1. An optoelectronic sensor ( 10 ) for monitoring a working area ( 42 ), 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 , 40 a - 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 , 40 a - 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, characterized in that the illumination control ( 28 ) comprises a short range object detection unit ( 39 ) configured to test the provisional working area ( 40 , 40 a - c ) in a different way than the object detection unit ( 30 ) tests the working area ( 42 ).