There are many Thatcham category 1 alarms on the market but before making a choice you must find out if your vehicle has a category 2 immobiliser already installed. Newer UK spec cars have them factory fitted as standard for the UK market but if your car has not been important by the manufacturer or is very old then it is unlikely to be fitted with a cat 2. A Thatcham category 1 alarm upgrade is all you need for cars with an existing cat 2 immobiliser otherwise choose a cat 1 alarm and immobiliser.

Thatcham category 2 to 1 alarms differ from soft top cars and hard top cars and you will need to buy an alarm with a microwave interior sensor for an open top car. All other vehicles can be fitted with a Thatcham category 2 to 1 alarm with either an ultrasonic interior sensor or microwave sensor.