Hawthorne designs, installs and maintains commercial fire alarm systems to BS 5839-1, across the categories L1 to L5 (life safety) and P1 to P2 (property protection). SSAIB accredited, with ongoing maintenance that keeps the system compliant.
Indicative price for a fire alarm system
Use the Hawthorne pricing calculator for a commercial fire alarm range based on building category, size and configuration.
Quick answer
Every UK commercial property needs fire detection appropriate to the building, set by a fire risk assessment under the Regulatory Reform (Fire Safety) Order 2005. The standard most fire risk assessors apply is BS 5839-1, which defines categories L1 to L5 (life safety) and P1 to P2 (property protection). The category drives the design, the install scope, and most of the cost.
For a full breakdown of the categories and what they cover, see our text-primary hover:underlineBS 5839 compliance guide.
What Hawthorne does
Design. A BS 5839-1 design starts from the fire risk assessment and the building's fire strategy. We translate those into a detailed specification covering category, device count, panel type, signalling, and how the system integrates with door release, sprinklers and any other life safety equipment. The design is auditable and is the document that proves the system is appropriate to the building.
Installation. Cabling, containment, mains feeds, panel siting, device placement, and commissioning. The installation is carried out by SSAIB-accredited engineers and is documented for handover. Installation includes the certificate of completion that the building's responsible person needs for compliance.
Commissioning. Each device is tested, the panel is configured for the building's zone layout, the signalling path to the ARC is verified, and the system is handed over with documentation, training for the responsible person, and the schedule for the first six-monthly service.
Maintenance. BS 5839-1 sets a six-monthly service interval by a competent person. Hawthorne maintenance contracts cover the scheduled visits, certificate renewals, response to faults, and the documentation the building's responsible person needs to evidence compliance to inspectors.
Monitoring. Connection to an Alarm Receiving Centre with dual-path signalling and the appropriate response level, where the building's category and use require it.
Categories at a glance
L1. Life safety, automatic detection in all rooms, voids, ceiling cavities and roofspaces (with limited exceptions). Used in care homes, hospitals, hotels and any sleeping risk premises.
L2. Life safety, detection in escape routes, rooms adjoining escape routes, and high-risk rooms. Used in larger HMOs, smaller care premises and certain commercial buildings.
L3. Life safety, detection in escape routes and rooms adjoining escape routes. The most common category in offices and retail.
L4. Life safety, detection in escape routes only. Used in smaller commercial premises with simple layouts.
L5. Life safety, custom design for a specific risk identified by the fire risk assessment.
P1. Property protection, automatic detection throughout the building. Often required by insurers in addition to the life safety category.
P2. Property protection in defined parts of the building (typically high-value or high-risk areas).
For the full breakdown including the rules for each category, see the text-primary hover:underlineBS 5839 compliance guide.
Sectors we work with
Care homes. L1 fire detection with nurse call integration and staff alerting. See the text-primary hover:underlinecare home security guide.
Schools and academies. L2 or L3 across teaching spaces, with L1 in boarding accommodation where present.
Warehouses and industrial. Typically L3 or L4 for life safety, with P1 or P2 added by insurers for property protection. See the text-primary hover:underlinewarehouse security guide.
Offices and multi-tenanted commercial. Usually L3 across escape routes and accommodation rooms, with the building's overall fire strategy setting the specifics.
Retail and hospitality. L3 as a baseline, with higher categories where the building has sleeping risk (hotels, B&Bs) or where the fire risk assessment specifies more.
Cost ranges
L4 or L5 in a small commercial unit: £1,500 to £4,000 installed.
L3 in a typical office or retail building: £4,000 to £12,000 installed.
L1 in a larger or higher-risk building (care home, hospital, multi-storey): £15,000 to £45,000+ installed.
Annual maintenance is normally 10 to 15 percent of the installed value. For a wider breakdown of all commercial security systems, see the text-primary hover:underlinecommercial security cost guide.
Compliance and accreditation
BS 5839-1. The British Standard for fire detection and alarm systems in non-domestic premises. The basis for design, installation, commissioning and maintenance.
SSAIB. Independent inspectorate certification covering fire detection installation. Required by most insurer schedules.
Fire detection to BS 5839. Fire systems are designed, installed, commissioned and maintained to BS 5839, the British Standard your insurer and fire risk assessor work from.
Regulatory Reform (Fire Safety) Order 2005. The legal duty on the building's responsible person to ensure fire detection is appropriate, maintained, and tested. The fire risk assessment is the primary evidence document.
Frequently asked questions
Do I legally need a fire alarm in my commercial premises?
In most cases yes. The legal duty under the Regulatory Reform (Fire Safety) Order 2005 is that fire detection is appropriate to the building and its use. For almost all commercial premises, "appropriate" means a BS 5839-1 system. The category is set by the fire risk assessment.
How often does the fire alarm need to be serviced?
BS 5839-1 sets a six-monthly service interval by a competent person, with a weekly user test on a sample of call points by trained staff in occupied buildings. Skipping maintenance is the most common reason a fire system stops being compliant.
Can you take over an existing fire alarm system?
In most cases yes, subject to a site visit and an audit of the existing system against the current standard. Where a takeover is not practical (system end-of-life, missing documentation, non-compliant install), we say so during the survey and quote a replacement option rather than starting on a system that cannot be brought to standard.
Do I need monitoring for the fire alarm?
Connection to an Alarm Receiving Centre with response is required for some building categories and uses, particularly where the building is unoccupied at certain times or where there are sleeping risk residents. The fire risk assessment sets the requirement.
What is the difference between L category and P category?
L categories (L1 to L5) are designed to protect life by giving occupants time to evacuate. P categories (P1 and P2) are designed to protect property by detecting fire early enough to limit damage. Many commercial buildings end up with both, set by the fire risk assessment and the insurer's schedule respectively.
Designing or upgrading a fire alarm system?
Use the pricing calculator for an indicative range, or contact us for a free site survey and a fully itemised BS 5839 design and quote.
About the author
Dr Andrew Threadgold is Co-Owner of Hawthorne. Hawthorne acquired Security Solutions Yes Limited in December 2024 and rebranded as Hawthorne in January 2026. The technical content of this article was reviewed by Hawthorne's engineering team.
About Hawthorne
Hawthorne is a commercial security and fire systems company working with businesses, care providers, schools and industrial customers across the East of England. Co-Owner Dr Andrew Threadgold leads the commercial side of the business; the engineering team is based in NR6, Norwich.
Last updated: May 2026