My car's central locking/alarm remote control (with new batteries) has stopped working. How 2 fix??

This is the spare one that I used after two years and found not working. This is the system that was in vougue in 1990 and around. The one that makes one loud noise when it locks and three loud beeps when unlocks.|||if the system is 17 yrs old, it's probably worn out. depending on how concerned you are about having your car stolen, i'd either remove it or replace it.