Keyless remote not working. on 2002 Audi A6 Quattro

First my keyless remote stopped working and I figured it was the battery and I wasn't in a hurry to replace it. But just the other night the actual key wouldn't open the door. What can it be?

Asked by for the 2002 Audi A6 Quattro
you key has two components:
(1) remote transmitter that unlocks the doors and trunk.
may use a replaceable battery; some like BMW recharge the
permanent battery
(2) a metal key that fits in the door tumbler and/or the
ignition switch

if the metal key no longer works, it could be the key is
worn out or the tumbler in the door is defective. try your extra key and see if that works. also try both keys on the trunk lock. you may need a whole new key; available only from the dealer.