Radio-Triggering.