Alarm going off for no reason

If I park and lock my 1999 C280, often the alarm will go off for no apparent reason. The alarm will trigger from anytime 15 minutes after locking to about one hour after locking. It only sounds for about 15
seconds and then shuts off. After about 1/2 hour it goes off again. Is there a known cause for this type of behavior?
Thanks, EJ in NJ
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I thought they fixed it... it was a typical problem for the older MB... mainly the W126, but not the 202 that I know of. It is usually the switch on the driver door that does that but that was during the key phase of MB... I am not sure if 99 is remote or not.
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