Alarm Control Unit
 

Just an FYI - adding to the collective knowledge.

2018 C2S at about 5K miles while driving on the highway car gave me an Airbag Fault. Cruise control no longer operational, auto start/stop deactivated.

Per dealer, car needs a new "Alarm Control Unit". Coming from the motherland. Out of commission for an estimated week or so.

Edit: So the dealer now says it is an Airbag Control Unit which makes a ton more sense. Although still seems unlucky to have that go at 5K miles and 3 months old.