An optoelectronic sensor (10) for monitoring a working area (42) is provided, the working area (42) being located within a detection area (20) of the sensor (10) and in a first distance from the sensor (10), wherein the sensor (10) comprises an illumination unit (22) with a light source (24) for at least partially illuminating the working area (42), and an object detection unit (30) for detecting forbidden objects in the working area (42), wherein an illumination control (28) of the illumination unit (22) is configured to, during a startup period, initially activate the illumination unit (28) with a lower power such that a provisional working area (40, 40a-c) in a second distance from the sensor (10) less than the first distance is illuminated at most with a predetermined maximum light output; test whether there is a forbidden object intrusion into the provisional working area (40, 40a-c); and if no forbidden object intrusion is detected, activate the illumination unit (28) with a higher power such that the working area (42) is illuminated at most with the predetermined maximum light output. The illumination control (28) comprises a short range object detection unit (39) configured to test the provisional working area (40, 40a-c) in a different way than the object detection unit (30) tests the working area (42).