A wireless sensor network (WSN) (sometimes called a wireless sensor and actuator network [https://scholar.google.co.uk/scholar?oi=bibs&cluster=11960246589498210561&btnI=1&hl=en] (WSAN)) are spatially distributed autonomous sensors to monitor physical or environmental conditions, such as temperature, sound, pressure, etc. and to cooperatively pass their data through the network to a main location. The more modern networks are bi-directional, also enabling control of sensor activity. The development of wireless sensor networks was motivated by military applications such as battlefield surveillance; today such networks are used in many industrial and consumer applications, such as industrial process monitoring and control, machine health monitoring, and so on.