i have installed 1/2 of a 3 way kit into a 4-way light.  the switch does work correctly via the paddles or the app.  however, the app doesn't know if the light is on or off.  the app always inidcates the light is off.  the switch is connected to the load end of the circuit.  maybe the switches talk to each other via wi-fi and w/o any communication the default is off?  if it was load or voltage sensing this it should know.

update.  i replaced both of the 3-way switches with TP smart switches and left the 4-way "dumb" switch in the circuit.  This set up is working perfectly for me.

Board4mic, 

Can you clarify the setup you used, are all three switches in the 4-way circuit the TP-Link smart 3-way switches? Or just two of them with a standard switch at one of the locations?

when wiring a 4 way light, you have to use two 3-way switches (HS-210 kit) and one 4-way switch.  the 4-way switch solely has 2 traveler wires coming into it and 2 travelers going out of it.  i replaced the two 3-way switches with the TP link HS-210 switches.  i left the center 4-way switch as it was.  i've included a diagram to help clarify.  so in the picture i replaced the two outside switches.

Thank you, that is very helpful! 

@board4mic  What happened when you installed the 2nd 3-way switch? My guess would be the app recognized the light being on or off.

@Mike1960   that's correct!

@board4mic So at the risk of sounding obtuse, the 1 regular 4-way and 2 Kasa 3-way swicthes works exactly as one would hope:

The app knows if the light is on/off 

The app correctly turns on or off as per request/

Any switch can change the state at any time

Correct?

And thus, in the case you wanted to have 4 or more stations, all the addditional switches would be 4-way?

CONFIRMED WORKING FOR BOTH 4 AND 5 WAY INSTALLATIONS IN MY HOUSE.

I can confirm that a single HS210 kit (with 2 switches in it) worked for both my 4 and 5 way switch configurations.  They should be installed in the "3-way" switch boxes present in each configuration.  I'm not positive which boxes those are or exactly the layout of the wiring as my electrician installed them for me, but an electrican can tell you.  Basically the 2 boxes with the least wires in each case.  For the other switch locations you use normal dumb switches (the Kasa switches will know the on/off state from the presence of power at one of the switches).

A KEY POINT: In order for this to work correctly, you have to set the switches as a pair in the software.  This means you only add ONE SWITCH initally, and then you must choose the "installing 2 switches" option during the set up of that first switch.  It will then have you go to the second switch and hold the button down till the red light flashes.  Once this is done, the two switches show up as a single switch in the software.  They are then able to communicate back and forth if they see power and thus mark the switch as on or off.    If you fail to do this, you will have a number of issues related to turning the lights on and off programatically.  If you do this wrong and you see two switches listed in the software, you must go back and delete both switches and start over.

Great job TP-Link for such a flexible product.