This is one of those projects that didn't really work out right.
The concept was that an IR distance device would detect when someone steps onto our porch. When that happens, a ghost would pop up, lights would flash, a fan would blow the ghost's fabric around. This would continue until the screen door was opened. It would also log information like when it was triggered, when the door was opened and so on. This could then be analyzed to determine how often people came to the door at what times, and what our reaction time is like and so on.
At first, I had to compromise the design because I couldn't get a mechansim working to pop the ghost up. I instead left the ghost upright, and just pulled on it with a servo to make it wiggle. Then, I couldn't get any of the sensors to work correctly. I ended up just making it operate for random amounts of time at somewhat random intervals.
The things that did work were the spotlights, eye lights, and motion. I constructed a light box, which the Arduino can be affixed to. It can turn on and off 4 110v mains current outlets, as well as one extra switch. It operates using solid state relays. (see the gallery link for basic design sketches). The eyes were two ultrabright red LEDs. The body was a simple PVC pipe, the head is two pieces of round foamcore which interlock to form a circle. thin white fabric is draped over it which can then blow when the fan turns on.