Motion Sensors Buying Guide

A motion sensor is essentially the backbone of your home security system because it is what detects any movement and alerts you when an intruder is around or in your home. It also has many other valuable uses as we'll discuss in this guide. Motion detectors employ various technologies to sense movement in any given area. Once that sensor is tripped, you will be notified of any potential danger in your residence. This guide is designed to help you better understand how motion sensors work, what the different types are, and how to properly install and use them.

Why are Motion Sensors So Important to Have?

Motion sensors are essential because they work to keep your home safe when you're home and when you're not. Some security systems can even be setup to record things on a security camera, allowing you to retrieve live footage if needed in the event of a crime scene.

The main purpose of motion detectors is that they sense potential thieves and intruders and alerts you of them. They can sense movement anywhere such as in front or by your door, the windows, or in your living room, for example. Keep in mind that motion detectors are not just used for security reasons. They also have plenty of other useful purposes! In addition to protecting your home from intruders, motion sensors can also do the following:

  • Let you know if your child or pet has entered an area of the home where they shouldn’t be
  • Notify you if your teen is not home by a certain time
  • Lower energy costs by turning off lights that are accidentally left on after a certain amount of time has passed
  • Serve as a doorbell to inform you that someone is in front of your door
  • Open and close automatic sliding doors
  • Turn on lights when someone comes into a room
  • Control automatic water faucets
  • Open and close garage entrance gates in gated complexes

What are the Different Types of Motion Sensors?

Not all motion sensors are made equally. In fact, there are so many different types, it's important to familiarize yourself with them before committing to one, depending on your needs. Below are some popular types of motion detectors:

Active Sensors

Active sensors rely on methods like radar waves or infrared energy to sense changes in a given spot. They can sense even minor movements. The most common active sensors are:


This type is the most commonly used type in lighting and emits sound waves higher than a human can hear.


Microwave sensors are extremely sensitive and are mostly used in security systems. They are not always calibrated accurately and are thus more prone to false alarms compared to other types.


This type of sensor emits radio waves and are often used in commercial areas that require a high level of security. Tomographic sensors can cover larger areas compared to ultrasonic and microwave sensors.

Passive Infrared Sensors

Compared to active sensors, passive infrared sensors (PIR) are a lot more energy efficient. They detect changes in heat given off by any warm-blooded creatures and the sun. PIR motion sensors have a thin layer of pyroelectric material and two slots, which is what reacts to the IR radiation. The sensor essentially stays idle in the area until a person or animal walks through there, triggering a change of temperature between the two slots and activating the sensor. PIR sensors can be programmed to only activate at certain heat levels, so that the minor fluctuations in temperature won’t cause the lights to keep turning on. Since PIR sensors are limited to line-of-sight, it's important that you place it somewhere where it won’t be blocked by anything like shelves.

Dual Technology Sensors

Dual technology motion sensors are ideal for bigger settings where using just one technology is not enough. Such settings include offices, classrooms, and other spaces with high ceilings, for example. These sensors combine ultrasonic and PIR sensing technology so that lights turn on when both are activated, to ensure that lights stay on while that given space is being occupied.

Occupancy vs. Vacancy Sensors

Occupancy sensors are designed to automatically turn on lights when they detect movement, and turn off lights after a programmed amount of time has passed with no movement. These light sensors come in handy in high-traffic areas like bathrooms, classrooms, and offices. On the other hand, vacancy sensors will turn off any lights in a room with no movement. The main difference between occupancy and vacancy sensors is that vacancy sensors require that you manually turn on the light when you enter the room. This type of sensor is better suited for spaces that have plenty of natural light during the day, such as offices and conference rooms.

Area Reflective Sensors

For area reflective sensors, LED lights send out infrared rays to measure the distance between the sensor and its surroundings. The sensor will be tripped if it detects any rapid movement.

Vibration Sensors

These sensors sense vibration in the vicinity of an area, and can be readily purchased or easily made from the comfort of your own home! Homemade motion sensors employ a small mass on a lever. Any vibrations will activate a switch to an alarm. They can work but may not always be 100% reliable.

Motion Sensor Features

Just like anything else, depending on your lifestyle, some features may be more important than others when looking for a home security camera. To get started, let's consider a few popular important features when comparing options:


Most motion sensors today are wireless, which means that they do not require any drilling and communicate with other security system parts wirelessly. They are easy to install and operate.

Contact Sensitive

Contact motion sensors trigger an alarm if a protected window or door is opened while the system is alarmed. You’ll be notified right away if someone is breaking in.

Pet Immune

A passive infrared sensor can be calibrated to ignore animals up to a certain weight, so that if they are passing an area, an alarm won't be set off. However, if a person that is clearly heavier than an animal enters when they shouldn't, you'll be notified. Depending on the sensor you get, you may be able to adjust the sensitivity level depending on your family’s lifestyle.

Video Capability

Some motion sensors are compatible with security systems with video cameras and advanced signal processing. This allows for recording to begin only when there is motion in a given area, ensuring that you're not recording hours of useless footage and eating up memory storage. Video capability comes in handy especially when you may need live footage of any criminal activity in your home or office.

Tips for Installing Motion Sensors

Before installing any motion sensors, it’s important to read through the instructions and familiarize yourself with the device. This will not only save you time during the installation process, but also reduce the chances for error.

Motion detectors are not error-proof. There are definitely chances you'll get a false alarm here and there, and they are usually caused by user error, poor installation, lightning, bad equipment, power surges, or electrical failures, for example. Depending on the type of motion sensor, it can also be triggered by blowing foliage or animals. This doesn’t mean that there aren’t methods to increase the effectiveness of your motion detectors though. False alarms can’t be eliminated completely but can definitely be prevented.

Below are some tips for installing your motion sensors:

  • Strategically install motion sensors in areas where people have to walk through like a main hallway. This way, an intruder trying to get in will trip the sensor regardless of where they come from or where they are headed. The master bedroom is a popular spot for intruders to enter, so you may want to consider placing a sensor near that room or other rooms where you store your valuables.
  • Keep your PIR sensors 10-15 feet away from heating vents or areas where the sunlight may shine in. The motion sensor light may give a false alarm if it senses a drastic change in temperature.
  • Remember that most motion sensors cover between 50-80 feet. You’ll want to install your sensor lights accordingly, in paths intruders are likely to take/areas where they are most likely to enter.


Motion sensors are crucial for home security — without them, we wouldn’t be able to detect intruders. They are also used in many other settings and for a plethora of purposes. Taking the time to strategically install one or several in your home or office will not only provide you with a peace of mind when it comes to safety, it can also help save on energy costs.