In this paper we propose an analytical model to detect and remove malicious nodes while taking into account MAC IEEE 802.15.4 beacon-enabled technology. The proposed solution called muDog enables to monitor nodes activities with a minimal energy consumption in order to detect the suspicious behavior particularly the non-cooperative nodes in the routing process. Moreover, we analyze the cost of the monitoring mechanism in terms of energy consumption and the quality of detection by the evaluation of the monitor's observation. The impact of nodes density, packets' size, network traffic load: saturated/unsaturated cases and distance between monitor and monitored nodes are taken into account in our evaluation. The obtained results illustrate that muDog is more efficient than Watchdog whatever the parameter is.