If your problem is that the alarm keeps going off for no reason it is likely becuase the battery that is located in the alarm siren needs be replaced. This was the case on my 2004 SLK32.
There is a way to replace just the battery but MB only sells the siren (and new battery installed) as the replacement part. Siren is located under the plastic panel at the base of the front windshield.
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I had a new Alarm Siren in it cost $155.00 plus one hour labor $85.00 Silver Star World Wide, Ormond Beach, Florida. Most honest and fair around this area. Lonnie.
How to disconnect the car alarm siren on a 2002 SLK 320 
2001 SLK 230
My four wheeler
Lonnie. 
