that’s true, I just understood from OP he has already old installation with mechanical switches at both ends working properly than he has most probably all this wiring in place.
You are correct, there’s absolutely nothing wrong with the current switches (toggle), I just want to be able to turn the light on / off using one of the modules and Openhab2
Ok but again make the mind switch from electrics to software. With your 2nd switch attached to S2 you can make use of extended functionality such as trigger any OH action on double or triple clicks or click-and-hold (better if you have momentary type of switches but it also works with on/off type).
Thanks Markus, appreciate the advice but I’d be a very happy boy with the on / off functions alone!
Those you get as well of course.
this is tricky and it’s not possible to my knowledge to do it both ways, just one.
There is way how to do it by insterting relays into the circuit, but I personally dont think it’s really good solution.
usual staircase switch does have master and slaves (can be more than one), master is not necessarily the one which physically switches light in question, this is something you need to know or figure out by current wiring.
The switch which is physically connected to the light will be your new main. Rest of them will be dummy, eg. connected ONLY to L(in) and N, eg. your L(out) will be not used on those.
for the wiring. I’m not familiar with Ireland regulations, but in EU since 2005 it is done like this
as you can see, only master is connected to L and carriing switchable L to the slave, which then closing the circuit, the third wire is carriing L back to the master switch when slave is used to switch light on.
in your new setup you will basically just need to use one L to bring L to the slave which will be used as master from now, and in former master just use L and N to power up your new switch.
And then you’ll need to switch slave and master ON by triggering rules, which I mentioned here.
If you are up to reflashing check this out.
I have a couple they work great.
AFAIK, Ireland also is in the EU (since 01.01.1973) 
But they’ve changed the cabling colors in 2005 ?:
| Function | Label | Color old | Color new |
|---|---|---|---|
| EARTH | E | GREEN/YELLOW | GREEN/YELLOW |
| NEUTRAL | N | BLACK | BLUE |
| LIVE | L(1) | RED | BROWN |
And this should be your current wiring diagram? Correct?
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which does not mean much in terms of house regulations 
But if he is living in new-ish building he should have described setup.
And if he does, he need to replace both switches with smart ones which will not be connected to each other as old are.
Practical wiring often looks nothing like schematics.
This may help in case you have loop-in, loop-out, and both switches brought back to ceiling fitting.
https://www.diynot.com/wiki/Electrics:Two-way-lighting
it’s very unlikely that he will have all needed wires at one spot as shown on this diagram.
In theory it might work, but buildins are not really build that way unless they use star wiring schema.
My house was build at 2009 (so regarding latest regulations for hot wires) and shown connection is simply impossible due to lack of wiring at one spot.
It all depends on how the lights and switches are wired.
I’ve got two places at home where replacing a set of three-way switches with wired in Insteon switches was trivial. Just tie all the live to live, neutral to neutral, and earth to earth, then connect the lamp to one of the Insteon switch’s load outputs instead of the live. Live and neutral went everywhere so the switches worked great. The two switches are then linked so they control each other, and the lights work just right from either switch.
And then I have one lousy light where they wired live and neutral in the light fixture, and just ran live to the switches. Saved them a wire. But it also means I don’t have neutral at either switch. There is a solution in Insteon: a mini-switch goes in the light fixture and switches the load. The wires that run to the switches are converted to live and neutral and never switched. Smart switches are connected to them, and work because there’s power. The two smart switches are linked to the switch in the light fixture, and everything works fine. No new wires needed.
Except that stupid light fixture is 20 feet up at the top of a stairwell and difficult to access safely. Grr. Still haven’t got that one wired.
I’m sure the Fibaro switches can do something similar; they look like they’re small and have terminals to wire into.
Until we know how the wiring is actually connected at those switches it’s hard to give a useful set of directions because there’s a bunch of different ways they could be wired.
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You could be right, but as long as we do not know the current wiring it’s just a guess.
It could also be that the L to S1 loop is just a pure control line, with low voltage and amperage.
if the wiring is twin and earth method as many above, the simplest is add a openhab device that can operate a relay double pole crossover ( in the uk called a intermediate switch ) , it switches the strappers, but only inverts the state
Then you have two options
- 1 try to add more wires and use this
Help with a 2-way switch
Which will allow you to leave your current switches in place and add “smart” to the circuit, but I don’t think you’ll be able to have all wires between light and first switch.
or
- 2 you can just replace both of the switches with something like Sonoff Touch or Sonoff T1 and do it as master/dummy solution.
I personally did second option, as I do have L/N in every old switch I have. Some older buildings (pre 2005) were allowed to use only one wire, which obviously is not gonna work.
And I do like to have an option to literally put dummy switch anywhere I want and still be able to control various lights around the house with it (depends on my rules). This is huge advantage of this setup tho.
It has it’s own flaws, but so far I can somehow solve all of those 
I feel I haven’t given enough information to everyone who’s attempted to help here (all of which I’m grateful for, thank you very much indeed).
The downstairs switch which contains “switched live” for the light I would like to control, happens to contain a number of other light switches, which means that there is a “permanent live” available to power the Aerotec/Fibaro module at this switch, if necessary. I feel like an ass for not pointing this out earlier and I apologise. Does this information change anything at all?
there is always permanent L in switch box (otherwise it would not switch light on)
question is still same, if you want to use fibaro you literally need 6 (5 to be precise) wires in that very box which will be used as per diagram