Abstract: Occupancy sensors are presented that include a flat lens for focusing detecting beams into narrower, longer range beams than those of conventional curved lenses. A sensing circuit generates a detecting beam that is substantially perpendicular to the flat lens. The flat lens has a plurality of lens segments that provide long, intermediate, and short range sensing beams. To facilitate positioning of an occupancy sensor, the sensor includes a plurality of indicators that indicate the sensor's long and short range sensing limits. An override timer circuit is provided that upon activation sets the occupancy sensor in occupancy mode for a predetermined time period. A warm-up timer circuit is also provided that upon power-up automatically sets the occupancy sensor in occupancy mode for a predetermined warm-up period. These occupancy sensors are well-suited for environments with long aisles, high ceilings, and high intensity discharge lighting.