A detection unit comprising detection means for detecting the occurrence of an event, processing means for controlling the operation of the detection unit, and communication means for transmitting and receiving activation signals for interacting with further detection units, wherein the processing means are designed for placing the detection unit into active mode upon receipt of an incoming activation signal, and wherein the processing means are further designed for transmitting, in the active mode, an outgoing activation signal to at least one of said further detection units upon detection of an event and placing the detection unit into passive mode.