EN 50131 security grades: what separates 1, 2, 3 and 4

A grade answers a risk question

Product brochures make the grade look like a quality score. It is a risk category. EN 50131-1 sets four security grades, numbered 1 to 4 in rising order, and the designer is expected to start from the premises: what they are, what the contents are worth, how likely an intrusion is and what kind of intruder to expect.

Those design factors are listed in the preamble of Spain’s Orden INT/316/2011, which brought the European standard into national law. We lean on it for a reason. The text of EN 50131-1 is sold, not published, so this article only states what we could read in open sources: the BSI record of the standard, NSI’s guidance, the Spanish order and public documents from the Italian committee CEI.

The current UK edition is BS EN 50131-1:2006+A3:2020. BSI published it on 30 June 2020 and lists it as current and under review. It covers intrusion and hold-up alarm systems installed in buildings, wired or wire-free, and BSI says it is meant to help insurers, alarm companies, customers and the police specify the protection a site needs.

In the UK the police and the insurer set the bar

None of the UK sources we read assigns a grade to a type of premises by law. Two parties shape the decision instead.

The police come first. Forces in England, Wales and Northern Ireland will only register and respond to systems that meet the National Police Chiefs’ Council requirements. NSI spells out the practical conditions for a remotely monitored system:

• installation and routine maintenance by an installer the police recognise;
• for systems newly installed since June 2019, conformity to PD 6662:2017 and BS 8243.

An NSI approved installer also hands over a certificate of compliance for the installation.

Response is not permanent. Immediate response is withdrawn after three false alarm calls in a rolling twelve-month period, and reinstatement can follow once the cause has been identified and remedial action shown. Scotland runs its own policy, with three response levels.

Then there is the insurer, covered in its own section below.

Grade 2 vs Grade 3 in practice

BIBA, the brokers’ association, says Grade 2 and Grade 3 are the grades most often required. The exact test values sit in EN 50131-1 and EN 50131-6, which you have to buy, so the table only carries what open sources state. Where a number is missing, that is because we could not verify it.

	Grade 2	Grade 3
Anti-masking	Not part of the grade. The police Secured by Design standard asks for Grade 2 “with the addition of anti-masking”	Movement detectors must report masking to the user at setting (BIBA)
Signalling (ATS)	Minimum options SP2, DP1 or SP3 in the table reproduced by the Italian CEI draft	Minimum options SP3, DP2 or SP4 in the same table
Power supply and standby	Standby hours set by EN 50131-6, not openly published. Secured by Design asks at least 12 hours, with mains failure signalled to the ARC	Better mains monitoring and battery back-up (Arts Council England guide). Hours not openly published
User codes	NPCC rules do not allow duress codes	Duress codes can be allowed by the police force on application, in high security premises where the risk assessment makes them essential
Tamper	Tamper checked on panel, keypads and detectors (Spanish Orden INT/316/2011, Annex II)	Same checks plus anti-removal on panel and keypads (Annex II). Detectors that spot being re-aimed (Arts Council England)

Anti-masking is the difference you will meet on site. A thief visits during opening hours and covers a PIR with tape or hairspray. BIBA points out the risk is highest where the public can reach detectors unnoticed, so retail and leisure. A Grade 2 detector may never tell you. At Grade 3 the panel reports it when the user tries to set.

Signalling deserves a second look too. NSI notes that a Grade 2 system may still be advised a Grade 3 or 4 alarm transmission system, because higher ATS grades report faults faster. The Arts Council England guide for museums recommends DP3 or DP4, which tell the ARC within four or three minutes that both paths have failed.

Which grade does my insurer need?

No statute answers this in the UK, so the policy wording does. NSI says the insurer may insist on an alarm and may specify the grade. BIBA gives the usual insurer view: Grade 2E for lower risk homes with an unmonitored system, Grade 2 for higher risk homes and lower risk commercial premises, Grade 3 for high risk homes and most commercial premises. Grade 1 is disregarded. Grade 4 is rarely asked for because little equipment meets it.

The grade is only half the condition. BIBA lists what an alarm clause typically adds: an NSI or SSAIB company for installation and maintenance, a live maintenance contract, the system fully set when the premises are empty, and telling the insurer if police response is reduced or withdrawn. Ask for the ATS grade at the same time. Get the answer in writing before you price the job.

PD 6662 and BS 8243 explained

PD 6662:2017 is a BSI scheme, not a product standard. It describes how an intruder and hold-up alarm system should be assembled from the relevant British and European standards, EN 50131 included, and BIBA notes that in effect it requires every system and every component to meet a grade from 1 to 4. BSI states that only systems aligned with PD 6662 and monitored can receive a police unique reference number (URN), and BIBA adds that the system has to be at Grade 2, 3 or 4.

BS 8243:2021 is the code of practice for designing, installing and configuring systems that generate confirmed alarms. BIBA notes that on a system with a URN the police attend only confirmed activations, and this is the document that sets how confirmation works. Since the 2021 edition, published on 30 June 2021, sequential confirmation is no longer mandatory and any confirmation method or mix of methods is allowed. NSI made the new edition compulsory for its NACOSS Gold and Systems Silver companies from 30 June 2022. The NPCC policy lists BS 8243 as applying under PD 6662, which is why the two always travel together.

The lowest component sets the grade

A system can be divided into clearly defined subsystems, each with components of different grades. Article 3.4 of the Spanish order gives the arithmetic in three lines:

1. a subsystem takes the lowest grade among its components;
2. the system takes the lowest grade among its subsystems;
3. components shared between subsystems must have the grade of the highest subsystem.

So a Grade 2 sounder inside a Grade 3 subsystem pulls it down to 2. A control panel serving one Grade 2 area and one Grade 3 area has to be Grade 3.

The draft of Italy’s CEI 79-3 follows the same logic. Equipment in a sub-installation must carry a grade equal to or higher than the level set for it, and so must the control panel and any shared devices.

Spain puts the grades in the law

Spain is the clearest of the three countries. Article 2 of Orden INT/316/2011, in force since 18 August 2011, assigns each grade by type of site and by whether the system connects to an alarm receiving centre.

Grade	Risk	Intended for
1	Low	Systems with an audible warning that are not connected to an alarm receiving centre
2	Low to medium	Homes, small premises, shops and industry in general that connect to a centre
3	Medium/high	Establishments obliged to have security measures, and other sites required to connect
4	High	Critical infrastructure, military sites, explosives stores, cash and valuables depots

Any establishment legally required to install a connected intruder alarm must reach Grade 3. The authorities can change the grade assigned to a single establishment after weighing its circumstances.

The grade keeps mattering after handover. For Grade 3 or 4 systems an alarm counts as confirmed when three or more signals arrive from at least two different detectors, out of a minimum of three installed, within thirty minutes. The annual inspection changes too. Tamper is checked at Grades 2 and 3. At Grade 3 the engineer must also mask the volumetric detectors and confirm that the event reaches the receiving centre. The order keeps this annex in force until an EN or UNE standard on inspections takes effect, and we have not checked whether one has replaced it. It is still the most concrete clue, in a free official text, to what separates Grade 3 from Grade 2.

Italy works with a Performance Level

For Italy we found no legal table of this kind. The technical reference is CEI 79-3, 2024 edition, on intrusion and hold-up alarm installations.

It classifies the installation with a Performance Level from 1 to 4, reached through a criminal risk analysis for which the standard supplies a method. The grade stays on the equipment and must be equal to or higher than that level. In a reply dated 8 October 2025 the committee confirmed that interconnections running to the control panel must match or exceed the panel’s grade.

One caution. These points come from draft C.1343, put out to public enquiry in 2024, which CEI itself marks as not final. We have not read the published standard.

Before you write a grade on a specification

• Start from the risk and the client, then pick products.
• Ask the insurer which grade and which ATS grade it expects.
• On sites open to the public, price Grade 3 anti-masking detectors from the start.
• If police response is wanted, design to PD 6662:2017 and BS 8243 from the outset.
• Check the grade of every component, panel and sounders included.

For confirmation rules and police response in the three countries, see our article on alarm verification.