I have A Clifford 600-G4 system in my NSX. This one has the 'blackjackx' feature, and let me tell you, it really is a pain in the ass. It's gone off with guestionmarks hovering over my head so many times already, and believe me i do know a lot about electronics, and also on alarmsystems. At the other hand it really gives me a save feeling when i leave the car on the street.
Recently i found out that car-thieves (bad spelling), leave the car with this sort of alarmsystem on its spot, but thats because this system comes with a label witch shows a approved alarm (don't know if you have something like that in the stats, its a label on the window).
If you understand how this system is build up (it's like a ethernet-network), you'll understand that it's pretty hard to harwire it. It also comes with a 'smart' alarm controller, which prevents the system from giving false alarm.
Personaly i am not really afraid the car is getting nicked, coz here there only like 10 or 15 driving in the whole country, which makes it not desireble car to steal.
But at the end, if they really want your car they will have it, whatever you do.
Oh yes, nearly forgot, the system including putting it in the car costed here in Holland nearly Hfl 2000,- which is USD 850.........
Hope this helps,
Dutchy