About 6 weeks ago I came to this forum asking some questions about how to do some simple robotics. We finished our Halloween project: a Halloween Robot named "Chancellor Darkskull." The servo control and LEDs run off an Arduino, as described in the video. The tracking technology is able to not only detect visitors, but it also tracks their exact coordinate. Then, the robot points itself toward the visitor coordinate and reacts accordingly.
From the Xandem website: "The robot detects visitors when they enter his graveyard, yells at them when they do, and then follows them around with his piercing red eyes. Since The Chancellor knows the exact location of the visitor, he says funny phrases based on where they go. When no one is present, he puts his head down, turns off his eyes, hides his face, and prepares to startle the next unsuspecting victim."
Check out the video here: http://www.xandem.com/halloween-2010