Sorry to hear of yet another case of ODBC port being used to gain access to a Fiesta. I have a 2014 Titanium X which was supplied only with the factory immobilized and alarm. That alarm does not include the ultrasonic and Thatcham 1 rating which is standard on the ST. However, both my car as well as the ST have the same common weak point ie the ODBC port.
I have keyless ignition so using Discloc etc was not a very attractive proposition. After some research I found the Cobra 4615 ADD Can Bus Alarm which includes battery backup siren, immobilized and ultrasonic. The system is a 2-1 Thatcham category alarm. Operation of the alarm is the same as before. I have an extra passive fob which needs to be present when operating the vehicle. I checked that my Ford warranty would not be jeopardized. The Cobra solution is less Labour intensive/intrusive for fitting than the Viper 480xv.
Hope this might help. The Cobra system costs c.£500 professionally fitted.