@B.Will TY, much appreciated.

@RossG Thanks. One more question, If I didn't want to buy the Kit, can I just get one smart switch, model HS200? Or will only the HS210 KIT switches work in a 3-way configuration?

I have a light switch at the top and bottom of the stairs. Can I install just one TP-Link smart switch at either the top or bottom of the stairs or do I have to install them in pairs? I only see the...