A friend gave this "Echo Mic" (microphone) to my daughter and she's walking around the hose talking and singing into it with loud reverberations. The device is cheap but it actually works. What's cool about it is that it does not use any batteries or external wires (though there is one in the picture). I'm thinking it must be powered by the sound waves in some way. This should explain everything: http://echomic.notlong.com :)

Peripatetic karaoke!