I would like to install a Android tablet on a wall. So I would wake it up by looking in to the camera(distance ~0.5 - 2 meters), by clapping my hands or something similar. Now I'm searching for an app or a service who can handle this. Something like ISeeYou, but working... I will only awake my device, not unlock it.
Voice control apps are plentiful, and a few will work with screen off. Keeping the camera on all the time would chew up resources too fast so I doubt you'll find a solution there.
This kid has an app that will let Google Now listen with the screen off and then another app that will let you add additional commands. http://rsenapps.com/