So you are looking for a fun DIY project to try for Halloween this year? This Animatronic Robotic Skull with motion detection is worth a shot. The robot looks for any motion and animates to scare victims.
You are going to need a MakerClub Hornet Microcontroller, Tower Pro Micro Servos, LEDs, 1 x PIR motion sensor, a 3D printer, and a few other parts to get started. More information is available on Instructables.