Check out the Xbox One’s Kinect camera. It’s always on, by default. The sensor is perpetually monitoring visual and audio information that it uses to make gesture and voice prompts easier to use. These are features. They can be disabled if the user turns off the sensor or pauses it, but the whole thing is just too darn creepy in theory.
Google Glass is even creepier, because it’s someone else who may be recording you. Forget about the unsavory notion that someone may be watching a funny cat video or furniture porn while having a conversation with you. That person can be recording you at the bus stop from across the street or looking up Foursquare check-ins while scanning the pub.