6 (Important Facts) How Do Motion Sensors Work And Much More

Motion sensors are found in structures all over, including in businesses and in homes. Motion sensors can be used to trigger an alarm, open a door or window, send an alert to you via an app, or even trigger an automatic phone call to a security guard. However, there are many kinds of motion sensors, so the kind you choose to have in your home or business may depend on your budget, what you’re using the motion sensor for and other factors. I’m here today to tell you a bit about how motion detectors work. Knowing the mechanics behind motion sensors can help you decide which type of sensor is best for your purposes.

How Do Motion Detectors Work?

Alarm system - cameras and sensors

Motion sensors work by detecting a type of energy, a wave, or something else that’s measurable in the environment that might change when an object moves. There’s not one type of way that a motion sensor works because different types of motion sensors will measure and are triggered by different things.

#1. Microwave Motion Sensors

Microwave motion detectors send out microwave pulses to bounce off objects in the area around the sensor. The sensor uses the microwaves to measure the distance between itself and the other objects in the room. Moving objects create variation in microwave measurements, triggering the alarm.

These devices are more commonly used in commercial settings because they can measure larger spaces than some other products on the market. They’re also a little more expensive and exceed many homeowner budgets.

Potential Pitfalls: Microwave detectors can experience interference from electrical pulses. Read the instructions and manufacturer notes carefully before installation to prevent problems, or have them installed by a professional.

#2. Passive Infrared Motion Sensors (PIR)

Passive infrared motion sensors are the kind of sensors most commonly used in homes and residential settings. PIR devices, and even outdoor PIR motion sensor, measure heat by seeking moving objects giving off more heat than other objects in the background. The object must be moving and in motion, or the PIR won’t detect it, so appliances and other objects that give off heat won’t trip the alarm.

#3. Ultrasonic Motion Sensors

Ultrasonic motion detectors work similarly to microwave sensors. They send out ultrasonic pulses that bounce off objects and reflect back to the sensor. The sensor uses the returning pulse to measure the distance between the objects in the room and the sensor. When measurements change, this triggers an alarm. At one time, ultrasonic motion sensors were popular, particularly when motion sensors were first invented. Today, they’re less common.

#4. Area Reflective Motion Sensors

Area reflective motion detectors are similar to the ultrasonic and microwave sensors, but instead of using ultrasonic pulses or microwaves, area reflective sensors use an LED light to emit infrared rays. As the rays bounce off of objects in the room and return to the sensor, the sensor measures the distance between itself and the objects in the room. When the distance changes, the alarm is tripped.

#5. Vibration Motion Detectors

Vibration motion sensors measure the vibrations in a structure. When the vibrations reach a pre-set threshold, the alarm goes off.

#6. Multi-Technology Motion Sensors

Multi-technology motion sensors are exactly what they sound like: they’re motion sensors that use more than one type of motion detection technology to reduce the chance of a false alarm and accurately measure the presence of a moving object in the room. Usually, multi-technology sensors will combine a passive type of motion sensor (like PIR) with an active type of motion sensor, like microwave technology.

What Else Do You Need to Know About Motion Sensors?

Motion Sensor

There’s quite a lot more to motion detectors than just the basic functionality. Before buying a product, you should understand the limitations of each device, and know-how to avoid problems like false alarms. Proper installation is important. Plus, if you’re a homeowner with pets, the activities of your animal friend should be taken into consideration before making your purchase. Below, I’ve answered some frequently asked questions that can help you make an informed decision when you’re trying to purchase a product. I recommend reading all the questions that apply to you, and I recommend doing more research before making a purchase.

#1. Do Motion Sensors Have Blind Spots?

A person who understands how a specific type of motion sensor works may be able to fool the sensor. Slow-moving objects, moving objects hidden behind other objects in the room, and moving objects that are short enough to evade detection by the motion sensor may be able to infiltrate the area while avoiding detection.


  • Install a multi-technology device. Multi-technology devices were invented to cover all the bases. Installing a multi-technology device makes it more difficult for someone to invade your space without being detected.
  • Install multiple devices in one space. The more devices that you use in one space, the harder it becomes for someone to invade your home or commercial building. Cover the area thoroughly with sensors, including some out of the way places (like from the ceiling or behind furniture).
  • Keep your motion sensors hidden. Some people know how to get past motion sensors. However, people are less likely to avoid tripping motion sensors if they have no idea the sensors are even there.
  • Use other devices to protect and secure your home or business. Use a mixture of security cameras, motion lights with alarm, motion-activated infrared camera, garden motion sensor, smart doorbell technology, window sensors, glass break sensors and other devices to keep your home or business safe.

#2. How Are Motion Sensors Installed?

Close-up Of A Young Male Electrician Installing Security System Door Sensor On Wall

Some motion detectors are professionally installed by security companies. Find out before signing a contract whether installation comes with the subscription, or if you’ll be paying a separate charge. If you’re a homeowner, there’s a good chance you’re planning to install your own motion sensors. There are a variety of reliable products available on the market. Pick the product that’s right for you. Before making your purchase, do your research. Here’s what you should know before you buy:

  • What kind of motion sensor is it?
  • Does it get good reviews?
  • How long has it been on the market? (Is the product tried and true?)
  • Does it fit in your budget?

Once you’ve made a purchase, read the manufacturer instructions before attempting to set up the product. Always defer to the manufacturer’s instructions, even if the instructions contradict other advice you’ve read elsewhere. The manufacturer knows best.

Choose the Right Location

Motion sensing technology works best when it’s installed in the correct place.

  • To prevent false alarms, stay about 10-15 feet away from heat registers, sunny windows, hot appliances, and radiators.
  • Make sure your motion sensor is installed up high whenever possible, but not on top of large pieces of furniture. Most motion sensors can be easily mounted to the wall.
  • Motion sensors work best when installed on corners to cover as much square footage as possible.
  • Install sensors in locations where people must pass through in order to enter your home or reach your most valuable possessions.
  • Use multiple sensors in different locations to cover sensitive areas like entrances and bedrooms.
a motion sensor installed at the side of the wall

Once you’ve selected the areas of your home where sensors will be installed, turn on the sensors and test them out with the software that controls the automatic sensors. Most products are now controlled via an app on your mobile device, computer, tablet, or on multiple devices at once. Once the app is installed and the sensors are activated, many systems walk you through the installation process step-by-step. If you’re not especially computer savvy or if you have bad luck performing these types of installations, choose a product that is known for being easy to set up.

To ensure good coverage of each room, pair your product with other products like a security camera, break glass sensors and door entry sensors. Remember that motion sensors can’t detect all problems that could occur with your home. Installing more than one security device on your property will help ensure that you’ll be able to monitor your home every day, at all times.

#3. Who Needs Motion Detectors?

Motion sensors are for people who:

  1. Have something to protect or monitor
  2. Live or work in a high-risk area
  3. Want a peace of mind while away from home or work

You may not think that you’re at risk of a break-in, but if you’ve ever been on a vacation and have worried about what was going on at home or in your commercial building, then motion detectors may be right for you. You’d be surprised how affordable and easy to install motion detectors have become. With the invention of smart technology, people have the ability, more than ever before, to gather data from remote locations and make informed decisions based on the data they collect. Installing motion-sensitive devices on your property gives you the ability to monitor and protect your home or business, even when you’re not there.

#4. What If You Have Pets?

Some motion detectors are designed to ignore pets. Most of the time, these devices measure the height of a moving object and only trip the alarm when a moving object of a certain height enters the monitored space. These devices are not fooled proof, however. For example, if you have a dog who jumps up in excitement when the mailman arrives, or maybe a cat who will not stay off the furniture, then false alarms are likely. I recommend installing other devices, maybe some security cameras and break-glass sensors, to monitor your activity at home.

Another fact worth noting is that anyone who crawls into the room at the height of a pet may be ignored, much like a pet. That said, many dogs will not greet strangers who crawl on hands and knees in a polite or friendly way, so depending on the type of pet you own, your bases may be covered anyway.

#5. What Should You Do to Maintain Your Motion Sensor?

Most motion sensors need to be cleaned regularly or dust can impact their ability to function. Read the manufacturer’s instructions about maintaining your motion sensor, and clean them periodically to remove dust. If your motion sensor stops working at any point, this could be related to dust on the lens, or it could be a software problem.

Your sensors likely come with a book that will help you identify common problems, so you can keep your sensors working without getting help from a professional. If you’re not comfortable maintaining your own sensors, then you might be happier signing a contract with a security company that will maintain the sensors for you. Find out about their maintenance practices before signing the contract, to ensure that you won’t have to pay extra for them to troubleshoot problems or come out to maintain their equipment. The best companies will often stand by their equipment without nickel and diming you for the repair.

I’m Here to Help, If You Need It

If you enjoyed this explanatory article and found it useful, I’d love to get your feedback. Tell me what else you’d like to read about in the future. I’m listening!

Motion sensors are useful for homeowners and business owners who want to protect their property using some DIY technology. These devices also help you monitor what’s going on at home or work without actually being present. They enable you to be in two places at once, and to act if something starts to go wrong in the place being monitored. Whether you live or work someplace that may be high risk for intruders and burglary, or you simply want to keep an eye on your pet or children while they’re at home, motion sensors are a tried and true technology, available at an affordable price.

If you have questions, leave your comments in the box below. I’ll be happy to talk!

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About John Fox

ebbb364ee14268bd3b77496cab3d1d78?s=90&d=mm&r=gCertifications: Certified Alarm Technician (CAT)
Education: Denver Security Academy
Lives In: Denver Colorado

John Fox has worked as a security consultant in Denver for over 20 years.
With Safe Now, he's taken those two decades of experience and decided to share it to help people online make the right security decisions for their businesses and families.

John writes security tips and guides, product recommendations, and prevention guides.

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