A verification device to detect possible faults in occupancy sensors of a connected lighting system , the connected lighting system comprising multiple luminaires and multiple occupancy sensors (161- 164), the multiple luminaires being partitioned into control zones which are controlled in dependency on one or more corresponding occupancy sensors (161- 164), the connected lighting system being organized according to a hierarchical structure wherein the multiple occupancy sensors are at a first hierarchical level, the control zones are at a second hierarchical level, the multiple occupancy sensors at the first hierarchical level corresponding to control zones at the second hierarchical level, the control zones being partitioned into sets which are at the third hierarchical level, the connected lighting system being connected to a database and is arranged to store sensor data obtained from the multiple occupancy sensors of the multiple luminaires, the verification device comprising: - an input interface arranged to connect to a database and obtain the sensor data obtained from the multiple occupancy sensors, - an aggregation unit arranged to compute occupancy values which are indicative of average occupancy over a specified time period at different hierarchical levels by applying a statistical measure, an occupancy value at the first hierarchical level indicating an occupancy value of an occupancy sensor, an occupancy value at the second hierarchical level 215, 281) indicating of an occupancy value of a control zone, and an occupancy value at a third hierarchical level indicating an occupancy value of a set of control zones, and - a processing unit arranged to compare an occupancy value at a lower hierarchical level with a corresponding occupancy value at a higher hierarchical level, finding deviations between said occupancy value at a lower hierarchical level and said corresponding occupancy value at a higher hierarchical that are more than a threshold and that indicate a possible fault in the connected lighting system and producing a signal to communicate the possible fault. - an input interface arranged to connect to a database and obtain the sensor data obtained from the multiple occupancy sensors, - an aggregation unit arranged to compute occupancy values which are indicative of average occupancy over a specified time period at different hierarchical levels by applying a statistical measure, an occupancy value at the first hierarchical level indicating an occupancy value of an occupancy sensor, an occupancy value at the second hierarchical level 215, 281) indicating of an occupancy value of a control zone, and an occupancy value at a third hierarchical level indicating an occupancy value of a set of control zones, and - a processing unit arranged to compare an occupancy value at a lower hierarchical level with a corresponding occupancy value at a higher hierarchical level, finding deviations between said occupancy value at a lower hierarchical level and said corresponding occupancy value at a higher hierarchical that are more than a threshold and that indicate a possible fault in the connected lighting system and producing a signal to communicate the possible fault. <EOS>