kinect sdk > how to check if user is in front

Hi, I'm working with a friend on a school project where we want to display a character and capture the player movement with the kinect. I'm helping him with the art and with unity because none of us are experienced unity programmers(I do AS3).

We are using this wrapper for the kinectSDK (beta 2), everything's running fine and the quality is far superior than what we achieved with OpenNi specifically with filtering and wrists/head movement.

THE QUESTION: How can I check if no one is in front of the kinect?

I'd like to play an animation in that case. This I can do it but can't find how to ckeck that. It doesn't have to be very elegant, we just need it to work to show the concept.

Actually, If I can do this i'll be more than happy: 2 characters on scene (kinect and standard skinned mesh) If kinect is receiving the std character hides, if kinect is not receiving, kinect char hides and std char shows up and plays the animation.

Thanks in advance