Recent advancements in wireless communications enabled the development of small and cheap nodes capable of sensing, communication and computation. These nodes in a network co-ordinate to perform distributed sensing of environmental phenomenon in various fields such as health, military, home. Research on energy sensitive routing in static WSN has led to the development of many routing protocols that ensure max life time of network. In this paper we explore ERFLA which will effectively use the limited resources of a sensor node to improve the network lifetime. We explore and evaluate this algorithm on a simple WSN analytically and experimentally. Our evaluation indicates that our algorithm has shown 30%–40% improvement in the network lifetime over comparable protocols like leveling, PASCAL [4].We also present a theoretical model of cognitive sensor network which uses few specialized nodes which have capabilities of spectrum sensing.