The Beginner’s Guide to Motion Sensors

Written by | Updated October 9, 2019

A motion sensor (or motion detector) is the linchpin of your security system, because it’s the main device that 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 a sensor is tripped, a signal is sent to your security system’s control panel, which connects to your monitoring center, alerting you and the monitoring center to a potential threat in your home.

The following guide will answer all your questions about motion sensors: the different types, technology usedproper placement, and how to use and install them.

The Role of Motion Sensors in Your Home Security

illustration of a motion sensor's range of motion

The main purpose of motion detection is to sense an intruder and send an alert to your control panel, which alerts your monitoring center. Sensors work when you are not home, or when you tell the system you are not there. Some security systems can be programmed to record events via a security camera when motion is detected.

Motion sensors stand guard, ready to react to various situations, such as movement in your living room, windows or doors being opened or closed, or a broken window.

Motion sensors can:

  • Alert you in the event that your teen 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)

Detects body heat (infrared energy). Passive infrared sensors are the most widely used motion in home security systems. When your system is armed, your motion sensors are activated. Once the 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 sensors are tripped.

illustration of a person in a motion sensor's range
illustration of microwave motion sensing beam

MircoWave (MW)

Sends out microwave pulses and measures the reflection off a moving object. They cover a larger area than infrared sensors, but they are vulnerable to electrical interference and are more expensive.

Dual Technology Motion Sensors

Motion sensors can have combined features in an attempt to reduce false alarms. For example, a passive infrared (PIR) sensor could be combined with a microwave sensor. Since each operates in different areas of the spectrum, and one is passive and one is active, Dual Technology motion sensors are not as likely as other types to cause false alarms, because in order for the alarm to be triggered, both sensors have to be tripped. However, this does not mean that they never cause false alarms.

illustration of a dual technology motion sensor

Area Reflective Type

Emits infrared rays from an LED. Using the reflection of those rays, the sensor measures the distance to the person or object and detects if the object is within the designated area.

Ultrasonic

Measures the reflection off a moving object and sends out pulses of ultrasonic waves.

Vibration

These can be purchased or easily made at home. Detects vibration. A homemade vibration sensor uses a small mass on a lever, which is activated by a switch to an alarm when it vibrates. Homemade motion sensors can work, but they can also be unreliable.

Other Motion Sensor Features

Wireless Motion Sensors

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.

illustration of door sensor

Contact Motion Sensors (door/window)

Most contact motion sensors are passive infrared sensors. They trigger an alarm if the protected door or window is opened while the system is armed.

Pet Immune Motion Sensors

A passive infrared sensor can be set up to ignore animals up to a certain weight. A dual technology motion sensor is more resistant to false alarms caused by animals because it requires two sensors to be triggered in a manner determined by the manufacturer. They can be set up to ignore a large animal or multiple small animals without setting off a false alarm. Some pet immune motion sensors have a sensitivity level that can be adjusted for families with very active animals.

illustration of a pet-immune motion sensor

Video Motion Sensors

Combines video cameras with advanced signal processing. Some recordable motion sensors start recording when they sense motion. Cameras controlled by motion sensors can save you memory storage by not recording hundreds of hours of useless footage—they only capture the important stuff.

Best Practices for Mounting Sensors

illustration of motion sensor range
illustration of motion sensor range

If you choose a 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 or have you call a representative who will 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. They can also be triggered by animals, insects, and foliage.

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 your sensors. Also, consider the following motion sensor placement tips:

  1. Keep PIR sensors 10—15 feet away from heating vents, where the sunlight shines in, and radiators. If a motion sensor detects a swift change in heat, even that of a cloud passing quickly over direct sunlight shining into your living room, it could be tripped.
  2. Place motion sensors at “choke-points”—areas where people have to walk through, like the stairwell or main hallway. That way, an intruder will trip the sensor regardless of where they are headed. Intruders usually go right for the master bedroom, so put a sensor near that room or other rooms where you have valuables, like the study.
  3. Assess where intruders are most likely to enter, and what path they would take. Keep in mind that most motion sensors can detect between 50 and 80 feet. 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. For example, in a hallway you tend to walk parallel to the walls, not directly toward them.

How to Install a Motion Sensor

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 can give you optimal coverage for motion detection and help you 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 sensors are designed to 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 center, because it will limit the passive infrared energy range. Make sure your motion sensor is mounted opposite to the room or hallway’s main entrances so it will pick up on any intruders right away.

3. Mount the sensor

Passive infrared sensors are lightweight, so you won’t have to worry about drywall anchors or studs. A standard screwdriver should do the trick, but an electric screwdriver or drill can make the process go faster.

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 easy to take the motion detector off the wall later for 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. You can use your system’s app on your mobile device or use your system’s main keypad to choose the settings for your motion detectors.

If you have smart motion detectors, like the Samsung SmartThings motion sensor, you can connect it to lights and other smart devices through the SmartThings hub so that a light will turn on whenever the sensor detects motion. You can use the SmartThings app to set up motion alerts to your mobile devices when movement is detected during certain times of the day or night.

5. Set your motion detection settings

Most motion detectors have three main settings when your system is armed: instant mode, entry delay mode, or interior follow-up mode.

In instant mode, any motion the sensor detects will trigger an alarm. In entry delay mode, the sensor will operate on a delay—even if it detects motion, it will give you 30–60 seconds to disarm the system before sounding an alarm. Interior follow-up mode works like the entry delay but only if a door contact is triggered first. If it detects motion in the home without a door contact first being triggered, it will sound an instant alarm.

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’ll need to replace it.

Samsung SmartThings motion detector

Additional Tips for Installing Motion Sensors

Consider the Size of Your Pets

Pet immune motion sensors are only immune to pets when used correctly, and even then they can create false alarms under certain conditions. Many pet immune sensors are rated by an animal’s weight, but in reality, they’re based on height. If your pet likes to practice their high jump, it can set off false alarms.

This is especially important to remember if you have active sensors near a stairwell. At the bottom of the stairs, your pet may look like a mouse to the sensor, but by the time your pet reaches the top, the sensor will be seeing an elephant.

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 the farther away you get.

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

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 is reduced when you’re wearing a hat with a brim or a visor when a motion detector light’s 180-degree sensing angle is blocked by an overhang it becomes a 90-degree sensing angle.

Motion Sensing Light Switches Aren’t All the Same

When choosing motion sensing light switches for indoor use, remember that not all motion detection switches work the same. An occupancy sensor will turn on automatically when you enter a room and turn off again when you leave. A vacancy sensor will turn off when a room is empty, but you have to turn it on. Dimmer sensors can be set to turn on at different levels of brightness. Brands like Lutron 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 used for home security. In industrial fields, they are used 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 ways motion sensors are used:

  • 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

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 this motion sensor 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 best home security systems page.

Sources:

1. How Stuff Works, “How Burglar Alarms Work” 

2. Security Info Watch, “Making Sense of Motion Sensors” 

3. Digikey, “Panasonic Electric Works Design Manual”