My house has LOTS of double switches, I kind of hate it… I’m looking to upgrade everything to be controllable via Home Assistant, but I’m confused about what to do about these switches.
For example do you install just 1 smart switch and leave the other switch as a standard or do you replace them both as a smart switch?
Thanks for any advice (and I’d love hardware suggestions as well)
Depends on what you buy. If you buy shelly 1 or sonoff mini, you use 1 and attach your existing switches to it. If you buy ‘real’ switches (the ones you put visible in the wall box), you might need to buy 2. Check the documentation if they allow an external (dumb) switch to be attached.
What is a double switch?
serial connection - No. 5?
2v1 Alternately - No. 6+6?
You buy 2. Wire one smart switch to control the light and the other is powered up but does not switch the light. The light control wires are connected together so that there is always power to the light at this point.
Now you have two options.
The advantage of option 1 is that it continues to work if home assistant is offline.
Or you buy one of these, and re-use your existing switches by putting them parallel.
Best would be to use a pulse switch, but that can also be solved by putting a piece of foam inside the switch so it acts like a pulse switch 
That is not how two way toggle DPDT switches work.
That would absolutely be required for your method to work.
All switches remain. Or are you walking through the house with your cell phone in your hand and switching? Add Sonoff mini can fit directly under one of them.
@tom_l
I re-used my SPDT switches and made them pulse 
Figured a piece of foam was cheaper then buying a new switch (which was thrice as expensive as the whole dimmer 
)
What is that an image of?
EDIT: oh I think I get it. Foam to make the switch spring return. No chance of arcing setting them on fire I hope?
@tom_l : Ney, it is on the outside, just under the plastic switch cover 
@francisp : haven’t seen that tasmota before.
I only know the QS-WiFi-D01/2-TRIAC Dimmers, and the 2channel has two switch inputs.
Which one is that???
it wasn’t on the cover and you know it well!
The other option, if there is no neutral at the switch is to put the smart switch near the light fitting. Much easier to get a neutral there. The only issue with this is temperature in the roof space may exceed the devices’ environmental specifications.
A sonoff mini.
Americans call it 3-way switching, the rest of world calls it the correct term: 2-way switching. It’s 2-way because you create 2 possible current paths with the switches, funnily enough using 2 switches… why they call it 3 way is just… American. 
(3 wire connections on a switch does not make it 3-way) Proper 3 way switching uses 3 switches where the one in the ‘middle’ is a special type, a changeover switch.
2-way switching (‘batten holder’ is a light fitting and the ‘L’ terminal on that fitting is just a looping point which doesn’t electrically connect to anything in the light itself. That terminal doesn’t exisint on most light fittings and would otherwise just be a wire connector)
3-way switching
It was there from the beginning. Seriously dude chill out and accept that you overlooked it.
omg
Was there - double switch! I insist!
It might have been. I just realised that title edits do not show a history like posts do.
All switches remain. Or are you walking through the house with your cell phone in your hand and switching? Add Sonoff mini can fit directly under one of them.
