How to program the 2000 Nissan Altima remote keyless entry:
Sit in the driver’s seat. Close all of the doors. Push the “Lock” button twice on the driver’s side door panel. Insert the key straight into the ignition, and then remove it six times within 10 seconds. Do not turn it each time.
Insert the key again. Turn it to “Acc.” Push the “lock” and “unlock” buttons at the same time on the remote. Remove the key. Push the “Unlock” button on the door. The remote is programmed.