Wireless Sensor Networks (WSNs), sometimes called sensor networks and wireless actuators (WSANs), are autonomously spatially distributed sensors for monitoring physical or environmental conditions, such as temperature, sound, pressure, etc. locations. The most modern networks are bidirectional, also allowing the control of the activity of the sensor. The development of wireless sensor networks was motivated by military applications such as battlefield surveillance; today these networks are used in many industrial and consumer applications, such as monitoring and control of industrial processes, monitoring the health of machines, etc.
The WSN is constructed of "nodes" - from a few to several hundreds or even thousands, where each node is connected to one (or sometimes several) sensors. Each node in the sensor network typically has several parts: a radio transceiver with an internal antenna or a connection to an external antenna, a microcontroller, an electronic circuit for interfacing with the sensors and a power source, usually a battery or an integrated form of energy collection. A sensor node can range in size from that of a shoebox to the size of a grain of dust, although functional "motes" of genuine microscopic dimensions have not yet been created. The cost of sensor nodes is similarly variable, ranging from a few to hundreds of dollars, depending on the complexity of the individual sensor nodes. The size and cost limitations of sensor nodes result in constraints corresponding to resources such as power, memory, computational speed, and communications bandwidth. The WSN topology can range from a single star network to an advanced multi-hop wireless mesh network. The propagation technique between network jumps can be routing or flooding.