What is the definition of a motion sensor light switch? Motion sensor light switches are devices that detect movement in an area and then turn on the lights associated with that area. They are typically used in hallways, stairwells, and other places where light is often needed. Motion sensors are typically connected to a light switch, so that when someone enters the area, the sensor will detect movement and turn on the lights. This can be a great way to save energy, as the lights are only on when there is someone present in the area. Motion sensor light switches are very easy to install, and they can be set up to turn on the lights at different times of the day. They can also be programmed to turn off the lights when no one is present in the area for a set amount of time. Motion sensor light switches are very convenient and can make life easier for those who are conscious about energy consumption.