A covering for an opening in a building and a sensor assembly, wherein the covering comprises a panel and a frame member, and wherein the sensor assembly comprises a sensor module, the sensor module housing two inductive sensors (521, 522) and a transmitter, wherein one of the panel or frame member comprises a locking member and the sensor module is positioned on the other one of the panel or frame member, wherein the panel is moveable relative to the frame member between an open position and a closed position, and the panel is moveable to an intermediate position between the open position and the closed position, wherein the locking member is moveable to a first locked position when the panel is in the closed position to lock the panel in the closed position, and the locking member is moveable to a second locked position when the panel is in the intermediate position to lock the panel in the intermediate position, and wherein the sensor module is configured to sense the position of the locking member and, when the position of the locking member is sensed to be in the first locked position, the transmitter is configured to transmit a first signal indicating that the locking member is sensed to be in the first locked position, and when the position of the locking member is sensed to be in the second locked position, the transmitter is configured to transmit a second signal indicating that the locking member is sensed to be in the second locked position, characterised in that the sensor module is attached to the panel or frame member via a mount that is fixed to the panel or the frame member, wherein the sensor module comprises formations which interlock with the mount to hold the module in place upon the panel or frame member, and the one of the panel or frame member comprising the locking member further comprises a metallic member that is coupled to the movement of the locking member, and wherein the inductive sensors (521, 522) are configured to sense the proximity of the metallic member and to provide signals indicative of the proximity of the metallic member, and wherein the sensor assembly is configured to determine whether the panel is locked in the closed position or locked in the intermediate position by comparing the signals provided by each of the two sensors (521, 522) to reference values. wherein the covering comprises a panel and a frame member, and wherein the sensor assembly comprises a sensor module, the sensor module housing two inductive sensors (521, 522) and a transmitter, wherein one of the panel or frame member comprises a locking member and the sensor module is positioned on the other one of the panel or frame member, wherein the panel is moveable relative to the frame member between an open position and a closed position, and the panel is moveable to an intermediate position between the open position and the closed position, wherein the locking member is moveable to a first locked position when the panel is in the closed position to lock the panel in the closed position, and the locking member is moveable to a second locked position when the panel is in the intermediate position to lock the panel in the intermediate position, and wherein the sensor module is configured to sense the position of the locking member and, when the position of the locking member is sensed to be in the first locked position, the transmitter is configured to transmit a first signal indicating that the locking member is sensed to be in the first locked position, and when the position of the locking member is sensed to be in the second locked position, the transmitter is configured to transmit a second signal indicating that the locking member is sensed to be in the second locked position, characterised in that the sensor module is attached to the panel or frame member via a mount that is fixed to the panel or the frame member, wherein the sensor module comprises formations which interlock with the mount to hold the module in place upon the panel or frame member, and the one of the panel or frame member comprising the locking member further comprises a metallic member that is coupled to the movement of the locking member, and wherein the inductive sensors (521, 522) are configured to sense the proximity of the metallic member and to provide signals indicative of the proximity of the metallic member, and wherein the sensor assembly is configured to determine whether the panel is locked in the closed position or locked in the intermediate position by comparing the signals provided by each of the two sensors (521, 522) to reference values.