One of the most challenging issues in the design of system for Wireless Sensor Networks (WSN) is to keep the energy consumption of the sensor nodes as low as possible. Many localization systems require that the nodes keep the transceiver active during a long time consuming energy. In this work we propose a scheme to reduce the energy consumption of the mobile nodes that need to know their positions. Our strategy consists of decreasing the idle listening and an optimized allocation of the localization tasks on the nodes. Thus, the nodes that are externally powered calculate the position for the resource-constrained nodes. The scheme is based on a low-power IEEE 802.15.4 non-beacon enabled network.