Grade 1 is for a low risk of theft. It applies to a property which is not likely to attract burglars. In the application guide (DC CLC/TS 50131-7), it assumes that a thief is likely to be opportunistic rather than planning a theft and will simply break open a door.

Grade 2 is for a higher risk of theft. Such a property is likely to have something of interest to an experienced thief who is likely to have some knowledge of how alarm systems work and possibly carry some tools to help him overcome a simple alarm system. The thief is likely to check the building for easy access through doors, windows and other openings.

Grade 3 is for a property which is a reasonably substantial risk, one which, might well contain objects of high value so there is good reason to assume it may be broken into. An intruder is likely to be knowledgeable about intruder alarm systems and have the tools and equipment to overcome the system. The thief is likely to get in by penetrating doors, windows or other openings.

Grade 4 is for highest-risk properties. Such properties are likely to be targeted by a gang of thieves who will probably have planned the burglary in advance. They will know how to tamper with the intruder alarm system to prevent detection and can be expected to gain access by penetration of floors, walls and ceilings.