Understanding How Do Motion Sensors Work?

1 Understanding Motion Sensors and How They Work Desktop

Motion sensors are more common than you might realize. When you ring a wireless camera doorbell, the camera begins recording. When you pull into your driveway at night, your floodlights come on. When someone opens your door, a sensor beeps.

But how exactly do motion sensors work? There are many different types of motion detection sensors, and each operates a bit differently. For instance, the doors that open and close at the grocery store employ a radar-based motion sensor, while a home security motion light may rely on passive infrared technology.

Whether you’re updating your home security system or in the market for new motion sensor alarms, cameras or lights, here’s a full rundown of what motion sensors can do and how you can use them to better protect your home and property.

What technology does a motion sensor use?

Different types of sensors use various forms of technology to achieve the same goal — detecting movement. Here are the main types of detectors and how each works:

Active motion sensors

Also called a radar-based motion sensor, active motion sensors use waves that trip a sensor when someone walks past. Your garage door, for instance, probably uses active motion technology so it can tell if someone or something is in the way when the door closes. Active motion sensors send out arrays of microwave radio energy or ultrasonic sound waves that reflect energy in the same pattern. Disturbances to the pattern trigger the sensor.

Passive infrared sensors

Also abbreviated as PIR, passive infrared sensors detect infrared energy, or body heat, emitted from anyone entering your home. When the sensor identifies energy, it can trigger your intruder alarm and alert police or your monitoring company immediately. However, infrared energy tends to fluctuate, so the sensors trigger when more rapid changes occur in the field — like someone walking into a room.

Photosensor motion detector

Focused light works in combination with a light sensor to detect motion. Say you have a motion detector camera installed on your front porch. If someone travels between the light source and sensor, the blocked beam will trigger the alarm and begin recording.

Infrared motion detector

Everything that has a temperature above absolute zero emits detectable radiation in the form of heat. Heat radiation is invisible to the human eye, but electronic devices such as IR detectors can sense the heat. When a person passes in front of the sensor, the amount of radiation increases because the human’s body temperature is higher than the background temperature. Passive infrared sensors use this infrared technology. In the case of a security doorbell, that heat from a person standing in front of your home triggers the camera to record.

Microwave motion sensor

Often used in radar-based motion detectors, like police speed radar, microwave sensors use safe electromagnetic radiation to emit waves reflected back to the receiver.

Tomographic motion detector

Unlike many detectors that must be within line of sight, you can put a tomographic motion sensor out of view since its waves can pass through walls. Tomographic motion sensors use a webbed network of radio waves that triggers a sensor when disturbed.

What types of motion sensors are out there?

Motion detectors are just one of those many layers but a significant one. Motion detectors can alert you to someone entering your driveway. They can activate motion detector security cameras in and around your home. And motion detector lights will turn on when someone enters a room.

Here are a few motion sensor features to consider when selecting a home security system with motion detection:

Wired vs. wireless

Should you choose a wired or a wireless motion detection system? Well, it depends. Each has its pros and cons. Many motion sensors are wired, meaning they use wires to connect to an alarm system. Wireless motion sensors, however, rely on Wi-Fi or cellular service to alert you of movement.

Features of wired motion detectors:

  • Hardwired motion sensors are more complicated to install and move around.

  • They may need to be near a power source.

  • Overall hardwired security systems are more stable connection-wise, meaning they’re less likely

  • to lose reception or signal.

  • Wired motion sensors are less vulnerable to hacking.

Features of wireless motion detectors:

  • Wireless detectors are easy to install since they don’t require lots of cords.

  • Wireless motion detectors can go anywhere, as long as you have reliable reception.

  • Wireless is only slightly less secure than a hardwired system.

  • Reception and signal stability can be an issue, depending on your Wi-Fi connection, and wireless motion detectors may have a shorter battery life.

  • A wireless system allows for remote monitoring of your home or property via a smartphone or other internet or cellular-connected device.

Contact motion sensors

Contact motion sensors alert you to move in and out of doors or windows. This type of sensor uses two pieces — one against the door or window jamb and one on the actual window or door. When the elements separate, an alert or alarm activates.

Video motion sensors

A video doorbell is an excellent example of a video motion sensor. When the camera senses motion, it automatically begins recording, allowing you to see who’s at the door … or if that package has been delivered.

Pet-immune motion sensors

You want to protect your home, but your cat or dog jumps on a piece of furniture while you’re away and sets off the alarm. Pet-immune motion sensors will pick up human motion but allow pets up to a certain weight limit — usually up to 40 pounds — to avoid tripping the security system. It’s crucial to mount the pet immune motion sensors at the correct position and height to prevent false alarms.

What will set off a motion detector?

While the genius of motion detectors lies in their ability to accurately sense motion, that can be a double-edged sword when you’ve already set your home alarm and you need to run back in the house to grab your keys. Here are a few things that will set off your motion sensors:

Temperature and sound

Even slight changes in temperature can set off your motion detector. If you have your smoke and carbon monoxide detectors hooked up to your security system, you know that temperature can trigger an alarm. A change in temperature could be as innocuous as heated air coming from a floor vent. Aside from heat, a sound disturbance can make motion detection waves bend and set off a sensor.


While pet-immune motion sensors effectively work for pets on the smaller side, what about your 100-pound Golden Retriever? Check with your Senior Security Consultant and calibrate your sensors’ sensitivity and position them to accommodate the pets in your home.

Passing cars

How many times has your doorbell picked up the motion of a car driving down your street or turning into your driveway? To avoid a camera unnecessarily sending an alert to your motion detection app, you’ll want to angle the camera so it’s less likely to pick up your neighbor’s daily runs and or the local lawn company’s truck.


There’s nothing more annoying than a continually beeping sensor when you can’t find evidence of an intruder or motion. Check those backup batteries, and set up calendar reminders to replace them as needed.

Opening and closing doors or windows

Those contact motion sensors rely on two pieces communicating with one another. When they’re disconnected, the sensor sets off an alarm. Make sure no windows and doors are ajar.

Bugs, light, and dust

Creepy crawlies skittering across a motion detection camera may signal the camera to begin recording. As seasons change, light patterns in and around your home may shift, causing shadows that weren’t there when you first set up your motion detection system. Even beams of light with dust motes swirling around can possibly trigger a motion detector, so make sure you keep your camera in a spot that won’t collect bugs or be directly in sunlight.

Wind or AC

Do your drapes brush against your window’s contact sensor when the AC kicks on? Does your outdoor Christmas decor set off your motion detection lights outside? Be mindful of anything that can suddenly move and activate a sensor.

Choosing indoor and outdoor motion detectors is an important piece of your home security system. Whether it’s a fire detector, a water sensor, or door alarm, learn more about Brinks Home™ motion detectors and which options are right for you.

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