This paper presents a novel architecture designed for low power consumption, in which low computational complexity and reliability have also been important design constraints. It is suitable for sensor-actuator systems, is based on IEEE 802.15.4 and constitutes a more lightweight alternative than Zigbee. We provide a vision of how we have solved some problems that are out of the scope of IEEE 802.15.4 like addressing scheme, topology control, multi-hop synchronization, tasks scheduling, application data model, and other points related to software and hardware considered to extend the battery life. We have designed a centralized method for scheduling the beacon transmission time. Unlike the distributed one used by Zigbee, our method avoids beacon overlapping in any case and does not require the publication of information in the beacon payload. The proposed addressing scheme also does not require the publication of the depth of coordinators. Both methods allow us to implement efficient algorithms, reduce the memory used to store the network tables, and shorten the beacon payload, what entails a significant energy saving. These solutions together with others presented in this paper allow us to reach a battery life longer than 31 months for sensors and 42 months for actuators.