I don't want to give up the classical switches, which operates on 220V.
In this way the each light will be almost independent on UniPi, which could be installed in house later.
(Only each relay of UniPi will be replaced by hard-connected cables to simulate 3-way switch)

Why do you thing my design is not possible?

Hello,
would it be possible to use realy in UniPi to replace first switch (3 way, switch #6) , in traveler system of multiway switching?
https://en.wikipedia.org/wiki/Multiway_switching#Traveler_system_2

I would like to control 1 light from multiple places (3 and more switches) and I am thinking about to add additional "pseudo" 3-way switch at beginning of chain which will be replaced by UniPi relay. Switches in the middle will be 4-way (switch #7).

I am aware, that I wound be able to monitor, whether the light is really on or off. Or is there any way?

Thank you for any advice.