Alarm Detection Techniques II - The Magnetic Switch

[Psychlonic]

A magnetic switch is a circuit component which relies on a magnet to hold the circuit either open or closed. Usually they hold the circuit closed. The idea works by employing a box with a magnetic lever inside and wire(s) running to and from said box. This lever, when in proper position, connects the wires going to and from the box as to complete the circuit. This box is placed at an opening where a hinged door or window swings away from it. On the door or window is located a strong magnet. When the door is closed, this magnet will be aligned just below the box with the switch inside, as to attract or repel the level into it's proper closed circuit position.

http://www.thetwistergroup.com/store/im ... 3E8600.JPG
http://img.diytrade.com/cdimg/784578/67 ... switch.jpg
http://www.harriscomm.com/catalog/image ... SIT_MS.jpg
http://www.electrical-res.com/EX/10-18- ... ircuit.gif
http://www.asihome.com/images/GRI200-36.jpg


An elaborate variation of this set-up is that the box with the lever is inset into the frame of the window or doorway, and the magnet is set into the door or window itself. This makes the magnetic switch almost impossible to see without opening the door first. This can be taken advantage of if you can conduct recon beforehand while the alarm is deactivated, but often this is a luxury you as an operative won't have.
Similarly, conventional external magnetic switches are dead obvious to detect from one side or another. Again though, the magnetic switch is generally located on the side of the door that you're not supposed to get to, so unless you can conduct prior recon you might not realize it's there.

http://www.asihome.com/images/GRI2020-12WG-W.jpg
http://www.blunet.net.cn/uploads/Sensor ... ntacts.jpg

There are other tricks to detect the magnetic switch, however. Eyesight is the most natural. It may be possible to see the other side of the door using windows and/or mirrors. If there are windows, you should be searching for PIR sensors anyhow, so while you do so, peek over to the door if possible and see if there's an obvious switch. Also be on the lookout for magnetic switches while you are inside of the building and going through doors. The point of using your eyesight is to simply confirm a switch is present faster. If you fail to see a switch with your eyes, this means nothing.
This is where a simple compass comes into play. On any operation where you may need to go through a door, always bring a compass with you. The compass itself must be decent quality and sensitive. Don't bring some cheap Coleman piece of crap you bought at the dollar store along, because it's not going to give you accurate readings here. You're looking for one which focuses on magnets quickly and accurately, and the farther away it can do so, the better. See the equipment section for more on selecting the right compass.
As you can guess, the purpose of the compass is to point directly at the magnetic switch when one is close. If you have a good compass, this is exactly what will happen. Depending on how the magnet is polarized, either the north or south needle will point directly at it. If you move the compass around, the needle follows. This is how you'll know you've found a magnetic switch.
To scan for a magnetic switch on a door, start at the top of the doorway on the opposite side of the hinges. This location is the most frequently used spot to place the switch, as this side of the door moves farther ahead than the other. If it was on the other end, people could crack the door open without sounding an alarm. Nonetheless, scan the entire top end of the door.
This presents a problem. Often, you won't be able to hold the compass level and see where it's pointing. To make matters worse, most compasses work miserably upside down. If you can buy one that works great, do so. Otherwise, you'll need a way to get your eyes to about the same height at the top of the door or window, even if your eyes happen to be looking through a carefully placed mirror above you.
If no switches are found, check the side of the door as well. This is a quick process, so while chances of a side installation are slim, there's not much to lose by scanning anyways. You can also check the bottom and the opposite side if you have reason to suspect an unconventional installation location was used.

If you locate a magnetic switch, whether it be by eyesight or a compass, you may opt to locate a different entryway, or execute the sensor blinding techniques. Be advised that foiling magnetic switches is simultaneously the easiest and the most difficult of tasks. It is near impossible to do so silently from outside, and trivial to do while inside.