My 09 Ultra came from the factory with the alarm. I installed the Radio Shack piezo siren for $5.50.
I agree that a Pro. thief would not be hindered by an alarm. I hope it detours people from messing with it in parking lots.
There was a school of thought in the auto industry : A career thief will pass on an alarmed vehicle, because there is an un-alarmed one down the street.
I spent a large (to me) chunk of change on this machine, the alarm was a small price for some peace of mind.