The Sky does have a general alarm installed already...when we went to pick up our Sky, we wanted to quietly sit in it while waiting for the Sales guy to finish up with a different customer...opened the door and the "beep, beep, beeps" started up. Of course it completely drew everyones attention to the idiots trying to get in the Sky as everyone in the place stood up or looked over to see who was touching the car. The sales guy jumped up and grabbed the keys to stop the alarm. Then my wife says "OK everyone, the alarms work just fine, please go back to your desks now!"
Anyway, I think the addition to the alarm would work fine, but just remember that the Sky is a new car syle and you won't have to worry too much about it being stolen...who could they actually sell it to, everyone would say "isn't that "insert name" Sky? Not enough of them out there to steal and sell, or steal and chop. The motion sensor would most likely go off all the time as people tend to come up to check out the car all the time. I personally think the alarm would become a hassle.