How to Crack Open your Windows and Still Arm your Window Sensors

A fairly common question posed by security system owners is how they can arm their system while still leaving a window cracked open for air flow. One answer is of course to bypass the zone pertaining to the window you want to leave open, but this is likely undesirable. They may only want to open the window a few inches, or perhaps they want to open multiple windows and do not want all those zones bypassed.

A good solution is to simply add a second magnet to the window. This, however, creates a potential for false alarms if the magnets are randomly applied. The good news is that we can employ some long-lost high school physics knowledge to combat this. We just need to remember the magnets’ polarity and how they affect one another.

Using a 2Gig DW10 Thin Door Window contact and its associated magnets, we have set the magnets a few inches apart as they might be applied to a window frame. In this example the polarity of both magnets is in the same orientation up and down. This creates an attracting force between the two and alters the magnetic field lines.

  The sensor in a closed state.

If mounted within 3-4 inches of one another, this creates an area midway between the two magnets where your sensor will register as closed. It also causes the sensor to remain open when mostly but not fully flush with the magnet.

  The sensor in an open state.

What this generally means is that you will need to make sure your windows stay open at a very precise point in order to arm and not set off an alarm. The magnets will have less room for error and so must be optimally placed.

Instead, when the magnets are applied with their orientation reversed from one another, a repelling force is created and the field lines adjust accordingly. This orientation will tend not to substantially alter the intended gap of the magnets. If you are looking at installing the magnets within about 5 inches or less of one another, this is the recommended orientation.

Should you mount the magnets further apart than that, the orientation will not have the same effect.