Motion Sensors Guide 2021

Helloooooo, motion sensors!

If your motion sensor knowledge comes purely from sci-fi novels and heist movies, you’ve come to the right place. We’re about to explain what motion sensors are, how they work, whether you need them, and how you can get them.

Sound good? Then let’s jump into this motion sensor guide.

What are motion sensors?

Motion sensors detect human movement.

These sensors sound like the stuff of fiction, but they’re not. Motion detectors sense the movements of humans and sometimes animals. Detectors are commonly used for security purposes because they’re a great way to know if someone is somewhere they shouldn’t be.

Broadly speaking, motion detectors are easier to use than cameras because you don’t have to monitor them to see if anything’s going wrong. However, you can combine a motion detector and a camera for the ultimate security experience.

How do motion sensors work?

Let’s talk about how motion sensors work their magic.

Home security motion sensors use different types of radiation and light emission to sense human and animal movement.

Types of motion sensors

There are several different types of motion sensors floating around. Some types show up more in home security than others.

Passive infrared

A passive infrared sensor (PIR sensor) is one of the most common types of motion detectors. This sensor detects body heat AKA infrared radiation.¹

Passive infrared demo

Active infrared

An active infrared sensor has two pieces. Infrared light emitted from one piece reflects onto the other. When the beam is interrupted, the alarm goes off.²

Infrared light is usually invisible, so active infrared sensors can slip by unnoticed.

Some people use the terms “active infrared sensors” and “area reflective sensors” interchangeably.
Active infrared demo
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Laser sensors
You know those spy movies where characters have to duck, weave, and flip around red laser sensors? Those lasers are a type of photoelectric motion sensor. They work similarly to active infrared sensors but with a visible beam of light.

Photoelectric sensors like these are extremely uncommon in home security (and outside of movies in general).


Despite what it sounds like, microwave motion sensors aren’t motion detector–oven combos that can heat up your pizza rolls while detecting intruders. Instead, they use electromagnetic radiation to look for moving objects.³

Microwave demo

One nice thing about microwave motion sensors? They can be calibrated to be more or less sensitive, which is especially useful if you have roaming pets.

Ultrasonic and tomographic sensors are similar to microwave sensors, but they use high-frequency sound waves and radio waves instead of electromagnetic waves.⁴

Dual technology

Dual sensors use two different technologies. For instance, this sensor from Napco uses both microwave and passive infrared detection.

Further reading

Do you need motion sensors?

Not every home needs a motion sensor.

Now that you know all about motion sensors, the next question is, do you need them?

You don’t have to meet a specific threshold to qualify for motion sensors. But if you’re going back and forth on whether the expense is worth it, here are a few situations in which you probably do want sensors.

You’re wary of home intruders.

Most people who use motion sensors use them as part of a security system. They put them in highly trafficked locations or valuable-filled rooms.

In those cases, the users usually only arm the motion detectors when they’re out of the house.

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Is a contact sensor a motion sensor?
A door/window sensor (also called a contact sensor in some cases) is not quite the same as a motion detector. A contact sensor relies on a pair of magnets to sense motion. It sets off its alarm only when the magnet is separated by a door or window opening. The sensor can’t detect independent human motion.

You live with people you don’t trust.

That sounds sinister, but it doesn’t have to be. You might get a motion sensor purely to keep your roommate out of your minifridge or your teen in their room at night.

You can also use a motion detector in a gun closet, a liquor cabinet, or the front room that your kid and your cat aren’t allowed in.

You want to keep track of your kids or pets.

Some motion sensors can send you notifications without triggering an alarm. These kinds of sensors can be useful if you want to know where your kids or pets are while you’re gone or busy in another room.

In these cases, you generally want to put the sensors in most rooms to track movement throughout the house.

Where do you get motion sensors?

There are a few different ways you can get your hands on some motion sensors.

You have two choices when it comes to obtaining motion sensors. You can buy some standalone sensors and jury-rig a piecemeal security system. Or you can buy a preassembled home security kit that includes at least one motion detector. List Prices (as of 12/08/2020 3:30 MST) Full disclaimer

Most national security providers offer both standalones and kits.

Motion sensors from security providers
NameImageStandalone priceLowest kit priceLink
SimpliSafeSimpliSafe Motion Detector$29.99$229.00View Plans
FrontpointFrontpoint Motion Detector$29.99$99.00View Plans
Link InteractiveLink Interactive Motion Detector$50.00No kitsView Plans
AbodeAbode Motion Detector$55.00$229.00View Plans
Ring$29.99$199.99View on Amazon

Prices as of 08/02/2021. Offers subject to change.

You can usually buy your motion sensors online, but every now and again, you’ll run into a provider that requires you to call in to order.

Further reading

How do you install motion sensors?

Most motion detectors are easy to install.

In the past, motion sensors tended to have wires. Now they’re usually wireless—easy for anyone to install.

If you order a motion sensor from a company that does professional installation (ADT comes to mind), a technician will usually install it. Otherwise, it’s all you.

Installing a motion sensor generally goes something like the following:

  1. Find a place to put the motion detector. Many providers recommend placing the detector in a corner, six to eight feet above floor level.
  2. Follow the manufacturer’s instructions to fasten your motion detector in place. Many DIY motion sensors are peel-and-stick, so you don’t need any brackets or tools.
  3. Follow the manufacturer’s instructions to activate the detector. This usually involves some kind of app.
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Can I put my motion detector outdoors?
We don’t recommend exposing a motion detector to the elements unless it’s specifically labeled for outdoor use. Most of the outdoor motion detectors we’ve seen are built into outdoor cameras or motion-activated security lights.

Further reading

How do you get home automation support for your motion sensors?

Connect your motion detector to your smart home suite.

We love telling a smart assistant to arm home security devices. It’s easy to do as you run out the door or settle down for a good night’s rest.

You can get the convenience of a voice assistant for some, but not all, motion sensors. We’ve put together a list of compatibility for some of the most popular motion detector brands.

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Top voice assistants
The best-known voice assistants are Alexa, Google Assistant, and Siri.

Motion sensors that work with Amazon Alexa*:

  • SimpliSafe sensors
  • Frontpoint sensors
  • Link Interactive sensors
  • Abode sensors
  • Ring sensors
  • ADT sensors
  • Blue by ADT sensors
  • Google Nest sensors
  • Cove sensors
  • Scout sensors

Motion sensors that work with Google Assistant*:

  • SimpliSafe sensors
  • Frontpoint sensors
  • Link Interactive sensors
  • Abode sensors
  • Ring sensors
  • ADT sensors
  • Blue by ADT sensors
  • Google Nest sensors
  • Cove sensors
  • Scout sensors

Motion sensors that work with Apple HomeKit*:

  • SimpliSafe sensors
  • Abode sensors

* Not complete lists. Also, some providers’ motion sensors may work with smart assistants only when hooked to the alarm system hub.

Some motion sensors can also be linked directly to other smart equipment, like lights, locks, or plugs. These connections are usually made through Z-Wave or Zigbee protocols.

Further reading

Recap: How to choose a motion sensor

Let’s review what we’ve learned about motion sensors.

Now that you know the facts about motion sensors, you might be interested in buying one. Let’s quickly walk through the process you’ll need to follow.

Decide whether you need a motion sensor: It makes more sense for some people to buy a motion sensor than others. If you have security concerns or need to keep an eye on certain parts of your house, a motion detector is probably a good fit.

Choose a sensor: You can select either a standalone sensor or a sensor associated with a home security system.

Install your sensor: Some sensors are professionally installed, while others are DIY. In today’s world, most DIY sensors are relatively easy to install.

Connect the sensor to your smart home: If you want a fully automated home, take advantage of your sensor compatibility to link it up to some other equipment.

Further reading


  1. Wikipedia, “Passive Infrared Sensor.” Accessed August 14, 2020.
  2. Danny Jost, Fierce Electronics, “What Is an IR Sensor?” July 29, 2020. Accessed August 14, 2020.
  3. Protect America, “What is a Microwave Motion Detector: A Quick Guide.” February 28, 2018. Accessed August 14, 2020.
  4. Wikipedia, “Motion Detector.” Accessed August 14, 2020.

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