If you unlock the door and, once you have it open, the alarm still goes off, "unlock" the door one more time with the key. That is what I used to have to do to turn off the alarm on my 88 420SEL. This affliction had started after a deluge of rain as well.
Good luck!

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It is a truism that almost any sect, cult, or religion will legislate its creed into law if it acquires the political power to do so. Robert A. Heinlein


09 Jetta TDI
1985 300D