The basic work of sensor system is to monitor required event and communicate it to base station and hence to the end user. Wireless Sensor Networks were first developed to use at places where wired sensors networks cannot reach for example: latest Tsunami in Japan, where environment is polluted with nuclear radiations. In order to get latest happenings in such an environment wireless sensors can be deployed randomly and information can be fetched through them by the user sitting at a very far and safe distance. As the cost of installation and maintenance of wired sensor networks is quite high as compared to wireless sensor networks, wireless sensor networks prove themselves as an attractive alternative as compared to wired sensor networks. With the passage of time, sensor nodes find their way to household and day to day work also. Now days, they are used as health monitoring systems, agriculture, structural engineering, real time monitoring in civil engineering, human tracking etc. As in case of any network, security becomes an important issue in wireless sensor networks too.