Greg B. wrote in asking about the benefit of window sensors for a monitored security system that he is planning for his new home in Carmel Valley. In my opinion, the benefit is little or none.

In a modern home with modern double pane windows, it is virtually impossible to open those closed and locked windows from the outside. A window sensor can ONLY detect a window going from closed to open, so if you can not open it from the outside there is not anything to detect. Most window break-ins occur through open windows. If your window is open even an inch, you would have to bypass that sensor before you could arm your system, so entry through an open window would not set off the alarm. The other way that a burglar would enter through a window, which is much more rare, is to break or cut the glass. If the burglar then enters through the hole that is created, the window frame is not moved and the window sensor and magnet are not separated, so the alarm is not tripped.

So long as you have at least one motion detector as part of your security alarm system, an intruder entering through a window will trip the alarm when they pass through the area covered by the motion detector. Modern motion detectors are “pet immune”, so even people with animals roaming in their home can effectively use motion detection to secure their property. Electronic security systems are designed to instantly go into alarm if the motion detector picks up human movement in the home and an entry door was not open first, so their is no delay in the siren sounding and scaring the intruder out of the property.

The only practical use  for window sensors are for windows that you like to leave open a few inches to allow fresh air to enter your home. In that instance, you can get a “vented window” sensor where two magnets are installed. One magnet lines up with the sensor when the window is closed, and the second magnet lines up with the window open a few inches. Now you can arm your system with the window open to the vented position, and if any of those open windows are opened further by a would be intruder, the system instantly goes into alarm. This can be done on just two or three windows in the house, which is very affordable. To put sensors on all of your windows is very costly, and can make for a cumbersome system that is difficult to use. Typically when a system is difficult to use, people do not get in the habit of arming their system and all of that money they spent on window sensors is a complete waste!

Keep it simple and create the habit of arming your system, and your home will be secure.

53 responses to “Motion Detection vs. Window Sensors”

  1. Anon says:

    Wow. No benefit to window sensors!? Ever here of a crowbar? And even if they don’t break open a window…having window sensors lets you make sure your windows are shut before you leave home. I would say there a pretty valuable part of the system. As far as expensive…most wired window sensors cost about $2-$5…wireless are a little more pricey…but still that’s pretty cheap in my opinion.

    • alarm2000 says:

      I don’t know what your opinion is based on. Many people form opinions on subjects that they have little or no factual information to base them on. My opinion is based on real crime statistics and personal experience of securing homes AFTER they are broken in to and learning how the intruder gained entry in to their home. Ultimately it is my job to give my customers peace of mind. If putting sensors on all of their windows achieves that, then I am more than happy to do that for them. You are correct that if a home is wired (most are not), the cost is not substantial, however wireless sensors add about $75 each to the cost of a system. With 20 windows that is $1,500, which I don’t think is “cheap”. Thanks for your comments. I am glad to see that people are checking out the site. Best wishes, Keith

      • Private says:

        it would make sense that a thief would look for an open window downstairs and no cars on the drive, when you can grantee they have gone out, there is a good chance that they don’t have a burglar alarm as if they did then the window sensor would prevent them from setting it. Then s/he could just climb in the window, if the alarm does start going off then they would know that no one is home and would have about 5 / 10 mins of robbing before a neighbour gets annoyed at the sound and looks out the window. most people wouldn’t bother to call the cops either. this is simple logic even a dumbass thief could figure it out.

    • alarm2000 says:

      First of all, if a window is open as you describe in your comment, then a window sensor would prove useless, since that zone would have to be bypassed in order to arm the system. Second, statistically the most likely intruder is a teenager looking for drug money. He or she is a bad kid since they are stealing from their neighbors, but they are still a kid, and very scared to be in a stranger’s home. I doubt that they will linger for 5-10 minutes with a 100+ dB siren blaring. They will likely leave the premises as quickly as possible and run away, which is exactly what we are hoping to accomplish. Your assumption that a “dumbass thief” can figure anything out is being very generous to the dumbass. Actual crime statistics don’t support your assumption. Thanks for your comments.

  2. The Thinker says:

    My thought is
    1. deterence first (signs, stickers and fake cameras)
    2. Reminders or window, door and or garage door sensors (to remind you to close each one).
    3. Sensors and motion (directly above) each back and side entry. One motion running all the time in the basement is a hassil for us late night people.
    4. Cameras, Infra Red so you can see them!
    5. Dog
    6. 1200 volts around each entry way
    7. Dog and gun

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  4. Cy says:

    I wounder. If I have a motion detector pointing at the windows. Is there any sane reason to put additional sensors on the windows? Even if left open. Entering the window would still put of the alarm. no?

    • Keith says:

      The only good reason would be if you like to leave the window open just a few inches while you are sleeping. Then a “vented” window sensor with two magnets can be beneficial. Other than that, I agree that motion is the way to go. Thanks for your comment.

    • IA says:

      Some alarm systems allow you to turn on only the access sensors while leaving the motion sensors off. That’s usually called “home mode” and that is very useful when you want the alarm enabled while still at home, such as every night when going to bed.

  5. tony says:

    i am sorry but if you setup a number of systems you know that there is a stay and away setting for alarms.

    When you are home you don’t want motion sensors active because it means a trip to the bathroom or kitchen means you need to turn your system off and if someone is watching and knows your home thats when they break in.

    In the away setting you have the door, windows and motion sensors on this prevents someone from cutting a hole in your wall and walking around with no motion detector to catch them.

    The problem is security system manufacturers know that if they sell wireless sensors that don’t need the battery replaced for 7 to 10 years then a customer only needs to buy them once in the time they live in the home. They probably are only worth $15 each even with a profit for the manufacturer but they charge $30 – $70 because they know you are only buying it once.

    The way around this is that many new wireless systems allow 1 wired loop and this can be used for wired door and window sensors that are used in the stay setting. If a window or door is too hard to wire you can add a wireless zone to the wired zone for the stay option and use a wireless sensor in that location.

    But there are systems that mix both wired and wireless and give you more then one zone for the wired… if you own one of them you can add other devices that are within the wired area such as a glass break or other detector.

    NOT SECURING every entry point means you can not have a secure stay setting .. and really isn’t that the most important time to secure your home.. when you are home and sleeping .. rather then when you are at work and if something gets stolen your insurance will cover it.

    Secure every entry and don’t depend on spending $300 for a system with 3 sensors .. 2 door and a motion detector unless you are living in an apartment with only one door and one window.

    • Ryan says:

      you are 100 % correct.. every window in a home should be completed w/ motion sensors as a backup or cross zone verification is the only proper way t protect my family when i put my head on my pillow!

  6. tony says:

    oh i should also add that

    most windows can be easily opened by sliding a slim jim .. thin piece of metal between the windows and forcing the lock open.

    this is not true for hopper windows found in basements

    and also most doors can be picked within 30 seconds so no lock is going to help if it has a key on the outside of the door.

    so your assumption that only open windows get broken into is really wrong there

    • Robert says:

      Not if you bought decent locks. Call out a locksmith and see how long it takes with bump proof locks. They all switch to drills and destroy the lock instead and it takes a hell of a lot longer than 30 seconds.

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  8. Champak says:

    Every security system is just to add some delay. If you use cheap device or lock a burglar can break it in less time. But if you use a better one it will take some more time for him to break. That way burglar can break open a vault also if he gets sufficient time. So, there is nothing called best security device. Home alarm system requires some sort of habit or discipline to get the desired result. If you keep it disarmed always it is not going to help you anyway. However, with proper alarm device and habit you can make your home much secure than without having an alarm system. BTW, going for alarm system which depends on telephone line or internet has no use as burglars know where is the telephone line or cable line in your home and they will cut that first. Best option is to go for alarm system which communicates with its monitoring station through wireless communication (CDMA or GSM).

  9. Keith says:

    Hi Champak,

    Thanks for your input. It is true that if you do not get in the habit of arming your system, it is not going to prevent a burglary. That is why I always try to keep my systems as simple in nature as possible. The more complicated the system, the less likely that the homeowner will typically develop the habit of using it.

    In terms of your comment on burglars knowing where the phone and cable lines are and will cut it first, I have to disagree. You are giving these folks way too much credit. Home burglaries are primarily carried out by teenagers, not sophisticated burglars unless you have hundreds of thousands of dollars worth of valuables in your home that would attract a pro. I have installed systems for hundreds of homeowners who are active or retired law enforcement, and I ask them if they have ever heard of burglars disabling phones before stealing from a home, and the answer has always been “NEVER”.

    That said, we do install CDMA or GSM modules for many of our customers who either do not have a home phone line, or who like yourself worry about the vulnerability and sleep better with this type of communication between their system and the central station. Ultimately, it is all about having peace of mind, and we are pleased to help people have theirs. Thanks again for the comments!!

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  14. PIR motion sensors will be the thing of the past with the advent of Tomographic Motion Detection. Here is a nice article on TMD that I found.

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  17. rob says:

    How ignorant tof think just a motion setting off an alarm will make the bad guy run. 91% of break ins go straight for the master bedroom (gold mine in any home). Takes just a few minutes. If a burglar alarm is activated when I’m already “pot committed”, I’m taking something. Get your windows done. Get some glass break detection. Get early detection and make that “teenager”make their secession while their get are still on the grass. Keith…. do more research before you provide a false sense of security.

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  24. Becca says:

    I have a question. We just had a wireless system installed by ADT. ALL entry points have been wired, as well as motion detectors setup. I know when we are home, put it in stay (so our sleep walker kids don’t trigger the sensors). And when we leave, we set it to away. The alarms I know will sound when the window/doors are opened. What about if the window was broken , when we were sleeping and it’s in stay mode, and that is how entry is gained?? They technically did not “open” the window or the sliding door. So how would this protect my family and I?

  25. Robert says:

    Instead of the two magnets to leave windows open for ventilation how about longer, 7″ or so, magnets that allow a window to be opened or closed while the system is armed? I remember seeing something about these in the past, but I cannot locate them now. Do you know if they still exist?

  26. swichter says:

    I had a break in and the idiot threw a giant and I mean huge cement block for plumbing through a window that had a sensor on it. It was the interior motion detectors in the rooms that scared him off. I don’t think he, yes, I said he, took anything.

  27. Conan says:

    Well it doesn’t look like this post is watched anymore by the original poster but this is a question I am researching, “How useful are window detectors”. So I am thinking that most homeowners are like me, wanting to keep the costs reasonable when the equipment is adding up fast. So I understand that when away a motion sensor is much more valuable than a window sensor, but when in stay mode motion sensors are disabled. So in the middle of the night scenario I see window sensors as being better but am I needing every window secured. If an intruder has an option, do they ever take a street facing window over a rear facing window? Does the common burglar go for a window that is lit by dusk to dawn lights? And lastly maybe I can give you and idea for another article. What is the top 10 or 15 things I can do to make a burglar pass my home by without a second thought?

  28. Keith says:

    Not sure why you think post is not being watched. Thankfully, I have better things to do than stare at my computer all day waiting for a post to immediately respond to, but here is your reply 15 hours late.
    The main value of window sensors are that if you unintentionally leave a window open, and you are in the habit of always arming your system or at least checking the system status, you will realize that you have done so. As for burglary prevention, even when armed in the STAY mode, I feel that the window sensors are worthless. You can not open a modern window from the outside when they are closed and locked, even with a crow bar as someone earlier suggested. If your windows are left open allowing access, the window sensor would have to be bypassed. If the window is broken, there is an explosion due to the gas that is put in between double pane glass under pressure. The explosion is sure to wake up the homeowner who can press the emergency button to trip the alarm. Hope this info helps you.

    • Hallie says:

      What about burglars who cut or smash a hole into the window just big enough to reach in and unlock the window? Then they would open the window and trigger the sensor.

  29. Conan says:

    Thank you for the response. I had thought it was no longer watched because it seemed like it has been awhile without a response and all of the spam posts in the list. But beyond that now, thank you very much for your response. The information about breaking a modern window causing a loud noise is information I was not aware of and I appreciate it.

  30. dennis says:

    Thanks for the info. I’am updating my older system and plan to add some glass breakage and motion detectors. Can I mount the glass breakage, above the center set of windows on the wall, or does there have to be a direct line of sight from the glass breakage unit to the windows. I have 3 sets of windows on that wall and all within 18 ft of the glass breakage unit, so it would be nice to place that unit in that position.

    • Keith says:

      A glass break detector is a sound activated device. When the unit’s microphone picks up a sound within a decibel and frequency range created when glass is broken, the alarm is tripped. They are typically mounted on the ceiling and have a range of about 25′. I am not a big fan of these units as they are a big source of false alarms, but for some people they are useful.

      Stay safe!!

  31. Steve says:

    If intruders look for unlocked windows, then window sensors are valuable. Can’t tell you how many times wife and kids closed a window but didn’t lock it. Alarm sets just fine but burglar could come right in. Window sensors sound the alarm much earlier than a motion detector would. The wireless alarm industry is trying to justify the costly sensors it would take to properly secure your home. It would put the cost on par with a traditional alarm and you would have a ton of batteries/sensors to replace over time.

    • alarm2000 says:

      I am not sure how an intruder can see that your window is not locked from looking outside, but even if they could, and opened that window to enter a home, the motion detector would deploy the system immediately since an entry door did not open before the motion detector tripping. You are not gaining a lot of time by putting sensors on your windows, but you are making for a more complicated system that is much more expensive. The expense may keep a person from getting a system at all, and a complicated system tends to not get armed because of the difficulties. Either way, we are not making the home as secure as if we left the windows out in the first place! I appreciate, and respect your opinion, but I do not think that you have your facts straight and whole hardheartedly disagree.

  32. berickson64 says:

    All of this discussion assumes a rational person will be setting the alarm when leaving the home. What about when a teenager is the last one leaving. Do you really think she is going to go around the house every day to make sure no windows are open? An alarm without window sensors will allow arming with a window inadvertently open. The problem is, most alarm systems are sold with one motion detector. That one detector can’t cover all the windows unless it is a little cabin in the woods. So the two choices are a bunch of motions or window contacts and glass breaks. Although there are pet immune motion sensors, they are limited by the size of the animal. My dog stands 40″ tall. Do you think it would be a good idea to ignore all motions from objects that large and smaller? I don’t. Motions are not going to pick up someone entering the window in my daughters upstairs bedroom while I am asleep whether that be a home invader or a lothario.

    Motions are great for small areas with no large pets in an away mode. But you have to look at each system separately and the lifestyle of the occupants.

    We had a burglary once where they came in the dang skylight and took all the jewelry out of the master bedroom. The house had window switches, window bugs and motions in the living areas. But there was no motion in the master or bug on the skylight. Each case is unique. There are no shortcuts.

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  34. Sara says:

    Thank you for posting this. I had a a vehicle break in recently and am installing an alarm to feel safer in my home. A good friend and retired Chicago detective gave me nearly the same advice you’ve written. He stated 99.9% of the time, even just having the stickers makes it not worth the risk for the majority of burglars. There are always exceptions, but for most of us, we just aren’t worth the potential jail time if they’re caught. I was debating on window sensors, and I think this has helped me make a more informed decision. Thank you!

  35. Ryan says:

    shock sensors on every window, which covers open/close and vibration on each individual window.. will set alarm even before glass is broken, as well as motion sensors for when im away from home for a cross zone verification is the only way i would ever protect my family.. Yes, it’s a little more expensive , but my family is priceless and will do what i can to make sure they are safe when we go to bed.

  36. Keith says:

    While shock sensors on every window may make sense for you, for most folks this would be a mistake. First of all, our families are priceless to most of us, but we still live with limited budgets, and we have to make many compromises to live within our budget. The window sensors can easily drive the cost of a system out of reach leaving someone with nothing to protect their family.

    Second, the sensors are very subject to FALSE ALARMS! When someone has a system that experiences false alarms, they tend to stop using the system due to annoyance and fines from their local police. So much for protecting the priceless family if you don’t even arm the system.

    Third, when one has sensors on their windows, they can not arm their system with the windows open without bypassing each window. This is an involved process taking the arming procedure from pressing a button on the way out the door to a 2-4 minute ordeal. If it is that involved, most people with just leave without arming. What was the point of putting sensors on all the windows if you don’t arm the system. A simple system that is easy to arm, and therefor is armed is very effective. An elaborate system that is left off is useless.

    Stay safe, Keith

  37. Patrick says:


    Since window sensors rapidly build up system cost, and you said glassbreak sensors tend to give a lot of false alarms, what’s your advice for stay-mode safety? Since the motion sensors are off in stay-mode, how do I design the system to catch someone that has snuck while we’re sleeping?

    Also, I’m currently in a house with drafty single-pane windows from the 70s. The windows slide left-to-right and there’s a squeeze latch that locks/unlocks them. Would they rate entry sensors, or would they still be modern enough that they are almost impossible to force open?



  38. Keith says:


    You will need to test your windows to see if you can open them from the outside when locked. If so, window sensors might make sense for you. Hopefully you do not have many. If you have kids, using motion while sleeping can be close to impossible, but if not, consider having a means to arm and disarm your system from your bedroom. Then you can have motion active when you sleep.

    When you are home, you are part of your home security. If you can not get your windows open, which you probably can’t, the only way in is through a window left open or glass getting broken. If you leave it open, the sensor is useless anyway, and if someone breaks the glass and comes in through the hole they made, that won’t trip the alarm either, but the sound of the glass shattering will alert you, and you can hit the police emergency button on your keypad or panic button on your remote. If you are in San Diego, call me at 858-277-7885, and I would be happy to schedule an appointment for a complimentary evaluation of your security system.

    Best wishes, and stay safe!! Keith

  39. spork says:

    Just discovered this blog. I’m a hobby installer but I do agree with some of this reasoning. This is good advice for saving money on a alarm install. Doors seem to be the most common place to enter and then you can have good pir detection inside. You could even go without pir if you have sensors on interior doors and closed them whenever you left.

    I would like to have a simpler system but we need to be able to move around the house at night without setting off a pir. they work great for covering my unfinished basement with ground level windows. That one is on during stay mode too.

    However even if newer windows are harder to pry open I would think that some burglars move the window after breaking it for easier entry. I don’t like the cost but I think a glass break and contact does add some helpful protection. My honeywell glass breaks don’t false very often on medium setting. I keep them installed inside each window because curtains and such could prevent them from working.

    I am considering to remove the contact on my patio door. We could go in and out and keep the system on. The glass break would stay active which is probably the only way to get through as we keep a board wedged to lock it. I could also just assign the sensor to only work in away mode

  40. Louise says:

    Hello, we are moving to a new home a want a system but I am not sure about what kind of how many sensors we need! We want automated door locks (deadbolts) which have a built in sensor and are compatible with our system we want. So doors covered there. We have 3 pets under 40 pounds but have 1 child, 1 on the way so I am unsure the motion detector is right for us, to use at night I mean. There is a basement with egress windows, do they need to have sensors? It is an unfinished basement right now. I want to ask our system company too and will, but if they want to sell us stuff it seems that may not be the most helpful. Do you happen to have any site links to statistics you particularly use/trust about window sensors being not as useful? My husband almost doesn’t believe me ha! Thanks

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