Wireless sensor network
A wireless sensor network (WSN) is a network made of numerous small independent sensor nodes. The sensor nodes, typically the size of a 35 mm film canister, are self-contained units consisting of a battery, radio, sensors, and a minimal amount of on-board computing power. The nodes self-organize their networks, rather than having a pre-programmed network topology. Because of the limited electrical power available, nodes are built with power conservation in mind, and generally spend large amounts of time in a low-power "sleep" mode.
The University of California, Berkeley is a major center of research and development into wireless sensor networks, and has used them to study microclimate variations in individual redwood trees.