The Wattstopper FS-505 is a low voltage ultrasonic fixture occupancy sensor designed for stairway applications, mounting directly to the fixture at 120/277VAC. Ultrasonic technology ensures reliable occupancy detection in challenging stairwell geometries where PIR coverage is limited. The low-profile form factor integrates cleanly into commercial fixture housings and operates via the FS Low Voltage Sensor series with 24VDC supplied through an RJ45 connector from a compatible FS-PP power pack.