A sensor network comprising a first sensor (104) and a second sensor (101, 108), characterized in that: the first sensor (104) and the second sensor (101, 108) are configured to detect an event and to generate a message (M1, M2, M3) corresponding to the detected event; and wherein the sensor network is configured to provide an assessment of the message (M1) from the first sensor (104) based on the message (M2, M3) from the second sensor (101, 108).