Circuit bending

Circuit bending is the creative, short-circuiting of electronic devices such as low voltage, battery-powered guitar effects, children's toys and small digital synthesizers to create new musical or visual instruments and sound generators. Emphasizing spontaneity and randomness, the techniques of circuit bending have been commonly associated with noise music, though many more conventional contemporary musicians and musical groups have been know to experiment with "bent" instruments. Circuit bending usually involves dismantling the machine and adding components such as switches and potentiometers that alter the circuit.
- taken from Wikipedia

Here are some useful links about circuit bending.
http://www.getlofi.com
http://www.hollis.co.uk/john/bent/index.html
http://www.anti-theory.com/soundart/circuitbend/
http://www.circuitbenders.co.uk/

Please google for more info.