In the most basic sense of a car "alarm", yes, it starts honking at you if you open the door when set. I'm trying to state it in a facetious manner.

When compared to other OEM alarms and after-market alarm systems it, well, doesn't really compare. Don't get me wrong, though... I do like being able to remotely lock and unlock my doors and think that the horn will honk if set off, but I don't have too much faith in the OEM alarm to keep any theives away.