Code Alarm and the MB factory alarm
FWIW, the Code Alarm preserves the working of the factory car alarm. (See my post above for the one exception - I have disbaled the 'lock doors on start' to avoid having the MB alarm go off - otherwise, the MB alarm functions as designed).
The Code Alarm has a lot of programmable options, as well as a panic button mode. It also offers a starter disable option (you need another - heavy duty - relay for this) but that s/b redundant with the MB alarm remaining fully functional.
One final generic thought on remotes - true for my Code Alarm and the wife's factory remote for the 1999 E320 - hold it under your chin pointed upwards when you press the button and the range is vastly increased (at least 2x) - must be something to do with the skull acting as a parabolic reflector. Of course, you also fry your brains in the process....