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ZigBee/IEEE 802.15.4 beacon-enabled mode allows low duty-cycle operation with high energy saving in the wireless sensor network. However, low duty cycles introduce higher end-to-end delay in event propagation and generally lower reactivity of the network with respect to the actual sensing. In target tracking systems, both qualities should be satisfied, namely, low energy consumption while no target is being tracked and low end-to-end delay in target tracking mode. Hence, we need to define a trade-off between the energy consumption and the end-to-end delay. In this paper, we propose a dynamic dual-rate beacon scheduling method with two rate switching schemes modifying ZigBee/IEEE 802.15.4 to enhance its real-time property but still maintain the advantage of low energy consumption. We evaluate our scheme through a simulation using the OPNET simulator. The results show that our scheme exhibits low energy consumption while presenting reduced end-to-end delay, outperforming usual single rate working modes.