I was riding my bike through Central Park in the New York City Five-Borough Bike Tour last May, where I notice every 50 yards or so a Marshall saying over a bullhorn "Stay to the left please", over and over and over and over again.
How about a bullhorn with a record function, that way you just say "Stay to the left please" just once, then either press a button every time you want to have the bullhorn repeat what you said OR have a setting where the bullhorn constantly repeats what you said, you can adjust the time delay in between repititions via a dial on the side.
Just for fun, add a few switches to tweek the pitch of your voice in case you don't like how you sound when you hear you own voice (Ever hear yourself on a friends answering machine?). Add a Darth Vader voice modulator as well, why not?-- Pac-man, Jan 23 2007 You could have the bullhorn automatically randomize the pitch and speed of the recording slightly on each repetition so that the bullhorn- holder wouldnt get tired of the phrase too quickly.-- Rory O'Kane, Feb 28 2011 Wow, one of those "You mean they don't have this already?" ideas.
How about adding a text input as well so you could have a robot voice saying what you need said? You could pick from various voices too.
Maybe a menu of most often used lines like "Please stay to the left", "Resistance is futile", "Do not attempt to loosen your restraints" etc.
[+]-- doctorremulac3, Feb 28 2011 I thought it involved using an actual parrot... [+] anyways.-- FlyingToaster, Feb 28 2011 random, halfbakery