A fire alarm system is an integrated network of devices designed to detect fire at an early stage and warn building occupants so they can evacuate safely. The right system for your premises depends on its use, size, occupancy, and the fire risks present.
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What is a fire alarm system?
A fire alarm system comprises several interconnected components that work together to:
- Detect fire automatically (through smoke, heat, or other sensors) or manually (via call points)
- Alert building occupants using audible sounders (bells, sirens) and visual indicators
- Initiate other fire safety actions (such as door releases, lift recalls, or suppression systems)
- Provide information to occupants and emergency responders about the location of the fire
The system must be designed, installed, and maintained to ensure it will work when needed and give people enough warning time to evacuate safely.
A fire alarm system is not just about detecting smoke or heat. It's about providing early warning that gives everyone enough time to escape safely, especially those who may need assistance or are unfamiliar with the building.
Why fire alarm systems matter
The purpose of a fire alarm system is to save lives by:
- Early detection — Identifying fire in its earliest stages, often before it's visible to occupants
- Rapid warning — Alerting everyone simultaneously, regardless of where they are in the building
- Consistent response — Ensuring the alarm activates regardless of time of day or who's present
- Supporting evacuation — Giving people the time they need to get out safely
Most fire deaths occur at night when people are asleep and cannot smell smoke. A working fire alarm system provides critical early warning that can mean the difference between life and death.
Types of fire detection
Fire alarm systems use different detection technologies depending on the fire risks present:
Smoke detectors
Detect visible or invisible smoke particles in the air. There are two main types:
Optical (photoelectric) detectors:
- Detect visible smoke particles using a light beam
- Good for detecting slow-burning, smouldering fires
- Suitable for escape routes, corridors, bedrooms
- Less prone to false alarms from cooking or steam
Ionisation detectors:
- Detect invisible smoke particles using ionised air
- Good for detecting fast-flaming fires
- More sensitive but more prone to false alarms
- Being phased out in many applications
Heat detectors
Respond to temperature rise rather than smoke:
Fixed temperature detectors:
- Activate when temperature reaches a set point (typically 58°C or 78°C)
- Suitable for kitchens, dusty areas, smoking rooms
- Slower to respond than smoke detectors
- Won't detect smouldering fires
Rate-of-rise detectors:
- Activate when temperature rises rapidly (typically >10°C per minute)
- Faster response than fixed temperature
- Suitable for areas with high ambient temperatures
Multi-sensor detectors
Combine smoke and heat detection technologies:
- Use algorithms to analyse signals from both sensors
- Reduce false alarms while maintaining sensitivity
- Better performance in challenging environments
- Increasingly becoming the standard for new installations
Carbon monoxide detectors
Sometimes integrated with fire alarm systems:
- Detect CO gas from incomplete combustion
- Required in sleeping accommodation with fuel-burning appliances
- Not a substitute for smoke/heat detectors
- Additional protection layer
Smoke vs Heat Detectors
Smoke Detectors
- •Faster response to most fires
- •Essential for sleeping areas
- •Required in escape routes
- •Suitable for general areas
- •More prone to false alarms in kitchens
- •Standard for life safety systems
Heat Detectors
- •Slower response time
- •Not suitable for sleeping areas
- •Ideal for kitchens and garages
- •Good for dusty/steamy areas
- •Fewer false alarms
- •Typically for property protection only
Bottom line: Smoke detectors are the primary choice for life safety. Heat detectors are supplementary, used in areas where smoke detectors would cause too many false alarms.
System categories (BS 5839-1)
BS 5839-1 defines fire alarm system categories based on the coverage they provide. The category you need depends on your fire risk assessment.
L-category systems (Life safety)
Designed to protect lives by providing early warning:
L1 — Maximum protection:
- Detectors in ALL rooms and circulation spaces
- Earliest possible warning
- Required for: high-risk sleeping accommodation, evacuation strategies dependent on early warning
- Most comprehensive and expensive option
L2 — Additional protection:
- L3 coverage PLUS detectors in specified high-risk rooms
- Risk rooms might include: plant rooms, storage areas, areas with ignition sources
- Common in: care homes, hotels, larger offices
L3 — Escape routes protection:
- Detectors in all escape routes (corridors, stairways, hallways)
- Provides warning while evacuation routes are still usable
- Common in: offices, shops, small hotels, HMOs
L4 — Escape routes in defined areas:
- Detection only in escape routes within specified parts of the building
- Less common, typically where different risk levels exist
- Must be justified by fire risk assessment
L5 — Tailored system:
- Coverage defined specifically by fire risk assessment or fire engineer
- Custom solution for specific circumstances
- Must be clearly documented and justified
P-category systems (Property protection)
Designed primarily to protect property, not for life safety:
P1 — Full property protection:
- Detectors throughout building to detect fire in earliest stages
- Minimise property damage and business interruption
- Often linked to alarm receiving centre
- Common in: warehouses, industrial premises with valuable stock
P2 — Defined areas property protection:
- Detection only in specified high-value or high-risk areas
- Protects specific assets rather than whole building
- Must be supplemented by L-category system for life safety
M-category systems (Manual systems)
M — Manual call points only:
- No automatic detection
- Break-glass call points at exits and on escape routes
- Occupants must discover fire and raise alarm manually
- Only suitable where premises are continuously occupied during hours of use
- Generally NOT adequate as a sole system
Your fire risk assessment determines what category of system you need. For most premises with sleeping accommodation, public access, or vulnerable occupants, an L-category system is required. P-category systems do not replace the need for life safety systems.
System grades (A-F)
BS 5839-1 also classifies systems by grade, which indicates the power supply and monitoring arrangements:
Grade A:
- Systems monitored by an alarm receiving centre (ARC)
- Continuous remote monitoring
- Faults and alarms reported immediately
- Required by insurers for high-value premises
Grade B:
- Non-monitored systems with central control equipment
- Fault and alarm indicators at control panel
- On-site monitoring only
- Most common for general commercial premises
Grade C:
- Non-monitored systems with power supply from mains and standby battery
- Simpler control equipment
- Suitable for smaller premises
Grade D:
- Mains-powered system with battery backup in each device
- Interconnected detectors (wired or wireless)
- No central control panel
- Common for small premises, residential
Grade E:
- Mains-powered with no battery backup
- Not recommended for new installations
- Does not meet modern standards
Grade F:
- Battery-powered detectors only
- NOT interconnected
- Does not constitute a "system" under BS 5839-1
- Only suitable for domestic properties (not covered by Fire Safety Order)
Most commercial and public premises require at least a Grade B, Category L3 system as a minimum. The exact specification should be determined by your fire risk assessment and may need to be higher depending on risk factors.
Components of a fire alarm system
A typical fire alarm system consists of:
Control panel
The "brain" of the system:
- Receives signals from detectors and call points
- Activates sounders and visual indicators
- Displays alarm and fault locations
- Provides power to system components
- Logs events and maintains records
- Interfaces with other building systems
Detection devices
As described earlier:
- Smoke detectors (optical/ionisation)
- Heat detectors (fixed/rate-of-rise)
- Multi-sensor detectors
- Each assigned a unique address in addressable systems
Manual call points
Break-glass units:
- Positioned at exits and on escape routes
- Within 30m travel distance (typically)
- At each storey exit
- Easily visible and accessible
- Standardised red colour
- Labelled "FIRE ALARM"
Sounders and visual indicators
Warning devices:
Audible sounders:
- Bells, sirens, or electronic sounders
- Must be audible throughout premises
- Typically 65dB(A) minimum (or 5dB above ambient noise)
- Different tones may indicate different zones or alert phases
Visual alarm devices:
- Flashing beacons
- Required in noisy environments
- Essential for hearing-impaired occupants
- Becoming more common in public buildings
Interfaces and auxiliary functions
Additional capabilities:
- Door release mechanisms (magnetic fire doors)
- Lift recall (bringing lifts to ground floor)
- HVAC shutdown (preventing smoke spread)
- Suppression system activation
- Remote signalling to monitoring centre
- Voice evacuation systems (in complex buildings)
BS 5839 standards
The British Standard for fire alarm systems:
BS 5839-1:2017 — Fire detection and alarm systems for buildings. Code of practice for design, installation, commissioning and maintenance of systems in non-domestic premises
This standard provides:
- System categories and grades
- Design requirements and calculations
- Installation standards and cable requirements
- Commissioning procedures
- Maintenance and testing schedules
- Documentation requirements
Other related parts:
- BS 5839-6 — Domestic premises (houses, flats)
- BS 5839-8 — Voice alarm systems
- BS 5839-9 — Emergency voice communication systems
BS 5839-1 is not legally mandatory, but it represents best practice and is widely recognised by fire authorities, insurers, and courts. Following it demonstrates you've taken reasonable steps to meet your fire safety duties.
Testing requirements
Regular testing is essential to ensure your fire alarm system will work when needed.
Fire Alarm System Testing Schedule
Activate a different call point each week. Check all sounders operate. Record test in logbook
Visual inspection of control panel, check for faults, review log of events
Professional inspection and testing by competent person. Test sample of detectors
Comprehensive service and testing. Test ALL detectors. Update service records
Detailed inspection and verification of all components and coverage
Weekly testing
The responsible person (or nominated deputy) should:
- Activate a different manual call point each week (rotating around the building)
- Verify that all sounders activate throughout the building
- Check the control panel correctly identifies the activated call point
- Silence and reset the alarm
- Record the test in the fire alarm logbook, noting:
- Date and time
- Call point tested
- Any faults or issues
- Name of person conducting test
Weekly testing must be recorded. The fire service may ask to see your logbook during inspections. Missing or incomplete records suggest the system isn't being properly maintained.
Periodic and annual servicing
Must be carried out by a competent person (typically a qualified fire alarm engineer):
Six-monthly service includes:
- Visual inspection of all equipment
- Test sample of detectors (rotation basis)
- Check control panel functions
- Verify power supplies and battery backup
- Test sounders and visual indicators
- Review fault log and event history
Annual service includes all the above plus:
- Test ALL detectors (every device in the system)
- Full functional test of control panel
- Check all interfaces and auxiliary functions
- Verify cable connections and terminations
- Test backup battery capacity
- Update system documentation
The engineer should provide a service certificate detailing work carried out, any defects found, and recommendations.
False alarm management
False alarms are a significant issue:
- Cause disruption and loss of productivity
- Lead to "alarm fatigue" where occupants ignore alarms
- Waste fire service resources
- May result in charges from fire brigade
Common causes of false alarms
Environmental factors:
- Cooking fumes
- Steam from bathrooms
- Dust from building work
- Aerosol sprays
- High humidity
- Insects in detectors
System issues:
- Wrong detector type for location
- Poor positioning (too close to kitchens, bathrooms)
- Ageing or contaminated detectors
- Electrical interference
- Loose connections
Human factors:
- Accidental activation of call points
- Malicious false alarms
- Testing without proper notification
- Contractors working without system isolation
Reducing false alarms
Practical steps:
- Right detector for location — Heat detectors in kitchens, optical smoke detectors in circulation areas
- Proper positioning — Away from air vents, steam sources, dusty areas
- Regular maintenance — Clean detectors, replace ageing units
- Staff training — Understand system, know how to respond, report issues
- Consider multi-sensor detectors — Better discrimination between real fires and false alarm triggers
- Investigation — Record and analyse every false alarm to identify patterns
- Delay or two-stage systems — In appropriate circumstances (not sleeping accommodation)
Never disable detectors to prevent false alarms. This removes fire protection and could have fatal consequences. Address the root cause instead.
When is a fire alarm system required?
There's no simple "yes/no" answer. Your fire risk assessment determines what's needed.
Generally required for:
- Sleeping accommodation — Hotels, care homes, student halls, HMOs (houses in multiple occupation)
- Public buildings — Shops, restaurants, entertainment venues, places of assembly
- Large or complex buildings — Multi-storey offices, industrial premises
- High-risk premises — Where significant fire hazards exist or vulnerable people are present
- Buildings with difficult evacuation — Basements, complex layouts, long travel distances
May not be required for:
- Very small, simple premises with straightforward escape
- Low occupancy with very low fire risk
- Where occupants are continuously alert and evacuation is immediate
- Outdoor or open-sided structures
Guest house prosecuted after fatal fire
A small guest house operated without an adequate fire alarm system. A fire broke out at night in a ground floor room.
- ✗Only battery smoke alarms (not interconnected)
- ✗No fire alarm system meeting BS 5839 standards
- ✗Alarms in sleeping rooms only, not in corridors
- ✗Fire risk assessment did not identify inadequate warning system
- ✗Guests in upper floors had no early warning
One guest died from smoke inhalation. The owner was prosecuted for fire safety breaches and received a custodial sentence. Civil claims for damages followed.
Sleeping accommodation requires a properly designed and installed fire alarm system. Battery smoke alarms alone are not adequate for commercial premises or HMOs. An L3 or L2 system would have provided earlier warning to all guests.
Influencing factors:
Your fire risk assessment should consider:
- Use of building — Sleeping accommodation requires higher protection
- Occupancy type — Vulnerable people need earlier warning
- Building complexity — Large or complex layouts need comprehensive coverage
- Fire risk level — Higher risks require better detection
- Evacuation strategy — Simultaneous, phased, stay-put, or progressive horizontal
- Number of occupants — More people need more warning time
- Familiarity — Visitors and public need clearer, earlier warnings
- Time of day — Night-time occupancy increases risk
Maintenance and servicing
Ongoing maintenance is a legal requirement under the Regulatory Reform (Fire Safety) Order 2005.
Responsible person's duties:
- Ensure weekly testing is carried out and recorded
- Arrange periodic and annual servicing by competent person
- Keep maintenance records and service certificates
- Act on any faults or defects identified
- Review system adequacy as part of fire risk assessment
- Ensure staff know how to respond to alarms
What to look for in a service provider:
Competence indicators:
- Third-party certification (e.g., BAFE SP203-1, NSI Gold, FIA approved)
- Qualified engineers (e.g., FIA-registered)
- Insurance and professional indemnity
- References and track record
- Clear service agreements
Service agreement should include:
- Frequency of visits (6-monthly and annual minimum)
- Scope of work at each visit
- Response time for faults
- Call-out arrangements
- Certificate provision
- Clear pricing
Keep all fire alarm documentation together: original design specification, commissioning certificate, service records, user manual, and testing logbook. You'll need these for fire service inspections and insurance purposes.
Typical service costs:
Fire alarm servicing costs vary by system size and complexity:
- Small system (5-10 devices): £150-250 per service
- Medium system (10-30 devices): £250-500 per service
- Large system (30+ devices): £500-1,500+ per service
Annual service agreements often include both 6-monthly and annual visits at a reduced overall cost.
Frequently asked questions
Smoke alarms are standalone battery-powered or mains-powered devices suitable for domestic homes. A fire alarm system is an integrated network of interconnected devices (detectors, call points, sounders, control panel) designed to BS 5839 standards. Fire alarm systems are required for most non-domestic premises and commercial sleeping accommodation.
Installation should be carried out by qualified fire alarm engineers certified to relevant standards (e.g., BAFE SP203-1). Incorrect installation can result in inadequate protection, false alarms, and invalidated insurance. DIY installation is not recommended and may not comply with BS 5839 or satisfy your fire risk assessment.
With proper maintenance, control panels and sounders typically last 10-15 years. Detectors should generally be replaced after 10 years maximum, as they become less reliable with age due to dust accumulation and sensor degradation. Your service engineer will advise on component replacement.
Faults should be repaired immediately. While waiting for repair, you may need to implement compensatory measures such as increased fire patrols, temporary fire wardens, or restricted use of affected areas. Your fire risk assessment should include procedures for system failures.
Usually, yes. Sprinkler systems protect property and control fires, but they're not designed to provide early warning to occupants. Most premises with sprinklers still require a fire alarm system for life safety. The alarm system may be able to be a lower category in some cases.
Most HMOs (houses in multiple occupation) require a minimum Grade D, Category LD2 system under HMO regulations. Larger HMOs may need Grade A or B, Category L2 or L1 systems. Check with your local authority licensing team for specific requirements.
During a planned fire drill, the alarm should sound for sufficient time to ensure everyone has heard it and begun evacuation. It can then be silenced to allow normal communications during the drill. However, the system must be fully reset afterwards, not left in a silenced state.
BS 5839-1 requires sounders to achieve at least 65dB(A) at any point within the building where people may be present, or 75dB(A) at the bedhead in sleeping accommodation. The sound level must also be at least 5dB above ambient noise levels.
Modern wireless systems meeting BS 5839-1 can be just as reliable as wired systems. They use secure radio communication and battery-powered devices. They're often more cost-effective to install, especially in existing buildings. Ensure any wireless system is certificated and properly maintained.
A two-stage alarm provides an initial alert signal (often to staff only) before sounding a full evacuation alarm. This allows investigation of potential false alarms without causing full building evacuation. Only appropriate for premises with trained staff continuously present — never in sleeping accommodation.
Next steps
Your fire risk assessment should identify what fire detection and warning arrangements you need:
What is a fire risk assessment? →
If you're responsible for fire safety, make sure you understand your duties:
Who is the responsible person? →
Not sure what fire alarm system you need or whether your current system is adequate? A qualified fire safety professional can assess your premises and recommend the right solution for your circumstances.
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