When it comes to home security, infrared motion detectors are a must have. They allow you to sense motion within the covered area and respond by triggering (or not triggering) an alarm. Most motion detectors employ infrared technology. An infrared motion detector senses motion based on changes in the background heat signature. They’re almost always used to detect whether a person has moved into or out of a particular area. You might hear them referred to as passive infrared (PIR) or IR motion sensors.


How IR Motion Detectors Work

Everything that has a temperature above absolute zero emits detectable radiation

An infrared motion detector employs a pyroelectric sensor that is capable of detecting infrared radiation. Everything that has a temperature above absolute zero emits detectable radiation in the form of heat. Since absolute zero is -459.67 degrees Fahrenheit, that covers practically everything, including people and animals. This heat radiation is invisible to the human eye but can be detected by electronic devices such as IR detectors.

An IR detector works by detecting changes in the amount of infrared radiation in its field of vision, which means everything in front of the sensor. When a person passes in front of the sensor, the amount of radiation increases because the human’s body temperature is higher than the background temperature. The sensor detects this fluctuation, which is converted into a voltage change inside the IR detector. A person moving around within the sensor field also triggers a change. That’s because moving an object with respect to the background changes the radiation pattern and sets off the sensor.

IR sensors used in security systems are typically connected to a small relay. Usually the relay is wired in the form of a normally closed (NC) setup. That means it defaults to closed, but if motion is detected, the relay switches to open, which causes the alarm to go off. If you want to learn more of the science behind IR sensors, read this Wikipedia article.

Types of IR Sensors

IR sensors come in a variety of configurations. Most have an effective range of about 25-30 feet and a view width of 180 degrees. However, IR sensors with extended view fields of up to 360 degrees are also available. These types of IR detectors are usually ceiling mounted.

Another, less common type of IR detector is the active infrared detector (AIR). AIR detectors have two parts, a transmitter that emits infrared rays and a receiver that detects them. Anything that interrupts the pathway between the emitter and receiver triggers the detector.

Pets and Motion Detectors

Since anything that enters the field of vision will trigger a motion detector, false alarms caused by pets moving around can be a problem. Fortunately, Protect America infrared detectors can be set to ignore pets weighing up to 40 pounds. Some detectors are adjustable, allowing you to customize what should be ignored and what should trigger an alarm.


Choosing a Motion Detector

Since motion detectors have differing capabilities, it’s important to look for the features that are most important to you. These include:

  • Easy mounting
  • Wide field of vision
  • Ability to ignore pets
  • Long battery life

Get a Free Home Security Quote from Protect America

Motion detectors are an integral part of the monitored home security systems offered by Protect America. Our plans start at $19.99 per month, and you can even add on smart home automation as an option. If you’re interested in installing motion detectors in your home or business, contact us today for a free home security quote. We’d love to help you achieve 24/7 home protection.