A communications system comprises a primary wireless network and at least one secondary wireless networks, the primary and secondary wireless networks differing in at least one characteristic, at least one sensor unit comprising a means for sensing a parameter and a node of that secondary network adapted to transmit data relating to the parameter via that secondary network, at least one local data gathering point associated with the at least one secondary wireless network, incorporating a node of that secondary wireless network, a node of the primary network, and a control unit adapted to receive data signals from the at least one sensor unit via the secondary network, construct an outgoing data signal incorporating information from the received data signal, and transmit the outgoing data signal via the primary network, the primary wireless network being a multipoint radio network. The primary wireless network is optimized for relatively long distance communications, of the order of 10 kin, and the secondary network or networks are optimized for relatively short distance communications of the order of 100 m, the radio power of each network being different and appropriate for each transmission distance required. The nodes of the primary network may contain GPS receivers, to synchronize the sensors with which the nodes communicate, and aid routing performance of the primary wireless meshing network.