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How do motion detectors work?

Edited by Amy Reeves

If you want to bolster your home security system, a motion detector is a vital component. Motion detectors come in different shapes and sizes, but most feature either passive infrared (PIR) or microwave sensors, allowing them to inform the members of a household whenever something moves in their home.

Some of the best motion detectors on the market can give homeowners insights into the activity in their homes and offer additional peace of mind. Motion detectors vary in price, with models ranging from £20 to upwards of £100 depending on the brand, model and features. This wide scope makes them ideal security devices for the budget conscious.

In this article, our expert team deep dives into motion detectors, explaining what they are, how they work and what the benefits are so you can make an informed decision on your home security.

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How do motion sensors work?

In a nutshell, a motion detector can alert the homeowner or set off various actions, such as turning on a light or locking a smart lock, if it detects a person or movement in the room it is placed in.

Motion detectors have evolved massively over time. Thanks to the inclusion of PIR and microwave sensors, motion detectors have become more accurate and accessible to the general public. Detectors can now be linked up with some of the best home security systems on the market for further control and safety, with some models featuring remote access and notifications that are sent to the homeowner immediately.

Some motion detectors can differentiate between household pets and humans, which ensures that you won’t be inundated with false alarms throughout the night. They do this by disregarding movements from objects under certain weights, so you can rest easy knowing that your cat won’t trigger a set of alarms.

Different types of motion detectors function in specific ways, which the next section will touch on, but they all offer similar features and allow homeowners to gain a better understanding of what is happening in their homes.

What are the different types of motion detectors?

Knowing the difference between motion detectors is crucial, as you want to invest in a device that’ll work for your home. The most common types of detectors are PIR and microwave, but several other options on the market may be better suited for your needs.

PIR sensors

PIR sensors are some of the most popular types of motion detectors. These detectors monitor the infrared radiation in a room, otherwise known as the radiant heat. PIR devices contain two separate sensors that work in conjunction with each other; one measures the ambient temperature in a room, and the other detects any changes that occur. Mammals produce heat, so the sensor can recognise if a human or animal enters the space, as the heat signal will change.

If you have a pet, you should consider a pet-friendly PIR sensor, as you don’t want your motion detector alerting you if a cat or dog happens to walk past. Some sensors can be configured to ignore heat signals up to a certain weight, disregard specific motions or only operate in certain zones within a room to reduce the chance of a false alarm.

PIR sensors work during the day and night and are generally less expensive than microwave sensors. However, due to the nature of PIR sensors, they are less effective in warmer climates, and their ability to detect movement falls dramatically if the ambient temperature is over 35 degrees Celsius.

Microwave sensors

Microwave sensors are the second most common type of motion detector. As the name suggests, they use microwaves to scan the environment. Microwaves are emitted constantly to measure the distance between the sensor itself and all other objects in the room. If an object moves and the distance changes, the motion detector will notify the homeowner.

Microwave detectors are generally more expensive than PIR sensors and are highly sensitive, giving them a wide range of detection. The main drawback of microwave sensors is that they can be too sensitive, even detecting movement through walls, which can result in more frequent false alarms. This makes microwave detectors less effective in smaller rooms than PIR detectors.

Dual sensors

Dual sensor detectors combine the technology of PIR and microwave sensors. Both sensors work in tandem to verify one another, which makes them more effective and less susceptible to false alarms.

In the same vein as the other two types of detectors, dual sensors will notify the homeowner if movement is detected in a room for an extra layer of security.

Key features of a good motion sensor

When looking for a motion detector, there are a few factors you should look out for:

  • Home security: some home security systems come with a motion detector. Our top pick for a home security system, SimpliSafe’s The Tower, comes with a motion sensor for additional security measures
  • Sensitivity adjustment: some motion detectors allow you to adjust the sensitivity, including configured zones or the option to disregard movement under a certain weight to avoid sensors being set off by animals in the home
  • Compatibility: a good motion detector will integrate with your existing home security system, if you have one, and work alongside these devices to provide further peace of mind and additional surveillance in any given room
  • Value for money: you want to ensure that the motion detector you invest in fits in with your own budget and offers adequate features and functionality for the needs of your household
  • Suitability: if you live in a warmer climate, a microwave sensor will be more effective in your home than a PIR sensor. On the other hand, if you want to monitor a smaller room, a PIR sensor will be more accurate. Balance the advantages and disadvantages of each type of motion detector to understand which model will work best
  • App: invest in a motion sensor that can be controlled through an app on a mobile device for ease of use

Benefits of installing motion detectors

There are myriad benefits to installing a motion detector in your home, some of which you may not be aware of:

  • Improved home security: a motion detector allows for additional security within the home; any movement will be detected, and you will be notified, giving you more control over who’s in your space at any given time
  • Enhanced surveillance: extra surveillance means you can check in with your pets or people in your home, as you’ll be informed if they start to move around
  • Convenience: some of the best motion detectors can be integrated with other smart home products, such as smart locks, thermostats or lights, allowing them to be turned on or off when the motion detector is triggered
  • Versatility: you can place motion detectors inside or outside of the home depending on the type you invest in. Wireless models are portable, so you can place them wherever you deem fit

How much do motion sensors cost?

When bought as a standalone product, motion detectors are relatively inexpensive gadgets. The price ranges from £20 to upwards of £100, however, they can be more affordable when purchased alongside a home security system.

Some of the brands that include motion sensors in their home security systems include:

Motion Sensors FAQs

Motion detectors should ideally be placed in a high spot and, if possible, in a corner. This placement allows for high coverage in a room and makes them harder to spot. While placing them near a door or a window may seem intuitive, it can block the range and result in false alarms being triggered by movements outside the house.

If you place your motion sensor outside, ensure that you follow the instructions on the box, such as keeping it away from direct rainfall. It should also be placed at a high vantage point that gives it a good view of your driveway or any paths you wish to secure.

In a nutshell, motion detectors do not usually include camera modules, although some camera devices can be found with motion detection features.

Since dedicated motion detectors use sensors to track movement – whether that be microwave, PIR or dual sensors – they don’t need a camera. Some security cameras do feature motion detection as an additional feature, but these work by tracking movement through the camera, which can be less accurate, but allows the homeowner to keep a record of what’s been happening in their home.

Yes, motion sensors do require a constant power supply, whether that be from batteries or directly from an outlet. Wireless motion sensors can be placed in more discrete locations and come with the benefit of portability, with hardwired detectors being more reliable since they will only run out of power if you experience a power outage.

Gemma Ryles

Home Tech Writer

Gemma Ryles is a BJTC and PPA-accredited journalist with three years of experience writing across various publications. As a home tech expert at Independent Advisor, Gemma tests, researches and writes about broadband and home security. 

Previously, Gemma reviewed and curated lists about consumer technology at Trusted Reviews, where she honed her skills in creating buying guides and features to help customers make informed decisions. She has previously worked at Yorkshire Post, BBC Yorkshire, Glitterbeam Radio and Bonus Stage. 

Gemma has a BA in Journalism and in her free time can be found writing short stories, gaming and crocheting. 


Amy Reeves


Amy is a seasoned writer and editor with a special interest in home design, sustainable technology and green building methods.

She has interviewed hundreds of self-builders, extenders and renovators about their journeys towards individual, well-considered homes, as well as architects and industry experts during her five years working as Assistant Editor at Homebuilding & Renovating, part of Future plc.