Factory installed alarm problem

My parents have a 2002 Blazer that was bought with a factory installed alarm system new years ago. The alarm use to automatically lock the car after you walked away and would make the BEEP BEEP noise to tell you it locked. Now it does not automatically lock or make the sound. You can still lock the doors with the remote but no BEEP BEEP noise. Remote operation is working great but like I said the auto mode is out as well as the sound. I found a push button installed under the dash but when pushed it does nothing that I can see or hear. It was added right by the coupling for the computer hookup. There is a red led on the dash panel that flashes and the SECURITY light does light up on the dash too.They have no paperwork on the alarm and are retired and do not have the cash just to take to Chevy dealer to see what is wrong. Anoybody else have the same problem in the past or heard of anybody else woth this problem. Any help would be appreciated.

Gary
ESFD455

Have you checked the battery in the remotes?
Look in the owners manual for reprogram or battery change procedure.
MT

Under dash is usually a Valet switch - get the name off the alarm and get the instructions online.

I have already changed the bateeries in the remotes. No help there. Same problem. Everything works but just the auto lock option and sound option ( BEEP BEEP) does not work. I will look under dash for the name of the unit and try getting help on the internet with that too..........Thanks....

Gary
ESFD455