We did something simpler.. We had a covered porch and could get some strobe lights up in there. That was begging for a lightning/thunder simulation, so it was done. I had a computer out of the way with wiring into the neighboring garage. Relays controlled the strobe lights, and I borrowed my honking big game computer's sound system with a serious subwoofer, and hid that behind the plants on the porch. Then added a nice harmless looking doorbell button....
Then we raided the fluroescent paint for danger signs (crossed out and painted over with "WELCOME!!") and glowing arrows pointing to the doorbell button. Add a bunch of other things (tombstones, my wife did a pumpkin with a sword through its "head", etc etc), and use a spare motion sensor to cue some spooky background music sound effects that cut off when the first person steps onto the porch... Add lots of netting that glows purple under UV and it looked really spooky.
Oh boy, it worked very well. We scared the heck out of a few kids, but most thought it was very cool. The funniest reactions were from the 10-12 year olds who realized something was going to happen and were already on edge... They were the ones that yelped or screamed.
Only one set of tears.. and that was a 2-year-old who didn't appreciate the dry ice in the cauldron.
Most of the younger kids got a fright but enjoyed it and wanted to do it again.
I had to quickly add a visual cue when it was rearmed and ready to trigger again. (I used an extra relay output to turn the doorbell light off when the sequence began, and back on again when it was reset and ready again)
I would love to have done a flying ghost though.. Oh well, maybe next year. I'll try a fog chiller instead of dry ice next year too.
And next year, this is being done before the last minute so it can be properly debugged.
Best quotes overheard:
"I'm not pressing it.. YOU press it!"
"DUDE! You're glowing!" (one comment to a friend as they walked up the path)
"That was cool!!"
Various phrases with four letter words not quoted