Abstract: Once a fire door has been installed, the door will typically require regular inspection to ensure that the fire door is still able to operate as intended. An issue typically seen with fire doors is related to the gaps between the door and the frame that being too large. The present disclosure provides a self-testing fire door system 100 comprising a first distance sensor 140 arranged to measure a first distance between a fire door 110 and a door frame 120. The first distance sensor 140 comprises a first sensor member 141 arranged on the door frame 120 and a second sensor member 142 arranged on the fire door 110 adjacent to the first sensor member 141 when the fire door 110 is in a closed position. The system 100 further includes a processor configured to measure, via the first distance sensor 140, a distance between the fire door 110 and the frame 120 and output the first distance.