When you get a quote for a commercial fire alarm, you'll usually see a category such as L2 or M. The category, set out in BS 5839-1, describes what the system is designed to protect, and therefore how much automatic detection it has. The right category for your building should come from your fire risk assessment.
The three families
| Category | Protects | What it means |
|---|---|---|
| M | Life | Manual only. Break-glass call points and sounders, no automatic detection. Relies on people discovering the fire. |
| L1 | Life | Automatic detection throughout the whole building. The highest level of life protection. |
| L2 | Life | Detection on escape routes and in rooms opening onto them, plus high-risk rooms such as kitchens and plant rooms. |
| L3 | Life | Detection on escape routes and in rooms opening onto them, to warn people before the route becomes impassable. |
| L4 | Life | Detection within the escape routes themselves, such as corridors and stairways. |
| L5 | Life | A bespoke system designed to address a specific risk identified in the fire risk assessment. |
| P1 | Property | Automatic detection throughout the building to protect the building and its contents. |
| P2 | Property | Detection in defined areas of high risk or high value only. |
Which category do I need?
Most offices and shops need at least an M system, often combined with an L category (for example "L3/M"). Buildings where people sleep, such as care homes, hotels and HMOs, usually need higher levels of detection, often L1 or L2. Insurers sometimes ask for a P category to protect stock or equipment.
How we can help
We design, install and maintain all categories of fire alarm. If you're not sure what you need, we can carry out a fire risk assessment and recommend a system that meets the standard without over-specifying it.
Published 24 October 2026 by FITZ FIRE & SECURITY. This guide is general information, not a substitute for a site-specific assessment.