Based on the demo/promo videos, it looks like the watch accept voice input like Motorola's Touchless Control. Right now, anyone can say OK Google when Google Now is up and running to mess with someone's device. Hopefully they take a page out of Motorola's playbook and make it so it only recognizes your voice.
Re: OK Google
I'm certain it will only recognize your voice. Google Glass already has that feature. And I'd be willing to bet that Android Wear is heavily based on the OS running Google Glass.
Originally Posted by Ry