I have a staircase lighting system where 2 x 3-way (SPDT) wall switches can operate the lights, and I'd like to automate the lights, to turn them off if accidentally left on, etc etc.   I searched in the forums and found the diagram below. The problem I have is the load wire (the red wire going from L on the right hand side switch to S1, plus the grey wire) is not available in the box where I would need to install the Switch, and running that cable would be a major hassle in my house.