Adopting techniques to increase operation time of battery-powered sensor nodes in wireless networks is necessary when implementing practical monitoring applications intended to run over extended periods of time. Energy harvesting; DC-DC converter techniques; and features of modern microcontrollers like extreme lower consumption, Sleep and Idle states, can contribute to improve the performance of network nodes. Designers can also use the possibilities offered by special protocols for wireless sensor networks, routing algorithms, and data aggregation plus collection strategies. Issues related to the process of design and implementation of an energy-efficient sensor node operating under IEEE 802.15.4-compliant MiWi protocol from Microchip® Technology are presented. Operating tests were conducted in different hardware/firmware scenarios in order to verify the changes in node’s performance depending on the adopted configuration.