Intruder alarm · PD 6662
Intruder alarm grades 1 to 4: which one do you need?
What security grades 1 to 4 mean, what PD 6662 is, how police response works and how often an intruder alarm is maintained.
What the grades mean
A security grade says what kind of intruder the system is designed to resist. The higher the grade, the more capable the intruder it expects:
| Grade | Risk | The intruder it is designed to resist |
|---|---|---|
| 1 | Low | Little knowledge and a limited range of easily available tools |
| 2 | Low to medium | Limited knowledge and a general range of tools and portable instruments |
| 3 | Medium to high | A comprehensive range of tools and portable electronic equipment |
| 4 | High | Used when security takes precedence over all other factors |
The grade is set from the risk to the premises. Insurers and inspectorates often name the grade they need, so check what a policy asks for before you design.
What PD 6662 is
PD 6662 is the UK scheme for applying the European standards, BS EN 50131, to intruder and hold-up alarm systems. Insurers and the inspectorates (NSI and SSAIB) work to it. The 2017 edition is the current one. It was updated in June 2019 to use undated references, and the notification options moved into BS EN 50131-1.
Environmental classes
Equipment is also given an environmental class, which says where it can be fitted, by the temperature range it works over:
- Class I: indoors with a well maintained temperature, +5 to +40 °C
- Class II: general indoor areas, −10 to +40 °C
- Class III: outdoors and sheltered, −25 to +50 °C
- Class IV: outdoors and general, −25 to +60 °C
Police response
A system with a police unique reference number (URN) gets police response until there are three false calls in a rolling 12 months. A written warning follows after two. Response is withdrawn no sooner than 14 days after the letter, and the URN is deleted if response stays withdrawn for over 6 months.
Police policy is updated from time to time, so check the current version. A false call is an alarm caused by detector activation with no damage or entry, or by a line fault, unless proved otherwise. The installer, maintainer, customer and receiving centre must all filter false calls, following BS 8473.
How often is it maintained?
Trade guides that cite BS 9263 give: one visit a year for a bells-only system, two a year for a monitored system (or one site visit plus one remote check), and two site visits a year for Grade 4. Check the standard for the exact wording.
Standby battery hours
The battery has to keep the system going through a mains failure. The hours depend on the grade. The figures printed in panel makers' manuals are 12 hours for grades 1 and 2, and for grade 3 under PD 6662, 24 hours (or 12 hours if mains failure is reported to the monitoring centre). Grade 4 figures differ between sources, so use the value in the standard. Our battery calculator puts these into an estimate; it is not a compliance check.
Common questions
What is a Grade 2 intruder alarm?
Grade 2 is low to medium risk. It is designed to resist an intruder with limited knowledge and a general range of tools and portable instruments.
Which intruder alarm grade do insurers want?
It depends on the insurer and the risk. Insurers and the inspectorates (NSI and SSAIB) work to PD 6662, so check what the policy asks for.
What is PD 6662?
The UK scheme for applying the European standards, BS EN 50131, to intruder and hold-up alarm systems. The 2017 edition is the current one.
When do the police stop responding to an intruder alarm?
A system with a police URN gets response until three false calls in a rolling 12 months. A written warning follows after two, and response is withdrawn no sooner than 14 days after the letter.
This guide is general information for UK fire & security companies, not legal or engineering advice. Always work to the current edition of the relevant standard and your own competent-person judgement.
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