— In this paper, we propose a new dual radio medium access control (MAC) protocol for wireless sensor networks. Our MAC protocol design combines the advantages of low and high frequency bands in different modes of MAC operations in order to result in energy efficiency. Our prototype also supports spectrum agility, which is becoming important due to ever crowding wireless spectrum. We present the detailed design rationale and individual micro-level experimental performance evaluation of the MAC protocol on our prototype sensor node platform. We also make comprehensive empirical performance comparisons with the widely used B-MAC protocol and show the performance gains that our MAC protocol is able to achieve under various traffic loads and duty cycles.