Sound Tossing is a project that combines shoe-tossing (the act of throwing a pair of shoes onto overhead wires) and DIY audio electronics.
Small sound generators hooked up to loudspeakers are thrown onto overhead electric wires, buildings and trees, from which they emit acoustic signals.
The project's prototype "urban cricket" is a solar powered audio device that releases cricket sounds. Other components that can be used to generate sounds are motion detectors, timers and light-sensetive switches.
Sound Tossing (aka "soundfiti") is created by Reinhard Gupfinger from Austria who ran DIY workshops at this year's Ars Electronica Festival. Instructions on how to build a unit is available online. The website does no provide much info on the environmental consequences, so we'll assume that you are supposed to clean up after yourself.
Related: Led Throwies by Graffiti Research Lab.