My story Part 2 :

I have since purchased 2 new keys from MB dealer.
They do not have the red dot.

But ....
No matter what I do, the alarm does not go off.

(For example)
I can trunk lock the vehicle using the old red-dot key, and unlock the drivers side with a new key -- no alarm.

Are the new keys just like the old red-dot key?
Is the alarm being set with the new keys?
Do I still need to replace the drivers side sensor chip?

Sorry about the long story MT, but it may be worth something when you get your keys and start tinkering with the alarm.