It's all buried in the walls, so it's very hard to get at much of it. The live feed comes into one switch (SW1) through a solid wall, and then the common from the other switch (SW2) also goes through the walls to the lights. There's no space behind most of the switches because it's an old house and lots of them are old (or at least old-style) bakelite ones.
The only part it's not horrible to get to is the wires L1,L2 which run between the switches — precisely one of which is live at any given time. I can usually get at those from above (under the upstairs floorboards or in the attic, for the downstairs and upstairs lights respectively).
Now, theoretically it would be possible to have a fully-functional remote light switch which can be retrofitted by cutting that wire and installing something (with its own neutral and ideally also live feed) in the middle. All it needs to do is swap L1/L2 over, to change the state of the light.
And as well as toggle it could even be made to support explicit on and off commands by detecting the current flow. That way it can infer the position of SW2 too. And if the bulb is gone or needs testing, you could also have a mode where it's live on both outputs or neither output, without needing the current detection.
Does such a thing exist? Has anyone looked at making one out of separate relays and current sensors? Are there better options for retrofitting remote controls in this situation? Surely it can't be that uncommon?
If I can get to the common terminal of SW2, that's a little bit simpler — it can then be taken as a 'toggle' input to the relay. But I can't actually see devices which cope with that either; they want their own connections to the switch, and they can't just take 240VAC as the manual switch input. Do those exist?
Any recommendations would be much appreciated; thanks!
