Wireless sensor networks have emerged as a technology that are being quickly adopted due to their flexibility and use in a variety of environments. However, they consist of small, inexpensive devices or nodes that have severe constraints such as limited bandwidth, limited processing power, short battery life, small storage capability and are physically prone to external threats. Sensor Network are emerging as a new tool for important application in diverse fields like military surveillance, habitat monitoring, weather, home electrical appliances and others. These sensor nodes have some constraints due to their limited energy, storage capacity and computing power. The energy efficiency is an important issue in WSN.