I picked up my 2005 GT this past week and this is straight from the owners manual:
The active anti-theft system is designed to warn you in the event of an unauthorized entry to your vehicle and is also designed to help prevent the unwanted towing of the vehicle.
When the vehicle is locked and armed, the active anti-theft system monitors the following:
* Doors
* Hood
* Trunk
* Movement inside the vehicle
* Change in vehicle inclination
Note: The actice-anti theft system includes a motion detection system which monitors the passenger cabin and a vehicle incline sensor which detects changes in vehicle attitude.