A method of operating a monitoring sensor comprising a light transmitter; a light receiver; and a deflection unit is described, with the method comprising the steps: a) detecting a respective detected signal that comprises a time curve of a reception signal received for an angle of rotation; b) determining the number of reception light pulses in the detected signal; c) generating a detection signal that comprises information on the determined position of an object, wherein checks are made in accordance with first, second and third test conditions, and with the first test condition being checked in a first test step, and one of the second and third test conditions being checked in possibly performed second and/or third test steps respectively.