A sensor network is a series of stand-alone distributed sensor nodes that communicate information to a gateway for retrieval. Sensor networks are used to monitor a wide range of conditions over a greater area than is possible with a single sensor package. There is no typical setup for a sensor network; networks can range from just a few nodes to hundreds, collecting any kind of imaginable data. Sensor networks are commonly used for industrial, security, and scientific applications and can be set up as passive data collectors or active controllers. Sensor networks are not made upon any single technology; they are made by integrating a variety of other technologies.