A method of detecting a source using: a plurality of nodes (5a-d, 11-25), each node including a sensor capable of collecting data, wherein the sensors are radiation or chemical sensors, and a transmitter configured to transmit at least sensor data collected by the sensor and location data representing at least the location of the node; a network capable of allowing transmission of data between and among the plurality of nodes and between the plurality of nodes and at least one computer; and a first computer having an input configured to receive data transmitted by nodes through the network, a memory configured to collect data transmitted by the nodes through the network, a processor configured to combine sensor and location data and compare the combined data to a predetermined detection criterion to determine whether a source is detected, and an output; the method comprising: collecting, in the first computer, location data transmitted through the network from each node to the first computer, the data being associated with a predetermined time; for each node, associating the node at the predetermined time with at least one of a plurality of node groups based at least in part on at least one of (a) a velocity of the node, and (b) a measure of traffic on the network; for each node group, determining whether a source has been detected by the node group by combining, in the first computer, sensor data and location data collected from the nodes in the group and comparing, in the first computer, the combined sensor data and location data to at least one predetermined detection criterion; and signaling, with the output, at least whether a source has been detected. a plurality of nodes (5a-d, 11-25), each node including a sensor capable of collecting data, wherein the sensors are radiation or chemical sensors, and a transmitter configured to transmit at least sensor data collected by the sensor and location data representing at least the location of the node; a network capable of allowing transmission of data between and among the plurality of nodes and between the plurality of nodes and at least one computer; and a first computer having an input configured to receive data transmitted by nodes through the network, a memory configured to collect data transmitted by the nodes through the network, a processor configured to combine sensor and location data and compare the combined data to a predetermined detection criterion to determine whether a source is detected, and an output; the method comprising: collecting, in the first computer, location data transmitted through the network from each node to the first computer, the data being associated with a predetermined time; for each node, associating the node at the predetermined time with at least one of a plurality of node groups based at least in part on at least one of (a) a velocity of the node, and (b) a measure of traffic on the network; for each node group, determining whether a source has been detected by the node group by combining, in the first computer, sensor data and location data collected from the nodes in the group and comparing, in the first computer, the combined sensor data and location data to at least one predetermined detection criterion; and signaling, with the output, at least whether a source has been detected. collecting, in the first computer, location data transmitted through the network from each node to the first computer, the data being associated with a predetermined time; for each node, associating the node at the predetermined time with at least one of a plurality of node groups based at least in part on at least one of (a) a velocity of the node, and (b) a measure of traffic on the network; for each node group, determining whether a source has been detected by the node group by combining, in the first computer, sensor data and location data collected from the nodes in the group and comparing, in the first computer, the combined sensor data and location data to at least one predetermined detection criterion; and signaling, with the output, at least whether a source has been detected.