Spontaneous echo effect?
I was thinking of the old teddy bears which let kids talk to them and a chip recorded the sound and talked back. That made me think how creepy it would be to people walking through a Halloween haunt if they suddenly heard their own words repeated behind them. A quick search led me to this site:
It seems pretty inexpensive, but you need to hold down a button to record and push another to playback.
Any electronic geniuses who could create an ambiance prop that records and plays back ever 10-20 seconds or so? Hopefully one that does not involve elaborate reprogramming.
Maybe there is an off the shelf option I am not aware of. That would be welcome too.