Note the on-board LED on the Arduino:

Using an 8 ohm speaker rescued from a defunct iRobot Scooba, some radio wire from an underground dog fence, an Arduino Duemilanove procured from http://adafruit.com/, and a tone demo sketch from http://arduino.cc/en/Tutorial/Tone , the kids and I made a Happy Birthday emitter for mom. Happy Birthday Amy! Here are the happybirthdayemitter.pde sketch and accompanying pitches.h [...]

I got my Arduino + Tilt-ball switch circuit to work.