CapacitiveSensor lets you create sensors that can detect touch or proximity.
http://www.pjrc.com/teensy/td_libs_CapacitiveSensor.html
http://playground.arduino.cc/Main/CapacitiveSensor
http://www.youtube.com/watch?v=BHQPqQ_5ulc
CapacitiveSensor was originally written by Paul Badger and is now maintained by Paul Stoffregen.
