A sensor network is a network of many smart devices, called nodes, which are spatially distributed in order to perform an application-oriented global task. The field of wireless sensing holds the potential to greatly change the way people live. Pushing these devices to smaller, cheaper and more functional implementations greatly increases the scope of their application. WSNs will proliferate in a vast range of potential applications including academic, industrial, agricultural, domestic and military. In typical sensor network applications, the sensors are left unattended for a long period of time once they have been deployed.