The paper introduces a new secure power aware many-to-many routing protocol for wireless sensor and actuator networks. Actuators register for sensing data and sensor nodes send data directly to actuators using the proposed protocol. The protocol has two versions. The first version is designed for networks where every node transmits at the same power level. The second version is for the case where nodes can individually adjust the transmission power according to the channel conditions and communications distance. The protocol increases energy efficiency and prolongs network life-time while still keeps the communications secure. Copyright © 2012 John Wiley & Sons, Ltd.