Supporting a surveillance of positions of devices

Each of a plurality of transmitters, which are distributed at fixed locations of a site, regularly transmits radio signals. A mesh node performs measurements on radio signals transmitted by at least one transmitter and transmits messages including results of the measurements. The mesh node belongs to a plurality of mesh nodes, each configured to monitor at least one environmental parameter at the site. A gateway node receives messages transmitted by the mesh node directly and/or via at least one other mesh node of the plurality of mesh nodes, wherein each of the plurality of mesh nodes is configured to receive messages from other mesh nodes of the plurality of mesh nodes and to forward received messages. The gateway node transmits received messages to a server that is configured to monitor mesh nodes at the site based on results of measurements.