To achieve a naked eye 3D effect, the technology directs the light emitted by the two stereo images to the user's left and right eye. Microsoft integrated eye-tracking to compensate for head movements and keeps the 3D effect alive even if the user slightly changes her or his location. There were few technical details, but the demo video shows that the display cannot quite achieve complete transparency and it appears that this technology works only with high contrast objects.
Source: Toms Hardware