What if your computer could detect your presence? Developers finally started realizing that there are several ways a person can control a computer besides keyboards, mice and touch screens. These days there are many alternatives, obviously based on hardware sensors, and the main difference is the dependency on software computation. In facts solutions based on computer-vision (like Microsoft Kinect) rely on state of the art software to analyze pictures captured by one or more cameras.
Here are some few ideas
Lean back fullscreen
If the user moves further from the screen while a video is playing on the focused window, the video will go automatically to fullscreen.
If the user is not in front of the screen, the notifications could be shown at fullscreen so the user can still read them from a different location.
This concept is described by Christian Giordano @ Canonical Design blog. Christian also posted a video mockup of this concept, in which he uses “computer-vision”, a face recognition library: