They make two kinds for the European Models.
One comes standard and has a key fob that arms and disarms it. I think is has some type of chip in it that disables the alarm similar to the GM passkey.
The optional one has a siren mounted in the front clam, and some other switches mounted in the front hood panels, doors and rear engine area and it also has a microwave type motion sensor mounted behind the seats in case you have the roof off.
I think you have to order the optional one when the car is being built, since in order to replace the siren, the front clam has to be removed, and the brains of the unit are mounted inside of the rollbar or targa area before the panels are installed.
Looks like they did this to make it hard for the hoodlums to get to it in order to disable it. It would be nice to get the upgraded one, but we will probably just the standard one.
Just put a pit bull in the passenger seat when the car is left unattended. Nobody will screw with it.