Hold the opposite ends of the key (the bit that fastens to your key ring in one hand and the business end of the key in the other) and pull. This will remove the part with the key teeth on it. You are then left with the alarm part. This then splits into two halves - put the unit on a flat surface with the buttons downward, the either prise the two halves apart with your fingernail or a small screwdriver. As you remove the top section, the battery will be exposed. To reassemble, just reverse these instructions. When reassembling the key part will only fit back onto the alarm part one way so don't force it if it doesn't go first time. There is a slot on the alarm section that the key part has a corresponding lug to. Pretty sure you don't need the key resetting. Good luck!
Chris, October 2007
