A sensor system for detecting motion in a predefined direction of motion (30) of an infrared light source (29) has at least one pair of infrared light sensors (4, 5; 36, 37), which are arranged side by side with respect to the direction of motion (30) and, thus, define a sensor coverage zone (17) determined by the distance between distal ends (16) (with respect to the direction of motion) of the infrared light sensors. During exposure to the infrared light source, the sensors provide electrical signals, the charge signs of which are opposite each other, for detecting the motion of the infrared light source (29). The sensor system (1) has a window (7) positioned between the infrared light source (29) and the sensors such that the infrared light of the infrared light source (29) radiates onto the sensors. The sensors are arranged behind the window and are adjusted relative to the width (41) of the window to extend in the direction of motion such that, beyond a predetermined limit distance (20) away from the window, each of the sensors has a full illumination zone (22, 23), which defines the locations from which the infrared light source (29) fully illuminates only one of the sensors (4, 36 or 5, 37). The full illumination zones (22, 23) do not spatially overlap beyond the limit distance (20); and the window width (41) is smaller than the sensor coverage zone (17) in the direction of motion (30).