Sony's attempt to quietly patent new controller technologies did not go unnoticed by members of the online press. The Unwired View found that U.S. Patent application 20060282873 was awarded to Sony on December 14, 2006 for a "Hand-held Controller Having Detectable Elements for Tracking Purposes." The patent was originally filed on May 8, 2006 -- exactly one day before the Wii controller was publically demonstrated at E3.
An array of photonically detectable elements, likely to be LEDs, can be mounted or built into a game controller and be sensed by an image capturing device when the elements are oriented at least partly towards the screen.
The image-capturing device proposed in the patent is a camera, though it is unclear if it is a traditional camera like the EyeToy peripheral for PS2.