The majority of North American Boxsters are spec'd with alarms that have IR motion sensors that detect movement inside the cabin area. In other words if something moves inside the car, not if the car moves. This should detect someone reaching into the car to grab something, but I don't think it detects the car being towed.
As others have said an alarm doesn't deter the criminal who is equipped with tow equipment, but I guess it will let you know if someone is messing with your car.
Here in Toronto the M.O. of the professional car thief is to break into your home while you sleeping, steal your keys and then simply drive your car away to a waiting container destine for overseas. I don't think the Boxster is one of the sought after models.
And congratulations on your new car.
