Sorry to bring up an old discussion, but I just thought of two phrases: Yep and Nope
It also occurred to me…to differentiate between your WC piston asking a question and Alexa asking a question, you might want to preface any WC questions with question, choice, or decision.
"Decision. Would you like to turn off the TV?"…“Yep”
"Question. Did you take your medication yet?"…“Nope”
[EDIT] Oops…I see Khaled had the same idea for responses. Darn it! 
Interesting… I have never heard Alexa spout off anything without a verbal prompt first. Does your Alexa intrude like that?!?
You are correct that this has happened after I’ve asked her something (like turn off a device). She will occasionally say something like “Would you like me to…blah blah blah.” I never really get to hear it because I’m not ready for it, and don’t know how to get her to repeat it. Even when I do, “yes” and “no” never seem to work, anyways. (I have a piston that will make her repeat something another piston has made her say.) It happens rarely and randomly, but I just had that in mind when I was thinking about your piston. Plus, it would make the piston easier for family members to understand what’s going on.