How Motion Sensors Work

Posted by , , at 10:00 am

There is definitely some mystery surrounding motion sensors. They are a core element of most alarm systems, and it’s rare that I see an alarm system without at least one motion sensor. So, let’s dig into what they really do.

Motion sensors detect and report motion – in most cases when nobody is home. That’s why they are normally not “awake” when you arm your system for the night (see my recent post for a reminder on “Stay” vs. “Away” arming).  It’s usually not practical to puta sensor on every window, and you usually don’t need to, since you can use motion sensors and glass break detectors to get the protection you need more affordably. Plus, motion sensors have come a long way from the original models – much more reliable, and less prone to false alarms.

How do they work?

The early motion sensors were considered “active” devices, because they emitted energy (microwave or ultrasonic) to see what was happening around them. There are some still some microwave sensors being installed in commercial spaces. Today the most common motion sensor uses PassiveInfra-Red energy to detect heat given off by people (and animals!) – hence the name “PIR” given to the device. The smart detectors look for objects warmer than the normal background temperature, using a special lens to create “beams” of passive energy, and then look for motion: when the sensor detects a “warm” object moving across several beams within a specified time frame – that trips the alarm. If you want more of the science, here is a great link for the specifics.

Where do you use them?

The standard range is 30-35 feet, and the coverage area is shaped like a large water droplet, with the skinny part at the detector. The ideal spot for a motion sensor is in a high-traffic area that an intruder would cross if moving about in your home or business: think hallways, living rooms with big-screen TV, etc. The sensors work better when people move across the beams, as opposed to approaching the sensor directly. The beams project out and down, to pick up anyone trying to avoid detection by crawling. Do not point them at a heat source like a stove or fireplace, and avoid pointing at windows that get direct sun. And, don’t use them in a space that gets so hot that the sensor can’t tell an intruder from the ambient temperature – like a garage in a warm climate.

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! That means (going back to my previous blog post) that large dogs with the run of the house all day and night make it harder to use motion sensors – except for when you go on vacation, and board the critters.

There is a lot more I could say on the topic, but this is a good start. If you want more detail, you can check out the home security equipment video and podcasts at www.frontpointsecurity.com – or talk to one of our professional Security Consultants. They are trained to customize your alarm system appropriate to your home and lifestyle, or business – and all the reviews say they do a great job. This level of service is getting harder to find, but it’s a hallmark of the FrontPoint approach.  And when it comes to understanding motion sensors, give yourself a gold star; you’re ready for the next installment of Wireless Home Security 101!

 

Comments (49)

Post a Comment | View Comments
  1. Roland

    Hi,
    My image sensor is not recording images. Every time I go to the website (Alarm.com) to check images, it tells me no images have been found. What could be causing this? Thanks. :-)

    • Valerie Saponara

      Roland, there are a couple things that could be going on here, so when you have a chance please give our Support Team a call and they would be happy to walk you through figuring this out. Thank you!

  2. Angie

    Can a motion sensor in my garage detect someone outside looking in a window?

    • Gilbert Cho

      Hey Angie, the Motion Sensor will be able to detect movement outside of a window if it’s within range. However, be mindful that if the window in question receives direct sunlight, it may trigger the infrared sensors on the Motion Sensor.

  3. Lyn

    We have external motion sensor alarms on all our decks but every morning the sun triggers the alarm on one of them. Technicians have tried adjusting the beams but it still goes off. Is there a solution for this?

  4. Brian

    New user. My motion activated status has been on for 45 minutes and there is nothing moving in the room. I read that it should go back to idle after three minutes. Yesterday it took over an hour for it to go back to idle. Any ideas?

    • Gilbert Cho

      Hi Brian, hopefully I do a good job of explaining what’s going on here.

      What you read was correct – after the Motion Sensor has been activated, it should go back to idle after three minutes. However, if you’re looking at the sensor’s status on the app or website, there will have a bit of a delay (somewhere in the 45-60 min range) before it changes from activated to idle. This is because the Motion Sensor will only send what is called a “supervisory signal” every hour (as a way to conserve battery life) to let the Control Panel know its current state.

      So despite that you’re seeing it take a while for your Motion Sensor’s status to go back to its idle state, the actual physical Motion Sensor itself is going back to idle after only three minutes.

      I hope this cleared things up a bit! Please don’t hesitate to ask if you have further questions.

      • Brian

        Thanks!

  5. Alyssa Brown

    I am a Frontpoint customer with two motion sensors. My question is in relation to the notices I receive on my mobile device via alarm.com when a motion sensor is active or idle. I was wondering: let’s say I pass my staircase sensor- it will register as idle. How long before it will register as back to idle? And in that reset period (between being activated and back to idle), can another person walk past sensor and the sensor will or will not recognize it as a new motion and therefore as a notification on my mobile device (alarm.com)?

    • Gilbert Cho

      Great question, Alyssa!

      After initially activating your staircase sensor, it will stay in the activated state for about three minutes before returning to idle. During that three minute reset period, motion will not be reported as a notification on your mobile device.

      Thanks, and please let us know if you have any further questions!

  6. Alyssa Brown

    I am a Frontpoint customer with two motion sensors. My question is in relation to the notices I receive on my mobile device via alarm.com when a motion sensor is active or idle. I was wondering: let’s say I pass my staircase sensor- it will register as idle. How long before it will register as back to idle? And in that reset period (between being activated and back to idle), can another person walk past sensor and the sensor will or will not recognize it as a new motion and therefore as a notification on my mobile device (alarm.com)?

    • Gilbert Cho

      Great question, Alyssa!

      After initially activating your staircase sensor, it will stay in the activated state for about three minutes before returning to idle. During that three minute reset period, motion will not be reported as a notification on your mobile device.

      Thanks, and please let us know if you have any further questions!

  7. huss

    Hi there iv installed a bosch solutions 16+ alarm system with 3 wirless sensors. I programmed it correctly but for some reason the sensors dont trip the alarm and the guy I bought it off wont get back to me can I have some help with this please

    • Jamie Botzer

      I’m sorry about your situation, Huss. Unfortunately, we’re not going to be much help as we don’t have access to important information on the back-end. If you cannot contact the person who sold you the system, my suggestion is for you to try to reach someone else at Bosch Security. Good luck!

  8. huss

    Hi there iv installed a bosch solutions 16+ alarm system with 3 wirless sensors. I programmed it correctly but for some reason the sensors dont trip the alarm and the guy I bought it off wont get back to me can I have some help with this please

    • Jamie Botzer

      I’m sorry about your situation, Huss. Unfortunately, we’re not going to be much help as we don’t have access to important information on the back-end. If you cannot contact the person who sold you the system, my suggestion is for you to try to reach someone else at Bosch Security. Good luck!

  9. Alex

    We just installed ADT security system in our house with one motion detector that is supposed to cover the stairs that are leading up to the second floor. The motion detector does not go off all the time, when you crawl up on the stairs it does not go off. What could be wrong, the sensor itself or its position or something else? Thanks.

    • Jamie Botzer

      Hi Alex, you could be experiencing a variety of issues. It could be that the motion sensor is not equipped to cover the full stairs, or that it’s designed to detect a straight line coming out from the motion sensor, at a 90 degree angle. All of this would depend on the type of Motion Sensor you have. I suggest you contact ADT’s Customer Support directly, as they likely have more knowledge and understanding of the equipment within their system and should be able to help you troubleshoot. I hope this provides some assistance and good luck!

  10. Alex

    We just installed ADT security system in our house with one motion detector that is supposed to cover the stairs that are leading up to the second floor. The motion detector does not go off all the time, when you crawl up on the stairs it does not go off. What could be wrong, the sensor itself or its position or something else? Thanks.

  11. Chris

    I just added a motion in the garage to cover a newly install window with a window ac. This window does not get direct sun. And garage will get 85* tops in the summer if the ac ant on. Its a fully insulated garage… Should this be ok?

    • Peter M. Rogers

      Chris – we generally do not recommend a motion sensor in the garage, especially in climates where it gets hot in the summer. The motion sensor needs to detect a temperature of ~3.6 degrees F between the ambient background temperature and a large object in motion. The warmer it is in the garage, the harder it will be for the sensor to detect that intruder as having a different infrared “signature,” which is needed for the device to be triggered into an alarm condition. We think that a combination of door/window sensors and glassbreak sensors may be a better solution, and that is what we usually recommend. However in your case, since the garage is fully insulated, and has an AC unit, you may be okay. The best way to tell is by testing the sensor on a hot day when the garage is about as warm as it gets. And please feel free to call our Support Team if we can be of further assistance. Thanks for your excellent question.

  12. Susan

    Could you tell me what the minimum difference in temperature it would take for a motion sensor to detect an intruder? We will be leaving our house for a while with the A/C turned up to about 90 degrees. I am wondering if that is too warm for the motion sensor to work properly. Thank you for any information, Susan B.

    • Jamie Botzer

      Hi Susan! This is a great question, and I’m glad you asked it. It shouldn’t make a difference, but you may want to test it out while you’re still home in a small room (like a bathroom). That way, you’ll know if the warm temperature is going to set it off accidentally. If you’re having issues or have any other questions, please give our Customer Support team a call (877-602-5276) and they’ll be able to help you troubleshoot, as well as suggest some alternative solutions. Thanks!

  13. Ham

    Can I install motion detector in my backyard?

    • Peter M. Rogers

      Ham – not a good idea, unfortunately. We used to sell an outdoor motion sensor, but it was too prone to false alarms. For real outside protection, normally in a commercial setting, most systems use photo-electric beams to sense intruders. We do sell an outdoor camera that senses motion that will record a short clip, store it, and even send it to you – but that alone does not activate an alarm. Please call our Support team, and they can answer all your questions.

  14. Ham

    Can I install motion detector in my backyard?

  15. Jason Segree

    When will the GE Image sensor be offered by FrontPoint? Last I heard was that this was in BETA testing.

    https://www.alarm.com/productservices/imagesensor/image-sensor.aspx

    • Peter M. Rogers

      Jason – Thanks for your question. The image sensor is actually provided by Alarm.com, and not by GE Security – and is programmed to work extremely well with the next generation of alarm control panel from GE Security, which we expect to be released by GE later this year. We’ve been these product developments very closely! We are anxious to offer the image sensor once we are 100% comfortable that we can support it – and that it will meet our customers’ needs in the manner that all our other products do. Thanks again.

  16. Jason Segree

    When will the GE Image sensor be offered by FrontPoint? Last I heard was that this was in BETA testing.

    https://www.alarm.com/productservices/imagesensor/image-sensor.aspx

    • Peter M. Rogers

      Jason – Thanks for your question. The image sensor is actually provided by Alarm.com, and not by GE Security – and is programmed to work extremely well with the next generation of alarm control panel from GE Security, which we expect to be released by GE later this year. We’ve been these product developments very closely! We are anxious to offer the image sensor once we are 100% comfortable that we can support it – and that it will meet our customers’ needs in the manner that all our other products do. Thanks again.

  17. Julia

    Our house is a ranch, so it has a large footprint.
    If someone enters the house at the far end of the house, away from where the control panel is/alarm is, I’m concerned that the sound won’t be loud enough to scare them away. I read that in a review somewhere. Can you buy additional alarms or sirens, for both inside and outside of the house?
    Thanks

  18. Julia

    Our house is a ranch, so it has a large footprint.
    If someone enters the house at the far end of the house, away from where the control panel is/alarm is, I’m concerned that the sound won’t be loud enough to scare them away. I read that in a review somewhere. Can you buy additional alarms or sirens, for both inside and outside of the house?
    Thanks

  19. Julia

    My dog is 55 lbs. He has range of the house. I think you are saying that we can keep the system on Stay, which means he is here, and, when we go away for a weekend, with the dog, we can alarm the motion detectors. Is that true?
    Also, would it be possible to test whether he trips up the motion detector before a signal goes to the police department?

    • Peter M. Rogers

      Julia – Great question, and you are absolutely correct. Our motion sensor is “pet friendly” up to 40 pounds, which means the sensor will essentially ignore small pets (unless they are particularly acrobatic!). That means that with a small pet you should be able to arm the system in either “Stay” or Away” mode with small animals in the house – the difference being that in “Away” mode the motion sensors are active. However, in your case, with a larger dog who has the run of the house, you are going to use “Stay” mode when the dog is at large in the home, and “Away” mode when you AND the dog are out of the home together.

      As for testing the motion sensor, this is very easy – it’s called “walk testing,” and is often done when the system is being initially set up. Just call our Support team and they can talk you through this simple process.

  20. Julia

    My dog is 55 lbs. He has range of the house. I think you are saying that we can keep the system on Stay, which means he is here, and, when we go away for a weekend, with the dog, we can alarm the motion detectors. Is that true?
    Also, would it be possible to test whether he trips up the motion detector before a signal goes to the police department?

    • Peter M. Rogers

      Julia – Great question, and you are absolutely correct. Our motion sensor is “pet friendly” up to 40 pounds, which means the sensor will essentially ignore small pets (unless they are particularly acrobatic!). That means that with a small pet you should be able to arm the system in either “Stay” or Away” mode with small animals in the house – the difference being that in “Away” mode the motion sensors are active. However, in your case, with a larger dog who has the run of the house, you are going to use “Stay” mode when the dog is at large in the home, and “Away” mode when you AND the dog are out of the home together.

      As for testing the motion sensor, this is very easy – it’s called “walk testing,” and is often done when the system is being initially set up. Just call our Support team and they can talk you through this simple process.

  21. jessica fransisco

    with this motion sensor do this alarms the owner of the establishment? for example a thief would sneak in. would it alarm the owner that there is somebody sneaking? how about if i have some visitors and i installed this .would there be any difference? we’ll it’s a nice blog.

    • Peter M. Rogers

      Jessica – Thanks for your question. The way most systems work is that you may arm your system in either the “Stay” or “Away” mode. In the Stay mode the motion sensor will not create an alarm signal – that is the mode you use when arming the system when you are at home (like at night). The Away mode is used for when you are totally out of the house, and that is when the motion sensors will create an alarm signal. The way the motion sensor works is that if the alarm system is armed (Away) and the sensor is triggered, then the system sends an alarm signal to the monitoring center. The monitoring center will then try to reach you before dispatching the police. That is a standard process for most alarm systems, ours included. If the system is not armed, or is armed in Stay mjode, then the motion sensor still senses motion, but no alarm signal will be sent to the monitoring center. Hope that helps, and thanks again. If you would like more information, please call our Security Consultants and they will be happy to explain anything and everything to you.

  22. jessica fransisco

    with this motion sensor do this alarms the owner of the establishment? for example a thief would sneak in. would it alarm the owner that there is somebody sneaking? how about if i have some visitors and i installed this .would there be any difference? we’ll it’s a nice blog.

    • Peter M. Rogers

      Jessica – Thanks for your question. The way most systems work is that you may arm your system in either the “Stay” or “Away” mode. In the Stay mode the motion sensor will not create an alarm signal – that is the mode you use when arming the system when you are at home (like at night). The Away mode is used for when you are totally out of the house, and that is when the motion sensors will create an alarm signal. The way the motion sensor works is that if the alarm system is armed (Away) and the sensor is triggered, then the system sends an alarm signal to the monitoring center. The monitoring center will then try to reach you before dispatching the police. That is a standard process for most alarm systems, ours included. If the system is not armed, or is armed in Stay mjode, then the motion sensor still senses motion, but no alarm signal will be sent to the monitoring center. Hope that helps, and thanks again. If you would like more information, please call our Security Consultants and they will be happy to explain anything and everything to you.

  23. Tibor

    Question. I want to install your system but my only hesitation is that I have exactly what you refer to; an acrobatic Siamese cat. However, he is getting on in age and not as active as before but still highly agile. If I’m out he will mostly sleep as the other cat I have is not very playful. But, you never know, the Siamese can jump high and get up into high places. My question is: If the motion sensor detects heat and movement why is having an agile cat a problem? He is only about 11.5 lbs so will not trip the heat sensor.

    • Peter M. Rogers

      Tibor – Great question, and you would be surprised how often it comes up. Most cats and small dogs weigh under 40 lb., which is the weight “cutoff” for our pet-friendly motion sensor. And you are right: the motion sensor uses a combination of passive infrared sensing and motion analytics to generate an activation. The problam is that even a smaller cat that is vary active can generate a larger “image” that can trigger the sensor. It does not happen every time, but it can happen.

      One option is to restrict where the active cat can go, but many people do not want to do that. Another is to use fewer motion sensors, and instead rely on a combination of door/window sensors and glassbreak sensors – all of which are active either in the “stay” or “away” armed modes. Our Security Consultants can easily talk you through the system design aspects of this option. Thanks for your excellent question!

  24. Tibor

    Question. I want to install your system but my only hesitation is that I have exactly what you refer to; an acrobatic Siamese cat. However, he is getting on in age and not as active as before but still highly agile. If I’m out he will mostly sleep as the other cat I have is not very playful. But, you never know, the Siamese can jump high and get up into high places. My question is: If the motion sensor detects heat and movement why is having an agile cat a problem? He is only about 11.5 lbs so will not trip the heat sensor.

    • Peter M. Rogers

      Tibor – Great question, and you would be surprised how often it comes up. Most cats and small dogs weigh under 40 lb., which is the weight “cutoff” for our pet-friendly motion sensor. And you are right: the motion sensor uses a combination of passive infrared sensing and motion analytics to generate an activation. The problam is that even a smaller cat that is vary active can generate a larger “image” that can trigger the sensor. It does not happen every time, but it can happen.

      One option is to restrict where the active cat can go, but many people do not want to do that. Another is to use fewer motion sensors, and instead rely on a combination of door/window sensors and glassbreak sensors – all of which are active either in the “stay” or “away” armed modes. Our Security Consultants can easily talk you through the system design aspects of this option. Thanks for your excellent question!

  25. Alan

    Great motion sensor overview Peter. Thanks!

  26. Alan

    Great motion sensor overview Peter. Thanks!

  27. Jamie Botzer

    Hi Susan! This is a great question, and I’m glad you asked it. It shouldn’t make a difference, but you may want to test it out while you’re still home in a small room (like a bathroom). That way, you’ll know if the warm temperature is going to set it off accidentally. If you’re having issues or have any other questions, please give our Customer Support team a call (877-602-5276) and they’ll be able to help you troubleshoot, as well as suggest some alternative solutions. Thanks!

Leave a Comment