Is it possible to upgrade the factory alarm on a 2001 E430 (e.g. adding airhorns, sensors...) while retaining the factory remote. Anyone know what company or brand is compatible.

Honestly, you don't need to.
This thing is the hardest car made to steal. With the electronic keys, the only way to take it is to have a key. I couldn't steal one if I wanted.

Upgrade 2001 E430 factory Alarm
 

Thanks for reply, I was also inform by my dealer that the SOS(teleaid) could be utilized as a vehicle locator system, but must be activated. I did recently install a multimedia audio system and would like to be able to protect it with shock or glass mic sensors. I know of somebody who has a E320,left it overnight @ airport parking and someone JACKED UP his audio system at the same time they destroyed his dashboard...seeing it got me itching for an UPGRADE.