Here is a quick project for an electronic Halloween pumpkin that will scare your guests as they approach. A sensor embedded in the nose detects when people get close and can do anything you tell the sensor to do. The project site I found has the pumpkin playing scary sounds and lighting up LEDs on the face.
The sounds are stored on an SD card (like the one you use in your digital camera) so its easy to change and customize what the pumpkin says. The project site says the code is very easy to modify if you want to change what happens.
The project instructions seem well written and comes with lots of pictures to help you along the way. Looks like an easy project for first time sensor hackers/programmers.