In our first post covering Home Security 101, we discussed wireless door and window sensors. Now let’s cover the second piece of alarm equipment crucial to home alarm technology and systems: the wireless motion sensor. Motion sensors detect and report motion. When incorporated into your home security system, motion sensors can help identify when someone is moving around inside your home.
As with other home security devices, the trend has been moving toward wireless alarm technology for years. That means no drilling, no running wires, and a faster (and cleaner) installation process. It also means that these sensors are easier to troubleshoot, to adjust, and even to move with you if you are fortunate enough to have a DIY alarm system.
I will explain how a motion sensor works and why they are an important component of just about any home alarm system. I’ll also explain the different types and optimal motion sensor placement.
Types of Motion Sensors
Motion sensors can detect activity—in most cases when nobody is home. That’s why they are normally not “awake” when you arm your system for the night. Motion sensors are an important part of a home alarm system because it’s not always practical to put a door or window sensor on every entry point. Motion detectors and glass break detectors can help you get the protection you need more affordably.
There are several different types of motion detectors that use different technology to function:
- Passive infrared (PIR)
- Area reflective
Passive Infrared (PIR) Motion Sensors
PIR motion sensors are among the most common type of motion detectors used today in home security systems, including Frontpoint’s. When armed, these devices detect heat given off by people and animals. They look for objects warmer than the normal background temperature using a special lens to create beams of passive energy. They also look for motion. When the PIR motion sensor detects a warm object in motion across several infrared beams within a specified time from, it trips the alarm.
Microwave Motion Sensors
Microwave motion sensors use microwaves to “see” what is happening around them. They send out pulses of microwaves, which bounce off of objects and reflect back to the sensor. If an object is moving, the measurement between it and the sensor will change, which trips the alarm. Many of the early motion detection devices used microwave technology, and there are still some microwave sensors being installed in commercial spaces today. Though they cover a larger area than PIR devices, microwave motion sensors are typically more expensive and are subject to interference from electrical pulses.
Ultrasonic Motion Sensors
Similar to microwave motion sensors, ultrasonic motion sensors send out pulses of ultrasonic waves, which bounce off of objects and reflect back to the sensor. The device measures the distance between it and objects, and if the measurement changes it trips the alarm. Ultrasonic motion sensors were more popular when motion detectors were first invented, but aren’t widely used today.
Multi-technology Motion Sensors
Also called dual technology motion sensors, multi-technology motion detectors use aspects of more than one type of device. By combining “passive” and “active” technologies, like PIR and microwave, for example, multi-technology motion sensors reduce the likelihood of false alarms.
Other Motion Detectors
Two types of motion sensors that are used less frequently are area reflective motion sensors and vibration motion sensors.
Area reflective motion sensors use a light emitting diode (LED) to send out infrared rays. Just like microwave and ultrasonic technology, the sensor measures the distance of an object and if the distance changes, the alarm goes off.
A vibration motion sensor uses a device—often an accelerometer—to measure vibrations in a structure. If the vibration exceeds a certain amount, an alarm is sounded. Crude vibration motion sensors can be made at home, but we do not recommend this—homemade sensors are often less reliable and can cause false alarms.
Motion Sensor Placement
The standard range for PIR motion sensors is about 30 feet. The coverage area is shaped like a teardrop, with the skinny part at the detector. If placed strategically, motion sensors can maximize the security coverage in your home or business.
The ideal spot to place a motion detector is in a high-traffic area that an intruder would cross if moving about in your home. To maximize “catch” performance, beams project down and out to pick up anyone trying to avoid detection by crawling.
Some examples of ideal motion sensor placement include:
- Near major home entry points, like the front door, back door or patio door.
- A hallway that a person must walk through to access your home
- A living room or waiting room with a big-screen TV
- Near a bedroom door
- In the corner of a room with multiple entry points
- In a garage
- In a basement
You should avoid placing a motion sensor near the following places, as they can trigger false alarms:
- Facing a window that gets direct sun
- Facing an uncovered, street-level window where cars or people are moving directly outside
- Near an HVAC vent or a drafty place
- Facing a radiator, fireplace, stove or other heat source
- Inside a hot garage
You might be asking yourself, “How many motion sensors do I need?” The answer depends on your space. Motion sensors work better when intruders move across the beams, as opposed to approaching the sensor directly. Depending on the layout of your home, you may need to install sensors across from each other so there’s no chance an intruder wouldn’t cross the beams.
Indoor vs. Outdoor Placement
Since a home security system is designed to protect the valuables and people inside your home, you’ll likely put most of your motion sensors and other alarm devices inside your space. However, there are also merits to placing a few sensors outside. If you live in an area where people aren’t constantly walking by, like the suburbs, it might be beneficial to place a motion sensor on a deck, patio, porch or even a long driveway. Though may not be practical to put a sensor outdoors, you may want to consider using a motion-activated security camera instead, which records clips when it detects movement.
Downsides of Motion Sensors
Though motion sensors can be a useful part of a home alarm system, intruders may be able to fool them. By knowing ways someone can do this ahead of time, you’re better able to protect your home.
Some ways to avoid tripping a motion sensor include:
- Moving extremely slowly
- Walking directly underneath a detector
- Walking and hiding behind large pieces of furniture
- Crawling or crouching to a pet’s height
- Covering a motion sensor with a piece of paper, foil or fabric
Many modern motion detectors are designed to withstand these evasion tactics. For example, the motion sensors Frontpoint uses project beams down and out to detect someone who is crawling. You can also prevent someone from fooling your home security motion sensors by placing them in the following areas:
- Hiding amongst decorations, like on a mantle or bookshelf
- Behind your valuables, like a TV or computer
- On the ceiling
To maximize the protection of your home, you should also consider using multiple types of devices. By using window sensors, door sensors and glass break sensors with motion sensors, you’re more likely to catch an intruder.
Motion Sensors and Pets
Today’s sensors are usually “pet-friendly” up to 40 pounds, which means they ignore cats and small dogs—unless your Siamese is downright acrobatic! However, this means that large dogs with the run of the house all day and night make it harder to use motion sensors. The exception, of course, is when you go on vacation and board your critters.
Until Next Time
It’s true that every home alarm system I’ve seen over the past 25 years has at least one motion sensor. They work, they are reliable, and they should not cost a lot. That’s why they are one of the key components when designing a complete home security system, along with window and door sensors. In our next Home Security 101 post, we’ll be talking about glass break sensors, which can add another layer of protection to your home.