Abstract: A display device (10) comprises an input/output channel for receiving data from a source and at least one sensor (36) operable to obtain sensor data on the display device (10). Selected ones of the or each sensor (36) are arranged to operate in response to the display device (10) receiving a request in the data from the source via the input/output channel, and the display device (10) is arranged to output the sensor data obtained by the or each sensor (36) to the source via the input/output channel. A system for monitoring at least one property of such a display device (10) comprises a monitoring unit (32) which is connectable to the one or more sensors (36) via the input/output channel to provide the request and receive the sensor data from the one or more sensors (36). The system can thereby monitor at least one property of the display device (10).