Wireless Sensor Network (WSN) technology has been getting a lot of attention in recent years due to its low-cost, portability, easy deployment, self-organisation, and reconfigurability. Two main challenges faced by designers are availability and power/energy management for WSN. This paper presents a design for a wireless sensor node, which provides automated reconfiguration for both availability and energy-efficient use. This design introduces an original device named Power and Availability Manager (PAM) combined with a FPGA. The first one is considered as the intelligent part for the best use of energy and fault-tolerance, while the other enhances the availability in case of hardware failure for a node. Simulation model of these solutions together is based on General Stochastic Petri Net (GSPN). The results indicate a gain of availability from 9% to 31% for sensor node over twelve years, from 9% to 46% for sensor cluster over eighteen years, from 11% to 45% for whole network over fifty years. Our approach also results in significant energy-saving : up to 61% by using DPM policy, and up to 62.5% by using DPM and DVFS policies over seven days. These results allow us to evaluate and to show a design of WSN node for increased availability as well as energy-saving by using our approach