How Do Occupancy Sensors For Home Lighting Work?

If you have a smart home, you probably have it for one of two reasons. You either want a home that is streamlined to the utmost convenience, or you want to save money in the long run. 

Possibly, you have considered both factors in your decision to make your home smart. Occupancy sensor switches fall into a device category that fulfills both purposes. 

What is an occupancy sensor switch?

Occupancy sensor switches are devices that sense whether a space is occupied. They can automatically turn off the lights if a room is vacant. They can also automatically turn the lights on when somebody enters a room. This has many possible advantages. 

A few different types of technologies are used in smart lighting occupancy sensors. 

Occupancy sensors for smart lighting detect whether a room is occupied. Most use either passive infrared (PIR) or ultrasonic (US) technology. Dual-technology sensors combine PIR and US technology. Understanding the pros and cons of each will allow you to select the right sensors for your home.  

Each sensing technology has pros and cons and may be more or less appropriate for a specific room in your home. In this blog post, I explore how these sensors work and how you can use them in a smart home. 

How occupancy sensors for smart home lighting work  

All occupancy sensors for the home detect motion in a room. They respond by signaling to lights in the room to turn, or stay, on or off. Yet, how they detect motion differs for different devices. 

What is the difference between a motion sensor and an occupancy sensor?

A motion sensor only detects a body when it is moving. An occupancy sensor detects the presence of a body in a room, even when stationary. The two terms are often used interchangeably when referring to smart light sensors. Devices sold as motion sensors may be able to detect occupancy. 

I describe aach technology in more detail below. The technologies are quite complicated and some of these explanations are rather technical. If you’re more interested in how to use occupancy sensors in your home, you may want to skip to the next section. 

Passive infrared (PIR) occupancy sensors

Infrared sensors are passive because they do not actively send out infrared waves. Instead, they track the heat in a room by detecting infrared radiation. Human (and animal) bodies radiate heat energy in the form of infrared radiation. 

A PIR consists of a pyroelectric sensor attached to a circuit board. A pyroelectric sensor generates energy when exposed to heat. The sensor has two slots, each of which senses infrared radiation. 

The pyroelectric sensor is covered with a multi-faceted Fresnel lens. This lens focuses the infra-red radiation onto the two slots.

Occupancy-based strategies can produce average lighting energy savings of 24%. This is according to the Lawrence Berkeley National Laboratory.

The shape of the lens results in the radiation being detected from fan-shaped zones.  When there is no movement,  the different zones emit equal infrared radiation. The two slots will receive the same amount of radiation. 

When there is a movement across the zones, heat waves of different frequencies are emitted from the moving body in the different zones. These heat waves are concentrated by the lens onto the two slots of the sensor. 

The pyroelectric sensor has a pre-set temperature limit. When this limit is surpassed, a signal is created. The difference in energy received by each slot informs the sensor that there is motion. 

If motion is detected, an electrical signal is sent from the pyroelectric sensor to a circuit. This turns on the lights.

These sensors are better at picking up lateral movement. Full body movement is also more easily detected than a simple hand movement. 

The further away the movement is from the sensor, the lower the lens’s ability to detect the motion will be. 

PIR sensors must be stimulated by infrared radiation to detect occupancy.  Infrared energy cannot pass through objects. PIR sensors thus cannot detect occupants around corners or behind glass (because ).

Ultrasonic (US) Occupancy Sensors

Ultrasonic occupancy sensors are called active sensors as they emit ultrasonic energy waves. 

These waves have a high frequency. They bounce off objects in the room and return to the sensor. If there is movement in the room, the waves bouncing off the moving object change in frequency. The sensor picks up this change in frequency and interprets it as movement. It then responds by switching on the lights (or leaving them on if they are already on). 

Alternatively, an ultrasonic sensor can set up a standing wave. It can sense changes in the amplitude and frequency of the wave. These changes would occur if there were motion in the monitored area. 

Most ultrasonic occupancy sensors emit waves of 32 to 40 kHz frequencies. These are higher than what the human ear can hear and thus cannot be heard. The frequency is also high enough to avoid interference with hearing aids.

Ultrasonic waves can pass through objects and glass. Thus, US sensors can pick up on movement even if the moving body is behind an object (like a cupboard) or glass. 

Dual Technology (DT) occupancy sensors

DT occupancy sensors make use of more than one technology for detecting movement. This improves accuracy. 

Many DT sensors have ultrasonic and passive infrared technology to sense occupancy. 

If both the PIR and US systems detect movement, lights will turn on. Only one of the two systems needs to detect movement for the lights to remain on. 

There is also a type of DT sensor, a passive DT sensor, that has PIR technology and acoustic detection. These sensors listen for sounds in the space and respond to them. They can discern between white noise and significant noises in the monitored space.

XCT technology from Lutron is found in the Lutron Maestro Motion Sensor Switch. It allows the sensor to distinguish between background noise and motion quite accurately. This improves the accuracy of occupancy sensing.  

The following types of occupancy sensors are less common. 

Microwave occupancy sensors

Microwave sensors emit low-power microwaves to detect motion. 

Camera-based occupancy sensors

Camera-based sensors take many photographs of the area every second to detect occupancy.

What is the difference between vacancy sensors and occupation sensors?

Vacancy sensors and occupancy sensors work by detecting whether a room is occupied. However, while a vacancy sensor causes lights to switch off when a room is empty, it does not turn on automatically when sensing motion. It must be turned on manually. This saves electricity during the day. 

You also get partial-on sensors. These automatically turn on lights when motion is detected, but the lights are only switched on to a 50% brightness. The occupant can then increase the brightness manually at the switch. 

Where should occupancy sensors in your home be placed?  

Occupancy sensors can be integrated into wall switches. They can also be attached to the ceiling, placed high up on a wall, and mounted to lighting fixtures. 

There are wireless and wired options, depending on where you would like to place the sensor. 

When placing your occupancy sensor in a room, try to put it in a location where it can cover a maximum area in the room. However,  also be aware of locations where the sensor may detect movement outside the room. 

For example, you wouldn’t want your sensor to be placed where it can detect movement from an open door. This would result in lights turning on in the room every time somebody walks past the door. This would waste electricity. 

Occupancy sensors can be placed in the living room, kitchen and bedroom. Other great locations are utility rooms, walk-in closets, and basements. 

Benefits of having occupancy sensors for lighting 

Occupancy sensors for smart home lighting have several advantages.

1. Convenience 

Occupancy sensors allow you to enter a room without having to switch on a light. You can also leave a room without having to switch off a light. If you are prone to forgetting to switch off your lights, this gives you good peace of mind. 

This is especially convenient for rooms you are likely to enter with full arms, like the laundry room. 

2. Energy savings

As mentioned above, occupancy sensors are practical if you often leave your lights on. This benefit is extended to saving electricity because lights will not be on while nobody is in the room. 

This benefit will be even more evident if you have a sensor that also has daylight sensing. Such a sensor would not switch on a light during the day even if the room is occupied. 

Vacancy sensors also result in greater energy savings than occupancy sensors. 

3. Improved security

Occupancy sensors can improve the security features of your home. They can alert you when somebody is in another room in your home by turning on the lights.  They can also scare off intruders when the lights turn on automatically. 

4. Improved automation

Occupancy sensors can send data about room occupancy to other smart home devices. 

If you have a hub-based smart system in your home, these sensors can “inform” the system if a room is occupied. In response, other devices in your home may respond.

For example, heating systems or air-conditioning systems may be turned on or off. 

What is the best occupancy sensor?

As with most smart devices, there is no one “best” occupancy sensor. There are many variables when comparing different homes. These include room sizes, family members, the presence of pets, budget, and lighting requirements. Homeowners should consider several factors to select the best occupancy sensor for them. 

12 Factors to consider when selecting an occupancy sensor

Consider the following factors when selecting an occupancy sensor for your home:

1. Adjustable sensitivity settings 

The more sensitive a sensor is, the further away it can detect movement. More sensitive sensors can also detect smaller movements such as a hand motion.

Some sensors have adjustable sensitivity settings. This is practical for fine-tuning motion detection in a room. This allows you to avoid false positives or the lights turning off even if there is someone in the room. 

Different sensor technologies have different sensitivity abilities. Consider this when selecting an occupancy sensor. 

2. Maximum coverage area 

The occupancy sensor in each room should be able to sense occupancy throughout the room. Make sure that the sensor you choose has a coverage area that is big enough to cover your room to avoid blind spots. 

3. Dimming abilities 

Some occupancy sensors have a dimming function. This allows you to adjust the brightness of the light. This is great for energy savings. 

If you already have other smart devices set up, it is not necessary for your occupancy sensor to have a dimming switch. Smart switches or bulbs can usually be controlled with an app. The app can be used to change the brightness of the lights. 

4. Pet immunity 

Sensors that have ‘pet immunity’ do not respond to movement of bodies smaller than a set size. This prevents your system from being triggered every time your cat or dog (or other pet) is in the room.  

The Ecolink Z-Wave Plus Motion Detector can “ignore” movement from pets as large as 55 lbs. 

You could just cover the lower part of your sensor to eliminate it being triggered by your pets. You could do this by painting the lower half or sticking a vinyl sticker over it. However, this could be a security risk, so consider this option carefully. 

5. Annunciators

Most sensors have an LED indicator light. This light indicates that motion is being detected. 

Some of these lights can be quite bright, which can be distracting when you are trying to sleep. Check the brightness of the indicator light before purchasing a sensor for your bedroom. 

Some sensors make a soft sound before turning the lights off. This is practical in the case of a false-negative and you are actually still in the room. You can then make a bigger movement to trigger the system and keep the lights on. 

6. Compatibility with light bulbs 

Most motion sensor light switches have a capacity of up to 250 watts for LED bulbs. This is way more than the wattage of a single light bulb.  

However, a light fixture that supports multiple bulbs (such as a chandelier) may have a higher total wattage. Make sure that the sensor can handle the total wattage. 

Also, check whether the sensor is compatible with three-way switches. Some sensors can only be connected to a system where one switch controls a light.  

The Lutron Maestro Motion Sensor Switch is compatible with all types of lightbulbs. This including up to 250-Watt incandescent and 150-Watt CFL/LED. 

7. Compatibility with your home assistant

You may already have other smart devices in your home or are working towards an automated system. In this case, make sure to check which home assistants a sensor is compatible with. 

You want to avoid a situation where you spend a lot of money on sensors and other devices that don’t work together.

Also consider whether the sensors work with Z-Wave or Zigbee and Bluetooth or Wi-Fi.

For example, the Fibaro Motion Sensor has been designed in two lines. One is for the Fibaro system (or other compatible Z-Wave controllers). This one has Bluetooth communication. The other is for Apple HomeKit. This one has Wireless communication. 

It’s important to check the compatibility of your sensors with your other devices. Some manufacturers (like Lutron) do not allow items to be returned after purchase. 

8. Daylight responsiveness 

Some sensors can be set to turn off or not to turn on when they sense sufficient ambient light. This allows for energy saving during the day. 

The ELEGRP Occupancy Sensor Light Switch is an example of an occupancy sensor switch that can detect ambient light.

Check if this setting can be overridden in the sensor you want to buy. Sometimes you want to turn the lights on even during the day if you require extra bright lighting for a task. 

9. Time delay 

Time delay refers to how long the lights stay on after no movement is detected. 

A sensor with an adjustable time delay is practical because you may want to change the time delay based on what you are using a room for. 

Both the Lutron Maestro Motion Sensor Switch and the ECOELER Motion Sensor Light Switch have an adjustable time delay of 1, 5, 15, or 30 minutes. 

10. Occupancy sensors vs vacancy sensors 

Both occupancy and vacancy sensors turn the lights off when no movement is detected. However, vacancy sensors do not turn the lights on when somebody enters a room. 

Occupancy sensors do. With a vacancy sensor, the person entering the room needs to turn the lights on manually. 

Vacancy sensors have the potential to save more energy. You may not need the lights to turn on every time you enter a room, especially during the day. An occupancy sensor with daylight sensing ability can show the same energy savings. 

Many sensors have both occupancy and vacancy sensing settings. One example is the ECOELER Motion Sensor Light Switch. 

11. Ease of installation 

An occupancy sensor may be part of a light switch or a separate device that needs to be mounted to the wall. Consider how difficult it will be to install it. 

Both the Samsung SmartThings Motion Sensor and the Hue Motion Sensor are wireless. This making them exceptionally easy to install. 

Also consider if you will be able to complete the installation yourself. Alternatively if you will need to hire an electrician to do it for you. Hiring an electrician will increase the 

The more sensors you want to install in your home, the more important it is to consider ease of installation. You do not want to struggle with installing six sensors throughout your home. 

12. Compatibility with three-way switches 

Some motion sensors can be connected to a three-way switch, while others cannot. 

It’s worth noting that the motion sensor light switch must be a three-way switch. A single-pole switch can’t be connected to a light that is controlled by more than one light fixture. 

The ECOELER 3 Way Motion Sensor Light Switch is an example of a switch that is compatible with three-way switches. This switch also offers adjustable light and motion sensitivity. 

Tips for installing an occupancy sensor in your home 

Tips for installing PIR occupancy sensors

If you are using a PIR occupancy sensor, a heater in the room may cause a false positive. 

Occupancy sensors should thus not be placed near a heater. Air diffusers and other appliances that emit heat should also not be placed too close to the sensor. 

Air vents such as HVAC vents may create changes in air temperature. This could falsely activate a PIR sensor. Contact with such vents should thus be avoided. 

PIR occupancy sensor sensitivity is reduced the further away a body is from the sensor. The sensor should thus be placed close to the space where the most activity occurs in the room. 

Tips for installing US occupancy sensors

Since US occupancy sensors respond to movement, they should not be installed on sources of vibration. They should also not be placed near air sources such as open windows or air vents. 

Materials that absorb sounds, such as heavy carpeting or ceiling tiles, can reduce the sensitivity of a US sensor. Hard surfaces can improve the sensitivity of the sensor because sound waves can bounce off them better. 

Home Streamliner’s take

I love the fact that an occupancy sensor can switch on a light when I walk into a room with my arms full of laundry, or turn on the lights in my closet when I enter it in the morning. 

For me, occupancy sensors would mainly serve the purpose of convenience. My family is in the habit of turning the lights off during the day, so we probably wouldn’t save much on electricity. 

However, the bonus of being a security feature, for example, that my lights can turn on when I drive into my garage in the evenings, also really appeals to me.


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This blog aims to share my research and first-hand knowledge in a helpful way. My goal is for you to be able to save time and find happiness in a streamlined home.