actually it may be a tilt type sensor.....
well originally it was the tube from a pen and they put 2 pins in each end so when a ball bearing rolled on to the pins they closed the contacts as a tilt detector......
but there was another way...... I want to use a single pin in each end for detection and by doing this i would set up a oscillator type thing and when the bearing hit the single pin it changes the capacitance and throws off the clock somehow creating a trigger