A method of installing a projected beam detector can include providing a radiant energy source, providing a reflector, and projecting a radiant energy beam from the source to the reflector. A multi-pixel sensor or camera can be provided. The beam can be reflected from the reflector back to the sensor. A distance between the reflector and the camera can be determined based on a size of an image of the reflector incident on the camera. Where incident intensity corresponds to expected intensity for a predetermined distance, a sensitivity can be set based on the predetermined distance.