Silent Home Hazards
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Do Carbon Monoxide Detectors Detect Natural Gas?

If you can smell gas now, leave first. Get everyone out, touch no switches and light nothing, and call your gas company's emergency line or 911 from outside. A detector is for the leak nobody has noticed yet.

No. A carbon monoxide alarm is built and tested to sense carbon monoxide, and natural gas is a different gas. Under UL's standards they are two different devices: carbon monoxide alarms are covered by UL 2034, and alarms meant to detect flammable gases such as natural gas and propane are covered by UL 1484. Some products put both sensors in one case, and only those products cover both.

Standards and agency pages on this page were read on 20 October 2026.

Two hazards that are easy to mix up

Natural gas is a fire and explosion hazard. It is mostly methane, and on its own it has no color, smell or taste, according to the US Energy Information Administration. Gas companies add an odorant, mercaptan, so a leak smells of rotten eggs. Federal pipeline rules require gas in distribution lines to be odorized so that a person with a normal sense of smell notices it at one-fifth of the concentration at which it can ignite (49 CFR 192.625).

Carbon monoxide is a poisoning hazard. It comes from fuel that burns, and the EPA describes it as odorless, colorless and toxic: there is nothing to smell at all, so only an alarm will catch it.

The two meet at gas appliances. A furnace, water heater or range that burns gas badly can produce carbon monoxide, and a CO alarm will sound for that. It sounds for the carbon monoxide, not for the gas. A gas line leaking unburned gas into the room gives a CO alarm nothing to react to.

How to tell what your alarm covers

Look at the label on the back of the alarm, the box or the manual:

A smoke alarm is a third device again. Some smoke alarms include a carbon monoxide sensor, which the label will say; a smoke alarm does not detect natural gas.

Combination alarms

If your home has gas appliances, a combination alarm covers both hazards from one outlet. We have reviewed two:

Both are compared, with a handheld leak finder for tracing a leak to a fitting, in our gas leak detector collection.

Where each one goes

This is where a combination alarm needs a decision. Natural gas is lighter than air and collects high, so the gas sensor wants a high position: both First Alert's and Kidde's instructions place it near the ceiling for natural gas. Propane is heavier than air and pools low, which flips the advice; see propane leak detectors. Carbon monoxide mixes with room air, and a standalone CO alarm goes where its manual and our CO alarm placement guide say.

Follow the manual for your model. It gives the heights and distances the alarm was tested at.

Questions people ask

Will a carbon monoxide detector go off for a gas leak?

Not for the leak itself. It can go off when a gas appliance burns badly and makes carbon monoxide, which is a different problem with a different fix: leave, call from outside, and have the appliance checked by a qualified technician.

Do I need a gas detector if natural gas already smells?

The odorant works when someone is awake and nearby to smell it. A gas alarm covers the times nobody is: overnight, when a leak is slow, or in a room you rarely use.

Does a carbon monoxide detector detect propane?

No. Propane is also a flammable gas, so it needs a gas alarm too, mounted low.

Does a smoke detector detect carbon monoxide?

Only if it has a CO sensor built in, and the label will say so. Plain smoke alarms don't, and neither kind detects natural gas.

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