A defined space in front of the sensor within which object detection takes place. The Hyde Park Model SM600 family of proximity sensors have fixed sensing windows (widths) ranging from 51 mm (2") to 178 mm (7") for the SM600 series; 102 mm (4") and 152 mm (6") for the SM606 analog series; 51 mm (2") and 152 mm (6") for the SM607 series.