Presence detector for ceiling mounting indoors. The sensor module detects moving heat sources (e.g., people) within an adjustable detection range and activates a stair light timer. The sensor module needs to be completed with a compatible insert. It can be mounted in a standard 60mm flush-mounted box or in the surface-mounted housing available as an accessory. The sensor module features a light sensor with an adjustable brightness threshold, ensuring that the lighting only turns on below a certain brightness level. Thanks to the presence function, the sensor module can turn off the lighting even when a person is present if there is sufficient natural light. The switchable light control (only in combination with dimmable inserts) ensures nearly constant brightness in the room. The sensor module continuously measures the brightness in the room and adjusts it to a set target value.