I got one of these "Mega Sound Blasters" <http://www.amazon.com/Sounds-X-treme-Mega-Sound-Blaster/dp/B000FAKFFK> from American Science & Surplus- currently out of stock, but they seem to get them in every so often. It's a small plastic horn (about 3 inches long) that makes a deep sound above the threshold of pain when you blow into it! Claim is it can be heard a half mile away or more. I don't know how sturdy it is, because I've only tried it once - that was enough!