Only because the original electrician did not connect the ground to the original switch (the ground was in the box, but not connected... why???)
But no. You *must* have the
- common/power lead
- two travelers
- neutral
- ground (ideally)
So if you have five wires, you're good.
Strangely, it all worked fine manually after I had the first switch installed, but when I went through setup, it wanted both switches installed, so I did that because it apparently needs two. It seems like it would work with one smart and one classic, but they say no. It was like $26 for the set, so I decided to be a good boy and play along instead of experimenting.
My friend was over and installed with me and I said "Holy sh##, welcome to the 21st century!" I thought it was close to magic.
He said "Well, I would expect it to respond to voice commands in the 21st century."
I said, "Well, it's Alexa compatible, so, actually, it does respond to voice commands."
At that point he was suitably impressed.