The Beginner’s Guide to Motion Sensors

A motion sensor (or motion detector) is the linchpin of your security system because it detects when someone is in your home when they shouldn’t be. A motion sensor uses one or multiple technologies to detect movement in an area.

If you've got a professional home security system, when a sensor detects motion, it sends a signal to your system’s control panel and to the professional monitoring centre, indicating a potential threat in your home.



The role of motion sensors in home security

Role of motion sensors

The main purpose of motion detection is to sense an intruder and send an alert to your device (for DIY security systems) or control panel and monitoring centre (for professionally monitored systems).

Sensors work when you're not home or when you tell the system you are not there. You can even program some security systems to record events via a security camera when there's motion.

Motion sensors stand guard, ready to react to various situations, such as movement in your living room, windows or doors opening or closing, or a window breaking.

Here are some common uses of motion sensors:

  • Alert you in the event that your teenager breaks curfew
  • Trigger a doorbell when someone approaches the front door
  • Alert you when kids enter restricted areas in the home, like the basement, workout room, or medicine cabinet
  • Save energy by using motion sensor lighting in unoccupied spaces
  • Notify you if pets enter areas where they’re not supposed to be

Types of motion sensors

Passive infrared (PIR)

A passive infrared sensor detects body heat (infrared energy) by looking for changes in temperatures. This is the most widely-used motion sensor in home security systems. When you arm your system, this activates the motion sensors to report possible threats.

How a passive infrared (PIR) motion sensor works

Once the PIR motion sensor warms up, it can detect heat and movement in the surrounding areas, creating a protective “grid.” If a moving object blocks too many grid zones and the infrared energy levels change rapidly, the infrared sensor triggers an alarm.

Microwave (MW)

This type of sensor sends out microwave pulses and measures the reflections off of moving objects. They cover a larger area than infrared sensors but are more expensive and vulnerable to electrical interference.

Dual technology motion sensors

Some motion sensors can combine multiple detection methods in an attempt to reduce false alarms. For example, it's not uncommon for a dual technology sensor to combine a passive infrared (PIR) sensor with a microwave sensor.

Dual technology motion detectors use microwaves and passive infrared

Each sensor type operates in different areas of the spectrum (ranging from passive to active). Dual technology motion sensors are not as likely as other types to cause a false alarm, because both sensors need to trip in order to sound an alarm. However, this does not mean that they never cause false alarms.

Less common types of motion detectors

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  • Area reflective sensors emit infrared rays from an LED and use the reflection of those rays to measure the distance to the person or object, allowing for detection when the subject moves within the designated area.
  • Ultrasonic motion sensors measure the reflections off of moving objects via pulses of ultrasonic waves.
  • Vibration motion sensors detect small vibrations that people cause when they move through a room. While you can buy them, they're easy to make at home too. A homemade vibration sensor uses a small mass on a lever, which activates an alarm switch when it vibrates. Homemade motion sensors can work, but they can also be unreliable.

Specialised motion sensors

Contact sensors (door/window)

How contact sensors work

Contact sensors use a magnet to spot movement on a door or window. When the sensor and corresponding magnet move apart as a door or window opens, the sensor triggers an alarm while the security system is armed.

Pet-immune motion sensors

Most passive infrared sensors can ignore animals up to a certain weight. A dual technology motion sensor is more pet resistant to false alarms because it requires two sensors to be triggered a certain way.

Pet immune motion sensors
Light Bulb
Adjustable sensitivity

Some pet-immune motion sensors have an adjustable sensitivity level for homes with energetic pets.

Video motion sensors

Many security cameras use advanced signal processing to start recording when they sense motion. Cameras controlled by motion sensors can save on memory storage by not recording hundreds of hours of useless footage—they only capture the important stuff.

Best practices for mounting sensors

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Wireless motion sensor

Today, most motion sensors are wireless. Wireless sensors are very easy to set up. They do not require drilling, and they communicate with the other security system components wirelessly.

Motion sensor floodlight

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If you choose a security system that requires professional installation, the installer will know how to set up your sensors. However, you are responsible for setting up your sensors if you go with a DIY home security system.

Before you install motion sensors, make sure to read the installation instructions, since they will likely include placement recommendations. Some DIY systems also give you electronic prompts, video tutorials, or have you call a representative to walk you through the setup process.

Keep in mind that motion sensors aren’t error-proof, and there are instances in which there could be false alarms. False alarms are usually caused by electrical failures, user error, poor application engineering, power surges, lightning, and faulty equipment. Animals, insects, and foliage can also trigger them under the right circumstances.

Placement tips

While the best thing you can do to increase the effectiveness of your sensors and prevent false alarms is to read the instructions that come with them, here are some placement tips to help leverage the sensor's strengths:

1. Keep PIR sensors 3-5 metres away from heat sources like radiators, heating vents, and sunny windows. Motion sensors can trip upon detecting a swift change in heat, even that of a cloud passing quickly over direct sunlight in your living room.

Best spots for motion sensors

2. Place motion sensors at “choke-points”—areas where people have to walk through, like the stairwell or main hallway. That way, an intruder trips the sensor regardless of destination.

Checklist
No detours

Intruders usually go right for the master bedroom, so put a sensor near that room or other rooms with valuables, like the study.

3. Assess where intruders are most likely to enter and what path they would take. Most burglars enter the home through a front or back door, patio door, or garage door, so it’s advisable to place the sensors near those areas.

4. Find walls that an intruder would walk alongside, like a hallway or narrow pathway that leads to a room. Motion sensors work best when the intruder walks parallel to the sensor, not toward it.

Best spots for motion sensors

For example, in a hallway you tend to walk parallel to the walls, not directly toward them.

For more motion sensor placement information, read our article on How to Effectively Place Sensors in Your Home.

How to install a motion sensor

Indoor motion sensing camera
TP-Link Tapo Pan-Tilt camera

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With wireless motion sensors becoming standard, DIYers have it easier than ever when it comes to installation. If you know how to use a screwdriver, you can install a motion sensor. Correct installation gives you optimal coverage for motion detection and helps avoid false alarms.

1. Unbox your motion detector

Your motion sensor kit should come with some instructions and mounting hardware. If your device has separate batteries, now’s the time to put them in your motion sensor.

2. Decide on a location

You should consider the most effective sensor placement before mounting your motion detector:

  • Corners are an ideal location because you can position infrared sensors to cover the most area. Most motion sensor designs have angled edges with screw holes so they fit nicely into the corner of a room.
  • Mount your motion detector high on the wall to get the best coverage—but avoid putting it over a large piece of furniture, like a bookshelf or entertainment unit, because it will limit the passive infrared energy range.
  • Mount your motion sensor opposite a main entrance—this applies in every room or hallway where you place these sensors so they can detect intruders right away.

3. Mount the sensor

Passive infrared sensors are lightweight, so you won't have to worry about wall anchors or studs. A standard screwdriver should do the trick, but an electric screwdriver or drill can speed up the process.

Most motion detectors have a mounting bracket that pops off the main body of the device so you can screw it into the wall first, then clip the motion sensor back in. This also makes it easier for taking the motion detector off the wall during maintenance. Other infrared sensors may require a full disassembly for mounting.

4. Connect your sensor to your system

Follow the manufacturer's instructions to connect your motion sensor to your system. Most DIY systems walk you through this process, often using the main keypad or mobile app to set up and adjust your motion detectors.

If you have smart motion detectors, you can connect them to lights and other smart devices through a smart home hub like Amazon Echo or Google Nest so that a light turns on whenever there's motion. You can even use the smart hub's app to schedule motion alerts to your mobile devices when there's movement is during certain times of the day or night.

5. Adjust your motion detection settings

Most motion detectors have three main settings when you arm your system:

  • In instant mode, all motion triggers an alarm.
  • In entry delay mode, the sensor operates on a delay—even if it detects motion, you have roughly 30–60 seconds to disarm the system before an alarm.
  • Interior follow-up mode works on an entry delay, but only when door contact triggers first—though it sounds an instant alarm if it detects motion in the home without a door contact triggering.

6. Maintain your motion detector

Over time, dust and debris can gather on the screen of your motion sensor and interfere with the infrared energy, making it less effective at motion detection. Clean it at least once every couple of months with a dry or slightly damp microfiber cloth.

If you decide to paint a wall near your motion sensor, be sure to remove the device first. If you get any paint on a passive infrared motion sensor, you need to replace it.

Additional tips for installing motion sensors

Pet immune motion sensor

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Consider the size of your pets

Pet-immune motion sensors are only immune to pets when you use them correctly, and even then they can create false alarms under certain conditions.

Many pet immune sensors use ratings related to an animal's weight, but even small pets can trigger them with enough verticality. If your pet likes to practice their high jump, it can set off false alarms.

This is especially important if you have active sensors near a stairwell. At the bottom of the stairs, the sensor treats your pet like a mouse, but by the time your pet reaches the top, the sensor might see an elephant.

Overhangs decrease range

When installing LED motion sensor lights or cameras outside, keep in mind that installing them under an overhang (like a carport) can reduce their range.

Just like your field of vision decreases when you're wearing a hat with a brim or a visor, an overhang can block the motion detector light's 180-degree sensing angle, turning it into a 90-degree sensing angle.

Don’t block the infrared

Motion sensors are like flashlights sending out a beam of light but with motion-detecting infrared energy waves instead of light waves. Just like a light is brighter closer to the bulb, the infrared radiation is denser nearer to the device and it spreads out farther away.

A motion detector's waves can't penetrate through walls or other hard objects like furniture. When you set up your motion sensor, imagine it like a light on the wall. Anything that creates a shadow from that light's position can also block the motion sensor's ability to cover the shadowed area.

Motion sensing light switches aren’t all equal

When choosing motion sensing light switches for indoor use, remember that not all motion detection switches work the same.

  • An occupancy sensor turns on automatically when you enter a room and off again when you leave.
  • A vacancy sensor turns off the lights when a room is empty, but you have to turn it on.
  • Dimmer sensors are customizable for turning on lights at different levels of brightness.

Some brands have motion sensor light switches that come in all three options so you can choose the one that's right for you.

Other uses for motion sensors

Motion sensors aren’t just for home security. Many industrial fields use them on assembly lines to keep track of the number of products and to shut down dangerous equipment if a person gets too close.

Here are a few other uses for motion sensors

  • To open and close automatic doors
  • To turn on and off automatic water faucets and toilets
  • To turn on lights when a person enters a room
  • To control ATM displays
  • At automatic ticket gates
  • For some parking meters

FAQ

In addition to some nifty commercial applications, motion sensors are commonly used in home security systems to alert you (or your professional monitors) to someone's presence. 

  • An outdoor motion sensor can trigger a siren or alarm system to send unwanted visitors running. You can also place motion sensors near a swimming pool or tool shed to make sure your kids don't get into a dangerous situation.
  • A video doorbell camera with a built-in motion detector can tell you when a delivery person or visitor stops by.
  • An indoor camera with a motion sensor can start recording cute moments with your pets or alert you to your crib-climbing toddler. 
  • Some dash cams even include motion detectors to trigger recording when another car approaches your parked vehicle.

The sky's the limit! Just make sure you stick to self-monitored motion sensors if you're not using them to detect a break-in or other dangerous scenario. 

It depends on what you want to accomplish and the motion detector's viewing angle. Read our section on motion sensor placement for more information.

These are the common types of motion sensors:

  • Passive infrared sensor
  • Microwave sensor
  • Dual technology motion sensor
  • Area reflective sensor
  • Ultrasonic sensor
  • Vibration motion sensor
  • Contact sensor
  • Video motion sensor

 

Final word

Motion sensors aren’t just an additional feature of a security system—they are essential. Without sensors, there wouldn’t be a way to detect intruders.

Hopefully, our guide taught you the motion sensor’s role in your home’s security, the various technologies employed in motion detection, and how to properly install your sensors so they can do their job. For help researching your home security options, check out our article on the best DIY home security systems.


Disclaimer
Product prices and availability are accurate as of the date/time of publish and are subject to change. Any price and availability information displayed on the retailer’s website at the time of purchase will apply to the purchase of this product. SafeWise Australia utilises paid affiliate links.
Kasey Tross
Written by
Kasey Tross

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