Dusted off one of my old imps, connected it to a passive IR sensor to create a battery powered wireless PC/Tablet/Smartphone halloween sound effects system… in one afternoon… thanks to the power of the imp.
You can read about it here: www.instructables.com/id/Wireless-Halloween-Sound-Effects
See, I just use a bluetooth speaker, and iPad, and two excitable children (one to watch for trick-or-treaters, and one to press buttons on the ipad) 
But yeah, I’ve been meaning to put a PIR down the path forever. You could do all sorts of lighting effects to make the house look welcoming right up until they are halfway up the path!