"The Ravezooka is a musical weapon that shoots powerful "hardcore" sounds based on your target's distance from the instrument. Squeezing the trigger handle initiates sound and a beam of light. As the user moves the Ravezooka around, the frequency range being played changes based on the distance of the person or object in front of the instrument. The closer the target, the lower the frequency range."
Link to wwmna blog entry.
The Ravezooka was created by Benedetta Piantella Simeonidis and Lesley Flanigan. Here's their project page, and you can hear it in action at New York University's Winter Interactive Telecommunications Program show on December 17 and 18.