Can I turn that off and just press a physical button to start Google Now from any screen? I'd rather not have the watch always listening to me or people I'm around for privacy and battery concerns. If any watch can do this, which is the best value or the favorite?
My only experience is with the Moto 360 and that only listens to you when the watch is on (by deliberately waking it moving it to your face or tapping the screen). The Moto X, however, will listen to you while asleep but AFAIK, it's only listening for your launch phrase to open Google Now and not anything else.
For phones with a physical button like the S6, you can set it so a long press will open Google Now. Similarly, with phone that have on-screen buttons, you can drag the Home button up to open Google Now if it's supported.