Using a Motion Sensor Light Switch

A closeup shot of a motion sensor light switch on the wall

Brett Holmes Photography / Getty Images

Standard light switches aren't exactly hard to use. Most people flip them on without a thought. But what if you walk into the laundry room with an armload of clothes and can't even see the switch, let alone get a hand free to turn it on? Or when you're carrying a heavy box or bags of groceries from the garage and can't reach the light switch to turn it off? Motion sensor light switches are a wonderful solution. Read ahead for details on what they are and how they are used.

Types of Motion Sensor Lights

There are two basic types of motion sensor switches: active and passive. Active sensors or radar-based lights emit sound waves, waiting for the signal to return. For example, some garage door openers will activate if someone enters the room or moves inside the room because the sensor notices that the speed of the returning sound waves changes—triggering the switch.

Passive sensors are also called passive infrared sensors (PIR) or pyroelectric detectors. They detect body heat from humans and animals. The sensor uses a photodetector, which converts light in the wavelengths into an electrical current. A detectable difference triggers the minicomputer housed in the detector to activate the switch. To prevent nuisance switching, the computer ignores slow changes in room temperature due to sunlight.

Occupancy vs. Vacancy Switches

Motion sensor switches can automatically turn the lights on or off or both. Both occupancy and vacancy switches leave the lights on if they detect motion in the room, so if you're perfectly still, they might turn the lights off. However, there are some differences to note between the two.

Occupancy Switches

Occupancy switches turn the lights on when you enter the room; when you leave, the switch waits a preset time before turning the lights off automatically.

Vacancy Switches

Vacancy switches must be turned on manually but will turn the lights off automatically when you leave the room. If you have kids who tend to leave their bedroom lights on, then vacancy-type motion sensor switches are a good solution. You can also get motion sensor switches with a built-in dimmer, allowing you to set the desired light level manually. This switch is a helpful feature for bathrooms and bedrooms, where you might not want full brightness at night or in the morning or when others are sleeping.

Deciding on a Motion Sensor Light

Of the many reasons for getting motion sensor lights, the three most significant considerations are energy conservation, theft or crime deterrent purposes, and convenience. You can save on energy costs light bulb usage and contribute to a more eco-friendly lifestyle by installing motion sensor lights. It's very easy to forget to turn off lights, for example, in a garage or basement, and you may leave the lights on all night.

If you use floodlighting to guard your house against intruders, keeping a light on all night may not alert you to a change in the perimeter, whereas a motion sensor light turning on might get your attention. Motion sensor lighting outside the house is also handy when taking out the trash, walking the dog at night, arriving home after dark, or leaving in the morning before sunrise.

For convenience's sake, motion sensor lighting will help forgetful family members who leave a room without switching off the light by handling the task. The other benefit is if your hands are full, you don't have to fumble for a light switch, or in some cases, if the light switch is in an odd place or further away, you can eliminate the need to use a switch at all.

In the case of garages and places where you expect to have your hands full, an occupancy switch is your best bet. Vacancy switches or switches that need to be turned on tend to save more energy because the occupant may want to leave the lights off or dimmed to a lower level.


Motion sensor switches are designed to replace any standard single-pole wall switch. Specific wiring configurations vary by product. Some switches include a neutral wire connected to power the LED, while others do not (standard switches typically do not connect to the neutral circuit wire). Be sure to check the wiring schematic that comes with your specific model of the switch to ensure you wire it correctly.

In a typical installation, the motion detector switch has three wire leads. The black lead connects to the incoming "hot" wire that supplies the power to the switch. The blue lead connects to the outgoing circuit wire connected to the light; this is called the switch leg. The green lead is the ground and links to the circuit's ground system.


Before you start any wiring work, turn off the power to the fixture at the main panel. Test the wires to make sure the current is off by using a voltage tester to test the ground wire (green), hot wire (black), and neutral wire (white).