i kind of remmember that in the old site there was a rusian guy called him self sato, who made something like that, and also i remmember that someone said that he made it using "optic Sensors" in the monitor... (i dont know what is that)
Watch here: http://goo.gl/iX4SW Deriy explains in his video after 4:01 how it works. I have my doubts though that the guys from your video do it the same way