Thatcham devices: what is a Thatcham Category alarm?

Many new cars are fitted with alarms, immobilisers and other clever devices to improve vehicle security. They protect both your possessions and your car itself from being stolen by opportunist thieves.

The number of different car alarms and security features on offer, and the corresponding level of protection they give can be baffling for a new buyer. That’s without even considering the huge number of aftermarket units available.

Thankfully, an institution called Thatcham Research independently rates these different car alarms and immobilisers by category to give consumers a better idea of the role they play. 

But what is Thatcham Research, and what do these assessment categories mean? Read our buying and selling guide here.

What is Thatcham Research?

Officially known as the Motor Insurance Repair Research Centre, Thatcham Research has been at the forefront of vehicle safety, security and repair standards for over 50 years.

Since the 1990s, the Thatcham Categories for Alarm and Immobiliser systems have set an industry benchmark for manufacturers, allowing consumers to compare and contrast the features that each device offers. 

What is a Thatcham device?

Thatcham devices are the alarms, immobilisers and other vehicle security devices that are assessed by Thatcham Research.

They give these devices a Thatcham Security Certification after an assessment of their features and functions. These ratings are called Thatcham Categories and the certified devices are commonly referred to as ‘Thatcham Approved’.

What are the Thatcham Categories?

Following a change in Thatcham Research’s classifications, there are now seven Thatcham device categories:

Thatcham devices

Thatcham Category 1 – combined alarm and immobiliser

Systems that fall into this class are the cleverest and most complex on the market. 

A Thatcham Category 1 alarm will feature perimeter and ignition detection, and incorporate movement, glass break and/or tilt sensors. There’ll also be a siren powered by its own battery supply that will sound if your car gets broken into.

Immobilisers are also a requirement to pass Thatcham Category 1 tests and have to be passively set – that means without any action from the driver – while a minimum of two operating systems or one control unit used for normal operation must be isolated.

Thatcham Category 2 – electronic immobiliser

Thatcham Category 2 is an immobiliser-only category – alarms are not awarded this status.  

Just like Thatcham Category 1 systems, a Thatcham Category 2 device has to isolate at least two circuits or systems, or one vehicle control unit that’s required for the car to run properly. Again, it has to be passively set.

Thatcham Category 2/1 – alarm upgrade

Thatcham Category 2/1 is achieved if a Thatcham Category 2 vehicle is upgraded by retro-fitting an alarm that meets the requirements of Thatcham Category 1. 

This retro-fitting could potentially lower vehicle insurance premiums. 

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Thatcham Category 3 – mechanical immobiliser

Unlike the Categories above, Thatcham Category 3 immobilisation devices are mechanical, not electric. This means they are physical devices that disrupt how a car operates.

They are generally easy to set and unset, and rules state that they have to isolate a minimum of one operating system required for vehicle use. They can be permanently or temporarily installed. Thatcham Category 3 devices include steering wheel and gear lever locks.

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Thatcham Category 4 – wheel locking devices

Most modern cars fitted with alloy wheels benefit from locking wheel nuts. These make it harder for thieves to steal your wheels, as a special key is needed to remove one of the nuts.

Locking wheel nuts actually count as Category 4 Thatcham devices, which have to be reliable and durable, have a secure key replacement procedure, feature a traceable product and provide resistance to attack.

Thatcham Category S5 – post-theft tracking and recovery systems

The new name for the previous Thatcham Category 5, S5 systems can track the whereabouts of a stolen vehicle, but also have the ability to immobilise the car remotely by capping certain engine functions so the car can be shut down. 

Thatcham Category S7 – stolen vehicle location

Thatcham Category S7 is a new category introduced in 2019 to supersede the previous Thatcham Category 6 and Category 7 ratings. S7 is similar to S5, although immobilisation of the stolen car from a different location is not allowed.

Q class systems – non-categorised aftermarket systems

These can include aftermarket alarms and immobilisers, vehicle marking features, data recorders, vehicle ID and signalling systems, and improved door locks that have not been approved by Thatcham.

The higher Thatcham rating the security systems on your vehicle possess, the more your insurance premium may reduce, as your car should prove harder to steal or break into.