I think that Hallowe'en is probably the most popular holiday among home automation enthusiasts; it's certainly the source of a lot of neat ideas for (temporarily) haunting your house.
One of the best "tricks" is to activate your mechanized ghouls, or start creepy sound effects, when the kids approach your home. It's easily accomplished using a variety of Motion detecting switches.
If you've ever been on the receiving end of Hallowe'en pranks, and this year you want to turn the tide, a good solution is the Scarecrow Animal Repeller from Smarthome. It'll blast water towards anything that moves into the area that you want to keep clear. That'll teach the little hoodlums, right?
And it almost goes without saying that you can otherwise utilize these items for plain ol' home automation throughout the rest of the year.