Amazon Fire Phone comes with a 3D head tracking technology which the company is calling Dynamic Perspective. It uses four front-facing infrared cameras to track your head at all time. It also works in the dark. The information captured by the cameras is updated 60 times a second to always display content based on what angle your head is to the display and also enable various tilt gestures in browser, lockscreen and other apps. Suppose you are looking at a picture, the display will change its perspective as you tilt it. In a game that was demoed you could tilt the display to see the entire scene, than what's just in front of you.
Amazon has developed special cameras for the Fire Phone which have a wider 120 degree field of view as opposed to the narrow viewing angles of regular front-facing cameras (about 72 degrees). To capture depth information you need two cameras, so why four ? Because people may block the cameras due to their positioning, so the Fire Phone always uses the two best cameras available to capture "Z-depth" information, i.e. the distance between the phone and your head.
Dynamic Perspective SDK is also available for developers who want to sink their teeth into Amazon's head-tracking tech for innovative uses.
