The sensor is designed to detect motion from a heat emitting source (such as a person entering a room) within its field-of-view and automatically switch lights ON. These sensors have multi-segmented lenses. For units to sense motion, the person must cross between two segments. The distance between segments increases the farther you are from the sensor, so motion has to be larger the farther you are from the unit. PIR sensors are considered line of sight sensors, meaning that the sensor must be able to have a direct line of-sight to the person making the motion. The sensor includes self-adaptive technology that continuously self-adjusts sensitivity and Time Delay in real-time, maximizing the potential energy savings that are available in the particular application. In Automatic On Mode, the lights turn ON when a person enters the room. In Manual On Mode (R model only), the lights are turned ON by activating a momentary switch (model # GMDS- ) that is connected to the sensor. The MicroSet Passive Infrared Low Voltage Ceiling Sensor has an ambient light level sensor. When enabled, the day lighting feature (R units only) prevents lights from turning ON when the room is adequately illuminated by natural light.