I am planning to replace two two-way switches that control one light with smart switches [that also have touch switch built in]. I want to keep the existing wiring and switch locations (i.e. hall light with upstairs and downstairs switches).

Would this be better served by a master-slave configuration, a scene configurator or 433Mhz slave?

What would I need? I'm planning to use Amazon Alexa for the control in a European live/neutral/earth environment.

  • anything can trigger anything in IOT, it's all about the rules you use to process inputs into output.
    – dandavis
    Jan 8, 2019 at 22:06

2 Answers 2


I've done this with a Sonoff smart relay from Aliexpress.

Link all terminals of both the smart switch and the normal wall switch. Feed power into the "1" or Normally Open contact, and take the load out of "2" or Normally Closed contact

1 -------------------- 1
2 -------------------- 2

it has one drawback: the smart relay thinks that it is on, when the light is sometimes off. I('m looking for a solution to that issue at the moment.


If I understand the scenario correctly, the SonOff mini can do this (or any other smart switch which can run Tasmota firmware).

The SonOff mini exposes a GPIO pin and a local reference to be used as a 'toggle-on-change' input. This has the advantage of the firmware always knowing the relay state, being possible to define a default power-on state (depending on the firmware), and providing full 3-way switching.

You retain the existing 2-way circuit, but it must be isolated from all other circuits. The SonOff mini requires a live and neutral feed, and generates a switched live for the lamp. The existing 2-way circuit will operate as so either switch toggles the 's' input the SonOff - this is even documented in the installation instructions as an option.

Remember, one 'S' terminal is half-mains voltage, the GPIO input is 3v3 above this - so treat the wiring just as if it was a conventional lighting circuit. You need somewhere close to the fixture to fit the SonOff device.

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