I have a 1999 SL500, central locking system works fine but when the car is locked the alarm goes off randomly even when parked in garage so no movement from passing vehicles or pedestrians . Wondering if any of you have had this problem and have been able to fix it...

 

remove or replace security horn if separate from the car horns. they can go off by themselves when they go bad.

 

Thanks Brookings! Finally got around to removing the inner wheel arch cover and unplugging the siren, I am now able to lock the car without disturbing the neighbors!

 

My issue on my '99 sl500 which was a beeping sound when I went to unlock the car, not full alarm, that I could only turn off by hitting the panic button twice. Turned out to be a micro switch on the dash glovebox.