What's the best way to connect a wired magnetic contact stripe to the door, in order to detect whether or not it's open.

I'm not interested with a wireless one, I'm building all the electricity from scratch, so I want a wired one.

The way I thought to do that is, to use a push button interface (in my case, a KNX PBI), and connect it to the a magnetic contact stripe on the door.

On the door the magnetic contact stripe would close/open the circuit and notice the PBI when the door is closed/opened.

My question is, what's the best location to place the PBI? Should I place a switch near the door, and put the PBI behind it?

Should I pull the cables of the PBI far, to the fuse box?


  • This is low-voltage electrical. It Does Not Mix with mains power. Not in any way, shape or form whatsoever. You must use correct wiring methods, or you will fail inspection and your AHJ will deny you an occupancy permit and make you rip it all out and do it properly. Get a book on properly wiring low-voltage. In fact, a better application of your work would be laying conduit for both mains and low voltage systems, conduit is hard to install, but makes all subsequent electrical work easy. Aug 6, 2017 at 17:46
  • I didn't try to imply it should mix in main power. I had in mind a KNX Push button interface, which mixes in KNX low power network, and signals it when the door is open. Here is an example PBI gira.com/en/gebaeudetechnik/systeme/knx-eib_system/knx-produkte/… Aug 7, 2017 at 4:00
  • "Should I pull the cables ...to the fuse box" was the source of my confusion. Low voltage wires cannot run in the same cable, conduit or raceway. For electronics people, it's all about hooking things to things, and nevermind the multicolor spaghetti in between... and that's fine on a bench. For electrical people, the spaghetti is everything. Wiring methods are 90% of the job. Aug 7, 2017 at 4:50
  • @Harper in KNX (and probably any smart electricity) you have a (maybe different) DIN rack for low voltage connections as well. This is because "actuators" or "on off switches" are connected to low voltage, to get commands from buttons, and to high voltage as well, to switch lights on/off, dim them, etc. It doesn't mean you mix them, high and low voltage cable never run in the same track, but low voltage components exist in fusebox. Aug 7, 2017 at 8:08

1 Answer 1


Security systems normally use a reed switch for this purpose.

It is usually mounted on the strike side at the top of the door to detect even a small opening of the door.

Good luck!

  • Hi, But where is the controller that detects it and sends messages to the bus? Aug 6, 2017 at 14:38
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    I am going to assume you are talking about an Arduino or RaspberryPi. There is no controller in the field. You just take your +5 volts to the switch and back to an input on the board.
    – ArchonOSX
    Aug 6, 2017 at 23:14
  • I understand that, but where, physically on the wall, should your Arduino/PBI/whatever sit? I thought of using gira.com/en/gebaeudetechnik/systeme/knx-eib_system/knx-produkte/… Aug 7, 2017 at 4:00
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    I wouldnt mount it on the wall at all. I would mount it in the basement or some other convenient location, like garage or utility room if your house is on a slab, and then run a single twisted pair wire to each switch. I think you are over complicating this by adding a push button interface. You just take power to the switch and back to an input. Then read the input and if it fails then the alarm sounds.
    – ArchonOSX
    Aug 7, 2017 at 20:22
  • I need something to generate a signal if the door is open. I don't want to connect it directly, to, say, a light switch contactor. I'm not sure what you had in mind. What I thought of, is, when main door is open between 9:00AM-12:00AM – send me an SMS. Aug 7, 2017 at 23:47

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