Do Carbon Monoxide Detectors Detect Gas

No — carbon monoxide detectors do not detect gas leaks. They are designed to alert you to the presence of carbon monoxide (CO), a colourless, odourless, and deadly gas produced when fuels like gas, wood, coal, or oil don’t burn completely. While both natural gas and carbon monoxide can be dangerous, they are very different substances and require different types of detectors for proper monitoring.

If you want to protect your home from both carbon monoxide and gas leaks, you will need separate alarms for each hazard.

The Difference Between Gas and Carbon Monoxide

Natural gas — which powers your boiler, cooker, or fire — is primarily made up of methane, a highly flammable but non-toxic gas. It has no smell in its natural state, so suppliers add a strong sulphur-like scent (often compared to rotten eggs) to help you detect leaks quickly. Carbon monoxide, on the other hand, is a by-product of combustion, meaning it’s created when appliances that burn fuel do not operate properly.

You might smell a gas leak, but carbon monoxide gives no warning signs unless you have a working detector. That’s why these two risks are treated separately, even though they both originate from fuel-burning appliances.

Why Carbon Monoxide Detectors Don’t Pick Up Gas Leaks

Carbon monoxide detectors use sensors designed to detect only CO molecules. They will not react to methane, propane, butane, or other gases used in domestic heating and cooking. If there’s a gas leak in your home — for example, from a broken pipe or an unlit burner — your carbon monoxide alarm will remain silent because it is not calibrated to recognise those gases.

This is a critical distinction. Relying on a CO alarm alone may give a false sense of security if you believe it will warn you of any gas-related issue. It’s important to understand what each device is designed to detect and ensure you have the right alarms installed.

How to Detect a Gas Leak

To detect a gas leak, you need a gas leak detector, which senses the presence of combustible gases like methane and propane. These detectors can be installed in kitchens or near boilers and will trigger an alarm if gas is detected at dangerous levels. Some smart home safety systems combine both gas and CO detection in a single unit, but most homes require at least one of each type of alarm in key areas.

In the absence of a detector, your sense of smell is often the first line of defence against gas leaks. If you ever notice a strong rotten egg smell or hear a hissing sound near gas appliances, turn off the gas at the mains if it’s safe to do so, open windows, and call the National Gas Emergency Service on 0800 111 999 from outside the property.

When You Need Both Detectors

You should install carbon monoxide detectors near any gas appliances, open-flued fires, boilers, or fuel-burning stoves. These devices alert you to incomplete combustion, which can release dangerous levels of carbon monoxide. You should also consider a dedicated gas leak detector, especially in kitchens or near older appliances, to monitor for unburnt gas in the event of a fault or leak.

Neither alarm replaces the other, and both serve an important purpose in home safety. Together, they provide a complete safety net against two very different — but equally serious — risks.

Misunderstandings Around Carbon Monoxide Alarms

Many homeowners mistakenly believe that a carbon monoxide alarm will alert them to any kind of gas danger, including leaks from natural gas appliances. This misconception is understandable, as both natural gas and carbon monoxide are invisible and associated with gas appliances. However, assuming that one device can detect both is a common and potentially dangerous misunderstanding.

A carbon monoxide alarm is not a general gas detector. It has a very specific function — to detect elevated levels of carbon monoxide. It cannot recognise methane or propane, so it won’t activate during a gas leak unless carbon monoxide is also present as a by-product of combustion. That’s why it's important to know exactly what your alarm is designed for and to ensure you have suitable coverage for different types of gas-related risks.

Why Gas Leaks Pose a Different Type of Danger

A natural gas leak is dangerous primarily because it’s highly flammable. If it builds up in an enclosed space, even a small spark from a light switch or appliance can cause an explosion. However, natural gas is not poisonous in the same way carbon monoxide is. Exposure to low levels of natural gas may cause headaches or dizziness, but its primary risk lies in combustion — not toxicity.

Carbon monoxide, by contrast, is dangerous because it binds with haemoglobin in the blood, preventing oxygen from circulating. It’s produced when fuel doesn’t burn completely, often due to a faulty boiler, blocked flue, or poorly ventilated gas appliance. Carbon monoxide is lethal in very small amounts and builds up silently — which is why a dedicated alarm is essential.

The Role of Dual Gas and CO Alarms

Although most standard carbon monoxide detectors do not detect gas, dual-function detectors are now available on the market. These devices are specifically designed to detect both combustible gases like methane or propane and carbon monoxide at the same time. They’re useful in kitchens, boiler rooms, or anywhere gas is used in enclosed spaces.

If you’re installing detectors in a home that relies heavily on gas appliances, a combination unit may offer a convenient and cost-effective solution — but only if it’s clearly marked as such. Always check that the device has been certified to detect both substances and that it meets the required British Standards for gas and CO detection.

Importance of Regular Testing and Maintenance

Just like smoke alarms, gas and carbon monoxide detectors need to be tested regularly. A silent detector isn’t necessarily working — and batteries can degrade without warning. Most modern detectors come with a test button that should be pressed once a month to check for functionality. Replace units as recommended by the manufacturer, usually every five to seven years.

It’s also essential to avoid obstructing the devices. Do not paint over them or place them in cupboards or behind furniture. Detectors should be placed where air can circulate freely, close to the source of potential risk, and installed according to the manufacturer’s instructions or a qualified engineer’s advice.

Final Word

Carbon monoxide detectors do not detect gas leaks. They are designed to alert you to the presence of carbon monoxide only, which is a separate and serious hazard. To fully protect your home, you need both a carbon monoxide alarm and a gas leak detector — each installed in the appropriate location. Understanding the difference could help prevent accidents, health issues, or worse. When it comes to home safety, it’s better to be covered from every angle.