Piezo Sirens: Whether you get one from Radio Shack or an online catalog, those things have a sickening high pitched sound. I had this brainfart about putting them "around" the patron and somehow wiring them up spin the patron. Not sure if I can word this right.
One goes off in front, then the next one and the next one until they are all on, surrounding the patron for a brief couple of seconds or as one activates the previous one shuts off.
Talk about distraction. You could do that very cheaply and then BAM, slam them with a pneumatic prop. Or an actor scare.
Klaxtons: In the EMS agency I'm affiliated with, they have these square things that "alert" the providers that there is a call. They WAKE UP the providers when they go off, as most EMT's and PARAMEDICS sleep when they can. They make an obnoxious buzzing sound. I remember them being in schools as fire alarm alerts.
I think you can send someone out of their shoes with those things. Anyone know where to get them?