The RPS-450, 475 are stud-mount, completely self-contained, 120VAC powered ultrasonic proximity sensors. These sensors are range or distance sensitive, enabling the sensors to detect objects only within the desired range and rejecting others. The RPS-450, 475 are solid state sensors including their solid state outputs, therefore having nearly unlimited life. The sound source operates in the ultrasonic spectrum and is therefore not heard. For initial setup purposes, a built in potentiometer and LED indicator are provided. The LED indicator illuminates when the ultrasonic wave from the sensor is reflected back to the sensor within the preset range. These sensors provide precise proximity or level sensing regardless of color, density, or transparency. They are equally effective on liquid, metal, plastic, and glass targets.