The Fiesta can be equipped with two types of alarm, depending on the model. The normal Fiesta (zetec, titanium, trend) is only available with the perimeter alarm. The ST has a Thatcham category 1 alarm. This is with interior sensors and door death locks.The perimeter alarm has a simple horn in the boot, and the thatcham cat. 1 alarm has an siren with backup battery in the engine bay.
Testing the systems is quite simple:
Perimeter: Leave a window open, lock the car, wait for 30 seconds and open the door from the inside. The alarm goes of.
ST Thatcam cat. 1: Leave a window open, lock the car, wait for 30 seconds and just put your hand trough the open window, after a couple of seconds the alarm goes of.
If your Fiesta is equipped with the keyless entry option, leave the key fob out of the signal range. Otherwise the car knows you're there and deactivates the alarm system.