In this paper, we propose a novel IEEE 802.15.4 media access control (MAC) power management scheme that achieves the user specified reliability with minimal power consumption at the node. Also, we develop an accurate mathematical model to analyze the effects of constrained on-node memory for sensed data storage on the MAC layer performance. We use three-dimensional Markov chain and M/G/1/K queue to model the IEEE 802.15.4 MAC and on-node packet queue, respectively. By formulating the precise packet service time, the reliability, packet queue overflow losses, delay, and power consumption of the node are analyzed. When compared with simulations and the real-time test bed, the proposed model achieves an accuracy of 97% and 94%, respectively. Also, the performance analysis shows that the proposed power management scheme provides energy savings of up to 74.82%. © 2005-2012 IEEE.