Sensor (3) and method for the detection of the movement of an encoder to be monitored with at least two sensor elements (6, 7), which are arranged in a way offset relative to each other in the direction of movement of the encoder, and with a processing circuit (10, 14, 15), which converts the element output signals (S1, S2) at the outlets of the sensor element (6, 7) to a sensor output signal (S5) that describes the movement of the encoder, with the processing circuit (10, 14, 15) including a test circuit (14), which monitors the element output signals (S1, S2) at least indirectly and disables or corrects the sensor output signal (S5) when errors of the element output signals (6, 7) are detected.