There is no sensitivity adjustment on a factory system. Maybe someone added a system to it? The alarm will go off if a microswitch in one of the doors, the trunk, or the hood activates it. On some Euro models they also had interior motion sensors and glass breakage sensors, I don't believe this was ever offered on a US vehicle like this one, nor should it cause the alarm to activate inappropriately as this coworker is experiencing.
I would say either a faulty switch or control module, or an aftermarket system is to blame.
The good news is that the anti-theft system stores codes and can give a description of why the alarm is activating (assuming the factory system is to blame), so have him get it to a Mercedes repair shop and get it checked out.