EMG : throw it!


«LED Throwies are an inexpensive way to add color to any ferromagnetic surface in your neighborhood. A Throwie consists of a lithium battery, a 10mm diffused LED and a rare-earth magnet taped together. Throw it up high and in quantity to impress your friends and city officials.»

Check out a video at Graffiti Research Lab » LED Throwies
credit to Spreeblick for that great piece of info of urban media technology.