3 way behind wall smart switch

Hello all,

I’m looking for a recommendation to add a smart switch but I have some specific requirements that might make it a bit of a pain (I’ll give you the long and short version)

TL:DR - I have 3 switches controlling one light, I need to put a smart switch behind one of them without changing the other switches, the location I’m adding the smart switch is the first one, where the power first arrives and has a neutral. I’m looking for ZigBee or zwave, either is fine. I’m in the UK.

Longer version - I’m looking to convert my outdoor lights to have a smart switch, the switch is right next to my front door so I’d ideally like to put an NS panel there so I can also install an alarm system in the future and use this as the control panel.
The issue is that while the switch for outside is just a simple switch, it’s on a 2 gang switch and the other switch controls my hall light. No problem so far… BUT the hall light is on a 3 way circuit with extra switches at the other end of the hall and one upstairs. So the NS panel is no good for it.
My plan! - first tackle the other switch before getting to the outside lights. Convert the upstairs hall switch where the power comes in to a smart switch, not touching hall switch 2 which is the 4 way cross over switch or the hall front door 3 way switch. Then install the NS panel to the front door switch but don’t actually connect the hall lights to it (won’t work as 3 way) just pair it to the upstairs switch in home assistant instead and leave 2 wires permanently connected. Then sort my outside lights with the NS panel wiring as normal.
Now, I can’t convert the upstairs switch to a full smart switch as it’s 3 gang and also has switches for the bathroom light and bathroom extractor on it.

So I just want a ZigBee or zwave behind the wall style switch that I can use to make that one circuit smart without having to do anything at any of the other switches while still having accurate light state reporting.

Can anyone recommend such a switch? Is there anything?

Many thanks for all your help,

I not familiar with UK electricity but this is how multiway smart switching works. This si simple example but this is how it works regardless of number of switches you use for controlling light.

You have two switches. One switch is master switch other is slave switch. Both of them needs neutral wire. Master switch have live, neutral and light wire connected to it and it can control the light. Slave switch has live and neutral connected and it can’t control the light. it needs live and neutral just for power.
You can use automation to turn the light on/off saying if switch 1 is on than turn on switch 2. The same is for off.
Hope this clarify things.

Hi! Thanks for the reply and confirmation!
The issue is I have 3 switches. The upstairs one (which I want to make smart) the front door switch (I’ll make that one the slave later) and the second hall switch.

The second hall switch is the 4 way cross over switch, which unfortunately I can’t make changes to. So I need a smart switch that can cope with that switch not becoming smart and still reporting the correct state.

Any product recommendations for that, where it’s “in wall” and either ZigBee or zwave?

Thanks again for the help!

I have 3 switches on the stairs controlling two lights bulbs. I called electrician and explained to him what to do. He rewired switches in the way i described. First one is master and other two are slaves.
On a stairs I use zigbee switch for a master and tuya wifi for a slave switches. You you can combine that in home assistant.
i found that bseed touch zigbee switches works best for me as they have metal bracket so i can easily mount them, they are very sensitive on touch and ones with neutral wire acts as a router in zigbee network.

How about products that don’t require one of the switches to be replaced with a slave? I can wire it fine but as I can’t do any changes to that hall switch, I guess it would just need to monitor voltage to give accurate state reflection.

Also due to the switch layout I’d need to be using in wall switches rather than changing the switch front plate. Similar sort of thing to the sonoff mini ones.

I’m not sure will this work with smart switches. You must have or smart switch or smart relay behind old switch to make this work. In one electrical circuit where you have two or more switches controlling one or more lights you can only have one master switch. All others switches have to be slave switches.

Is there a wiring diagram for all the switches?

Here’s the wiring diagram.

Have read up more today and tested a lot of voltages I think I’ve got a plan…

The front door switch has the second switch for my outside lights.
So I’m going to get a sonoff zbmini and install it behind the front door switch meaning don’t have to change anything upstairs or on the hall switch. Then I’ll change the wiring so that the front door switch is wired permanently in one way and install the NS panel in front of the zbmini with the panel controlling the mini through home assistant.

I think that should all work fine… But what do people think?

I used this no neutral trick to install the sonoff mini at my light fixture without changing existing 2 way wiring. Should work for your setup

Oh sorry, just realised if missed them on my diagram. I’ve got neutrals at all the switches. I’m just not going to change anything at any such except the front door.