A fire alarm system exists to give people enough warning to get out. Everything else about it follows from that: how much of the building is detected, how the warning is raised, how quickly it reaches everybody, and whether anyone is listening at three in the morning. BS 5839 is the standard the trade designs to, and the fire risk assessment is what decides which part of it your building needs.
The categories, in plain terms
Category M is manual only: call points and sounders, no automatic detection. Category L systems protect life, L5 to L1 in increasing coverage, with L1 detecting throughout. Category P systems protect property, P2 in defined areas and P1 throughout. Most commercial buildings land on L2 or L3. The category is a design decision that comes out of the fire risk assessment, and a quote that does not name one is not a quote for a designed system.
Conventional, addressable and wireless
A conventional panel tells you which zone. An addressable panel tells you which device, which matters when the building is large enough that finding the zone takes minutes you do not have. Wireless systems remove the cabling problem in occupied and historic buildings at the cost of battery management. None of the three is inherently better; the building and the evacuation strategy decide.
Testing and servicing, and who does which
Weekly testing of a different call point each week is a duty holder task and is recorded in the log book. Servicing by a competent engineer is normally at six monthly intervals under BS 5839, covering the panel, the batteries, a proportion of devices, the sounders and the cause and effect. The article 17 duty to maintain is what makes both of those legal obligations rather than good practice.
Monitoring, and what it buys
Monitoring passes an alarm to an alarm receiving centre and then to a keyholder or the fire and rescue service. It matters in unoccupied buildings and in sleeping risks. It is not a substitute for detection coverage, and it introduces its own failure mode: a monitored system whose contract has lapsed looks exactly like one that works.
What moves the cost
Number of devices, which follows from the category. Cabling and whether the building is occupied. Panel type. Whether existing containment can be reused. And for servicing, the number of devices and visits per year. The cheapest install is usually the lowest category, which is a decision about life safety rather than about price.
Questions people ask about fire alarm system
How often should a fire alarm be tested?
A weekly test of one call point, rotated around the building and recorded, plus servicing by a competent engineer at the interval the system's design standard and the fire risk assessment set, commonly six monthly.
What is the difference between L1 and L3?
Coverage. L1 is automatic detection throughout the building. L3 covers escape routes and rooms opening onto them, so that people can leave before the escape route is affected.
Is a wireless fire alarm system acceptable?
Yes, where it is designed and installed to the relevant standard. It is common in occupied, listed and hard to cable buildings, and it needs a battery replacement regime.
Do I need fire alarm monitoring?
The Order does not require it. The fire risk assessment decides, and it usually matters most where the building is unoccupied at night or where people sleep on the premises.