change the battery inside the key fob.
the next bit i had off the net for my daughters key fob
Open the fob casing with a small screw driver or knife
pries the 2 halves apart
take out the Old battery insert the new one + side up
close the fob back together .go to the car hold the fob as close as poss to the aerial
rapidly press both buttons on the key fob 20 to 30 times or until the alarm light flashes RAPIDLY
the fob should now be synchronized and should work as expected
wirecutterman, November 2009
