Category 1: Combined alarm and immobiliser
Category 2: Electronic immobiliser
Category 2/1: Alarm upgrade (that is, adding an alarm to a Category 2 system)
Category 3: Mechanical immobilisation (steering wheel, pedal and gear lever devices)
Category 4: Wheel locking devices
Category S5: Trackers and recovery systems
Category S7: Stolen vehicle location
Q Class systems: Non-categorised systems, including aftermarket alarms, immobilisers and data signalling systems not meeting Thatcham approval