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Hi!
This is my first post in this board, but I have read quite a few threads here and learned lots of interesting info.
I was just wondering if anyone had any insight into bypassing magnetic reed switches?
I have been thinking. Since the door can be open a small amount before the alarm sets off, would it be possible to open the door about an inch, then place your own magnet on the part of the switch that is wired in to the system?
Also, can anyone give me any info on where I would be able to obtain a magnetic reed switch to practice different disarmament techniques on it?
In short, learn me about magnetic reed switches.
[last edit 11/29/2008 9:57 AM by Foreveryseason - edited 1 times]
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Okay, I found a couple threads from 2003 on how to defeat them, but I am still interested in any info available and where I could obtain a switch to practice with.
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Posted by Nimabine
Okay, I found a couple threads from 2003 on how to defeat them, but I am still interested in any info available and where I could obtain a switch to practice with.
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There's 2 basic forms used in door alarms. When the magnet (door) is near, the circuit will be either held open or closed (Pulled towards the door). As the door opens, its magnetic field's pull weakens, so the circuit will close or open, respectively, setting off the alarm.
In order to use a magnet to trick a reed switch, you'd have to know which of those two types it is, AND the polarity of their magnet. You'd want to know exactly where along the door frame the switch is. And if it's even behind a thin steel sheet (Door or door frame!) you can forget about using any reasonably-sized magnet to manipulate it. This isn't because steel blocks magnetic fields, but basically redirect them along the plate.
Cheap things that probably contain reed switches to play with: http://shop.ebay.c...ed+alarm&_osacat=0
You could also check Family Dollar for any kind of "home alarm" with a niblet you stick on the edge of a door and a large box for the door frame. Those also contain a simple magnetic reed switch, and it will tell you very insistently if you fail to trick it.
It's pretty much a crapshoot. 50% chance for the polarity and switch mechanism, and a low chance your magnet has a chance to push the reed (Correct location and field penetration). Good luck, and blow a few bucks to see if you can do it despite my pessimism.
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Posted by AnAppleSnail
In order to use a magnet to trick a reed switch, you'd have to know which of those two types it is, AND the polarity of their magnet. You'd want to know exactly where along the door frame the switch is.
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1) You can tell which way the magnetic field is, and possibly find the magnets, with a compass.
2) You don't need to know if it is normally open or normally closed... it is normally influenced by a magnetic field, so that is the state in which it needs to remain. (On most good alarms the switch will be closed when influenced by a magnet, and the device will have a specific resistance.)
I've considered using this trick to get into the library at school after hours. The advantage would be that I'd be able to insert a magnet from the inside before hand, making it quite easy.
"That's just my opinion. I would, however, advocate for explosive breaching, since speed and looking cool are both concerns in my job."-Wilkinshire | |
If you have a dollar store type place near you, you can get a small door alarm unit that runs on batteries and has a magnetic reed switch and a magnet. These usually have two parts, one a bit larger than a 9V battery, the other smaller which contains a magnet. Crack open the case with the battery/sounder inside and look for the little glass vial with two metal bits inside. Play carefully as they are EXTREMELY FRAGILE! Most that are professionally installed are mounted inside a plastic case resembling a fat nail head and potted with epoxy. The entire contact assembly is usually then stuck into a drilled hole in the door/window opening and pushed up tight against the frame.
Problem with magnetic fields is they tend to be somewhat erratic when you get more than one in a location. If you have a magnet holding a contact closed, and pass a suitably strong magnetic field nearby, it is highly possible the resulting field shape between the magnets would allow the contact to open.
Generally, in residential settings, a window in a bedroom may be set up with one contact and two magnets. This allows the window to be parked a few inches open for ventilation but will allow the alarm zone to be armed. Opening the window farther, or closing it, will result in an alarm. There is a small area where the window may be able to move without breaking contact, but the magnets are generally long thin cylinders and face the contact end on. The area of strongest field is pretty small.
If physically you had full access to a contact and it's corresponding magnet, I'd say your chances of actually bypassing it with another magnet are slim to none. The slightest dropout in magnetic field for even a fraction of a second will cause an alarm. And most windows are programmed to a instant alarm zone.
By all means experiment for sake of curiosity. I'd hook up a reed switch in a circuit with a couple AA batteries and an LED in series and poke around with various magnets. In an active site though, even being slightly out of place with a magnetic field will result in an alarm. Not recommended.
Honesty may be the best policy, but it's important to remember that apparently, by elimination, dishonesty is the second-best policy. -George Carlin (1937 - 2008) |
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