Smoke Alarms & CO Detectors in HMOs: What the Law Requires

If your HMO was inspected tomorrow and the officer found non-compliant smoke alarms, you could face a civil penalty of up to £5,000 — and that's before any impact on your licence. The rules for HMOs go significantly further than a standard rented property, and the most common mistake is assuming a few battery-powered alarms from a hardware shop will do the job. They won't.

This guide sets out exactly what the law requires for smoke alarms and carbon monoxide detectors in HMOs in England — broken down by building type so you know precisely where you stand.

Which law applies to your HMO?

There are two routes to the same legal destination, depending on whether your HMO is licensed.

If your HMO is unlicensed, the Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022 apply directly. These came into force on 1 October 2022 and set out minimum alarm standards for all rented residential premises in England, including unlicensed HMOs.

If your HMO is licensed (mandatory or additional licensing), those regulations technically exempt you from Parts 1 to 5 — but only because equivalent requirements are built into your HMO licence conditions under the Housing Act 2004. The practical outcome is the same. Either way, the alarm standards are non-negotiable, and the enforcing body is your local housing authority.

This matters because landlords sometimes read guidance that says licensed HMOs are "exempt" from the 2022 Regs and wrongly conclude they have fewer obligations. You don't — you just have them through a different legal instrument. For a full breakdown of what your HMO licence requires on fire safety, see our guide to HMO licence fire risk assessment requirements by council.

Smoke alarm requirements: what your HMO actually needs

The baseline rule is one smoke alarm on every storey used as living accommodation. But for HMOs, the requirements go further — specifically around the type of alarm and whether they must be interconnected.

1 to 2 storey HMOs

Your HMO needs a mains-powered, interconnected smoke alarm system — classified as Grade D1 under BS 5839 Part 6. This means:

• Each alarm is powered from the mains electricity supply
• Alarms have a tamper-proof 10-year lithium battery backup
• All alarms are interlinked — if one triggers, every alarm in the property sounds

Grade D2 alarms — the kind with a replaceable 9V battery — are largely non-compliant for HMOs. If you're still using those, replace them.

Alarms must be fixed to the ceiling in circulation spaces: hallways, landings, and corridors. Not inside bedrooms or living rooms — in the routes tenants will use to escape.

3 or more storey HMOs

A Grade D1 system is not sufficient for taller HMOs. Three or more storeys requires a Grade A system: a full automatic fire detection and alarm installation with a central control panel, manual call points, and sounders. This is the same category of system used in commercial buildings.

If you own a three-storey HMO and you're running interlinked mains alarms without a control panel, you are not compliant. This is the single most common gap we see in HMO fire risk assessments — and it's one that the complete HMO fire risk assessment will flag immediately.

The kitchen rule: heat alarm, not smoke alarm

Every HMO kitchen needs an alarm — but it must be a heat alarm, not a smoke detector. Smoke alarms in kitchens trigger constantly from cooking fumes, which leads tenants to disable them. A heat alarm responds to a rise in temperature rather than airborne particles, so it only activates in a genuine fire.

The heat alarm must be interlinked with the rest of the system. A standalone battery heat alarm in the kitchen does not meet the standard.

Carbon monoxide detector requirements

Since October 2022, a CO alarm is legally required in every room used as living accommodation that contains a fixed combustion appliance — this includes gas boilers, gas fires, and solid fuel burners. Gas cookers are the only explicit exemption.

In most HMOs, this means a CO alarm in any room where the boiler is located or where there is a gas fire. If your boiler is in a cupboard off the hallway, that cupboard counts. If you have individual gas fires in bedsit rooms, each room needs its own CO alarm.

On placement: position the alarm at head height or above, ideally on the ceiling or at 1.6 metres on the wall, and within 1 to 3 metres of the appliance. In rooms with sloped ceilings, mount it at the highest point.

CO alarms must be in working order at the start of every new tenancy — not just checked annually. This is a legal requirement, not best practice.

Seven mistakes that will cost you

These are the most common compliance failures found in HMO inspections:

1. Battery-only smoke alarms. Non-compliant for HMOs. Must be mains-powered.
2. Non-interconnected alarms. If a fire starts in the ground floor kitchen, tenants on the top floor need to hear it immediately. Standalone alarms do not achieve this.
3. No Grade A system in a 3+ storey property. Interlinked mains alarms are not enough — you need a central panel.
4. Smoke alarm in the kitchen. Replace it with a heat alarm.
5. Missing CO alarms. If there's a gas boiler or gas fire, a CO alarm is required — not optional.
6. Not testing at tenancy start. You must check all alarms are working on the first day of each new tenancy and keep a record.
7. Assuming "licensed HMO = fewer rules." The legal route is different; the standard is not.

Smoke and CO alarms are assessed as part of any fire risk assessment. If your alarms don't meet the grade, your FRA will note it as a significant finding. For a broader look at what inspectors check, see our guide to Fire Safety (England) Regulations 2022 for HMO landlords.

What about Scotland, Wales, and Northern Ireland?

The rules above apply in England only. The other nations have their own legislation:

• Scotland — The Fire (Scotland) Act 2005 and associated regulations apply. Scotland introduced stricter interlinked alarm requirements for all homes (including rented properties) from February 2022, ahead of England.
• Wales — The Renting Homes (Wales) Act 2016 governs smoke and CO alarm requirements for occupied dwellings, with separate HMO licensing conditions under Welsh regulation.
• Northern Ireland — Landlord obligations are set out under separate Northern Irish legislation. Check with the Northern Ireland Housing Executive for current requirements.

If your properties span multiple nations, treat each jurisdiction separately — the England rules do not transfer.

Fire doors and alarms work together

Alarms alert tenants to a fire; fire doors give them time to escape. The two systems are designed to work in tandem — an alarm wakes people up, a correctly rated fire door holds back smoke and flames long enough for them to reach an exit. If you're reviewing your alarm compliance, it's worth checking your HMO fire door requirements at the same time.

Next steps

The alarm requirements for HMOs are specific, graded by building size, and enforced with real penalties. If you're not certain your system meets Grade D1 or Grade A standard, or if you haven't confirmed your CO alarm coverage since October 2022, now is the time to check.

FRASafe guides you through a BS 9792:2025-aligned assessment — free to complete, £45 for the council-ready PDF. It covers alarm type, placement, testing records, and CO detector coverage as part of a full fire risk assessment for your HMO.

Start your HMO fire risk assessment on FRASafe.