There are two main types of category 2 Thatcham immobilisers, touchkey and transponder. A touchkey Thatcham immobiliser works by inserting an electronically coded key into a receptacle on the dash board and turning the ignition key within a set time limit. Transponder Thatcham immobilisers are easier to use because the electronically coded keyfob sends a wireless signal to the engine to let you start it normally by turning the ignition key.

A Thatcham immobiliser must isolate at least 2 circuits on the engine to prevent it from starting without a coded touchkey or transponder, the starter motor is the most important to isolate to avoid it turning over and save power. Some Thatcham immobilisers have 3 circuit immobilisation which could include: starter motor, ignition and fuel pump isolation.