The experimental Daydream 6DoF controllers and faceplate use photodiodes coupled with artificial intelligence to track the position and orientation of the controllers to support the full six degrees of freedom. (Check out the Degrees of Freedom document for more info.)
Full 6DoF tracking requires that the LEDs on the faceplate are visible to the photodiodes on the controllers. Any obstruction to the line-of-sight between the faceplate and controller causes the controller to suspend position tracking, and will fall back to operating like the 3DoF controller. When the line-of-sight between the LEDs and photodiodes is restored, the system recovers to full 6DoF tracking.
For details on how your users will experience the controllers and faceplate, see Features.