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 useĀ  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.

30 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.

  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.

  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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  11. hapzfl says:

    GE or Honeywell or something else?

    We will get a glass fiber based phone in the very near future. Any of the systems can handle such a digital phone line?

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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?

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