I was reading Veen's post on having to repair a security alarm in his old KH and made me start thinking about my favorite prank!
I recommend everyone buy an "annoy-a-tron" and place it in their local KH. Simply put, it is a small electronic device that once activated will randomly emit an electronic noise every 2 to 8 minutes. It is incredibly annoying and a fun as all get out! Because the noises are so random and short it is very difficult to locate. It has a built in magnet so it is easy to just find some random place to plant it!
I buy mine from Think Geek: http://www.thinkgeek.com/gadgets/electronic/8c52/
Guaranteed fun!
~IMM