An apparatus for employing ambient light collected from an external light source to detect a user's fingers that are gripping at least a relatively transparent portion of a case. The ends of a plurality of waveguides are coupled at relatively unequal or equidistant positions to the interior surface of...http://www.google.com/patents/US7551814?utm_source=gb-gplus-sharePatent US7551814 - Optical detection of user interaction based on external light source
