Land Rover Repair: alarm arming, solenoid, corrosion

Question
When locking my 1998 disco 1 with the keyless remote, the vehice immediately
unlocks after pressing the lock button. I was thinking about replacing the
remote battery, but am unsure of the procedure and if it will require
reprogramming. Any ideas about what else to check would be greatly
appreciated!

Answer
Unlocking right away usually means there is a problem with the driver door latch.  It's binding from rust or corrosion and the lock solenoid can't pull it all the way down, so it pops back up when power is released and that has the same effect as pulling up the door unlock button.

The cure is lubrication (sometimes) or a new latch/lock unit