How Do Motion Sensors Work?

By September 7, 2021 No Comments
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When it comes to protecting the people you love and the property you live on, there are few technologies as efficient as motion-sensing systems. Motion detectors trigger lights or alarms and are excellent tools for ensuring the safety and security of your home. Burglars are often deterred by the presence of motion sensors. Read on to learn more about how a motion sensor works and how it can help protect your home. 

What Are Motion Sensors & How Do Motion Detectors Work?

Not all motion sensors are the same. In fact, there are two different types of sensors: active sensors and passive sensors. Active sensors send energy into an environment to detect a change in this energy. The energy sent can come in the form of UV waves (light), microwaves, or sound waves. One example of an active sensor is found in automatic door openers, like in grocery stores. There’s a box by the door that sends out microwaves that are reflected back, creating a field of energy. When someone steps into the space, the energy is interrupted, and the door opens. 

There are also passive motion sensors that detect energy rather than create it. Most passive motion sensors detect infrared energy. Motion sensors that are part of a home security system are passive sensor systems and use Passive Infrared (PIR). To detect an intruder, a sensor needs to be sensitive to the approximate 93ºF temperature of a human body. Humans radiate infrared energy, with a wavelength that ranges from 9 and 10 micrometers, so effective motion sensors are sensitive to between 8 and 12 micrometers. 

Types of Motion Sensors

There are several types of motion sensors used in homes—though most are Passive Infrared. These are the most common and how they work: 

Passive Infrared

The most common type of home motion sensor is the Passive Infrared (PIR) sensor. A PIR motion sensor lens detects infrared light but only quick or large changes in the field of view. The sensors usually don’t pick up on a person standing still directly in front of the lens because that’s not a change in energy levels. But if a person moves in front of the sensor, it’ll detect that because of the change in energy. In a sense, PIR creates a grid of protection wherever it reaches. 


A little bit less common of a sensor for home security is the microwave sensor. A microwave sensor sends out microwave pulses that reflect off of objects in the area. The reflected microwaves help the sensors determine if something is in the area. These sensors are common in grocery store doors but not so much in home security systems. This is because these sensors are often more expensive than PIR sensors, and they’re more vulnerable to electromagnetic interference. 

Dual Technology

Some home security sensors use both PIR and microwave technology. These sensors were created to reduce false alarms. For a dual technology sensor alarm to sound, both the infrared and microwave sensor has to pick up on a disturbance. These sensors are less likely to trip a false alarm, but it doesn’t eliminate the possibility of a false alarm. 

The Role of Motion Sensors in Home Security

Common home security sensor components are door sensors, window sensors, and glass break sensors. When your home security system is armed, door and window sensors sound an alarm when the door or window is opened, alerting you to a potential security threat. A fully protected home will include sensors in several different places since motion sensors only have a range of about 10–15 feet. 

Door Sensors

Door sensors are some of the most common because sensors should be placed where intruders are likely to try and enter the house. Door sensors often use a magnet to determine if the door has been opened. These sensors can sound an alarm if the door is opened once the system is alarmed. Often this alarm will scare burglars. Door sensors are also hard to tamper with—burglars would likely trip the alarm even if they had the right materials. Many people install door sensors on each door in their home to cover all the major entrances. 

Windows Sensors

Window sensors work very much the same way as a door sensors. They also use magnetic field technology to alert you if the window is opened. However, sometimes you might like your windows open a crack, even at night. To counter this challenge, many people install two sensors that must be triggered for an alarm. The second sensor can be higher up on the window frame, so you can crack the window a little without setting off your own alarm. 

Glass Break Sensors

There are actually two kinds of glass break sensors: acoustic and shock. But both sensors are designed to alert you if the glass shatters in your home. An acoustic sensor works by “hearing” the soundwaves of a shattering window. Because it works off of sound, one acoustic sensor can cover multiple windows in the same room. A shock sensor “feels” the disruptions caused by breaking glass. These sensors rely on touching the disturbance, so they have to be installed onto the window they’re protecting. 

How To Choose The Right Motion Sensor For Your Home

There are many things to consider when choosing motion sensors for your home. These are some of the most important things to consider: 

  • How many sensors do you need? Most homes need more than one sensor to adequately protect your house. 
  • Where are your major access routes? Doors, windows, patios, garages, and other access points are the most likely routes a burglar will take. You’ll want to make sure these routes are protected. 
  • Do you have pets? Pets can sometimes set off motion sensors, but not all motion sensors are prone to this. Most PIR sensors can ignore pets up to a certain weight. For larger pets, a dual technology sensor can help. These sensors have to be triggered in two ways to go off, and pets don’t often trigger it. 
  • Do you have any overhangs? Overhangs, like carports, can reduce the range of your sensors. When installing sensors outside, you’ll want to avoid placing them under an overhang. 
  • Do you have children? If you have young children, you’ll want to explain the system to them. If your children are home alone, it might be good to teach them how to enter the house with the code to avoid setting off the alarm while still keeping them safe. 

Motion Sensors From SafeStreets

SafeStreets’ motion sensors are designed to help keep your home protected. Our security experts will help you through the entire process of choosing motion sensors, installing them, and getting your home security system up and running. You won’t have to worry about picking out the right type of sensors on your own, because we can help you find the right ones based on your unique situation. We’ll also help you figure out how many you need and where they’ll need to be installed to be most effective. We’ll even show you how to work your sensors. We make it easy for you to keep your home safe. Get your free quote to get started with motion sensors.

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