A distance-measuring optoelectronic sensor for the monitoring of a working zone is provided which is located within a detection zone of the sensor and at a first distance from the sensor, wherein the sensor has a lighting unit having a light source to illuminate the working zone at least partly as well as an object detection unit by means of which unauthorized objects in the working zone can be detected. In this respect, an illumination control is designed, in a switching-on phase, first to activate the lighting unit with a lower power so that a provisional working zone at a second distance from the sensor less than the first distance is illuminated with at most a preset maximum power; to check by means of the object detection unit whether an unauthorized object intrusion is taking place into the provisional working zone; and if no unauthorized object intrusion is recognized, to activate the lighting unit at a higher power so that the working zone is illuminated with at most the preset maximum power.