A network formed from large numbers of small sensors deployed in the field that use wireless to communicate. The sensors usually configure their communication network on the fly by identifying their nearest neighbours. Typically, the sensors are designed to measure some feature of interest in the environment, such as temperature, or to sense the presence of a pollutant. The key issue is designing communication protocols that maximize the battery lifetime of the sensors, while also ensuring that all interesting measurements get reported. See also ad hoc networks.