As an exercise to get acquainted with the Arduino micro-controller, I created an apparatus that lets a person use their fingers to send digital signals to the Arduino by tapping on a metal plate. Metal contacts attached to the fingers (index, middle, ring) when touched with a metal plate will light the corresponding LED. When all 3 fingers close the switch, the larger LED turns on. This concept can be extended further by using the finger switches to open a combination lock. The correct finger combination must be pressed down in the correct sequence in order to open the lock. One of 3 small LEDs will light when a finger combination is correct. The larger LED will light once all 3 combinations are entered in the proper sequence.