i would like to ask you. I have 3 way switch in on room and i would like to control it via Home Assistant. I have a lot of smart switch with Shelly integrated info HA and everthink is ok, but i dont know how i can connect 3way switch.
Not exactly sure what your picture shows, but if by three way switch you mean two switches in line so you can turn light/etc on/off from two locations then you simply put the shelly at the end point of the circuit. So power enters at first switch, is wired overs to the second switch and then finally hits the end device. Shelly goes in front of the end device.
Yes, it’s doable for your 3 way switch
If you need to avoid adding new cable for the installation, you’ll need to replace your existing switch with momentary type (like those doorbell switch)
The normal way of doing this would be to put the Shelly between switch 2 and the light. So you either put it in the junction box behind switch 2 or in the junction box where the light is connected. For me the placement is driven by what other wires are available at these two locations. You need to have a neutral wire and power available to power the shelly. The load out of switch 2 would go into the S1 port of the shelly.
Three way switches can be tricky. Not all hardware can be used in this situation. Not all three way switches are wired the same either. If you are fortunate to have dead ended three ways it makes it simpler to do but it inevitably comes down to the particular switch you are trying to implement.
I used an Aeotec which has numerous options for three way switches. In my specific case I used the three way switch circuit to operate as strictly dry contact and do the actual load switching with the Aeotec.