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.