Sometimes the factory alarm goes off immediately when I lock the door(s) on my '92 300E. It doesn't matter whether I lock the trunk or either front doors. Currently, the problem is intermittent. Any insights?

Not to insult you, but I'll ask the dumb question first. Are you using the valet key when the alarm goes off?

mine does the same and i wasnt sure because my car hadn't come with an owners manual. mine will still go off if i unlock my doors by turning the key to the right, and will occasionally do it even when turning it the right way to unlock it. never really made a big deal out of it but it does have some of my curiousity. i plan on hopefully getting keyless entry and remote start on it fairly soon anyways

No.

I had the same problem and noticed that it occurred when one of my doors or trunk was slightly ajar when I locked the car. But this doesn't explain your problem being intermittent unless the door/trunk you are locking itself is ajar.

For keyless entry, here's a DIY thread from awhile back:

http://www.peachparts.com/shopforum/showthread.php?threadid=11777

Good luck..

~Paul

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'91 300E, 208k miles