A note before you read. This is general consumer information for Canadian homeowners and renters, drawn from publicly available Health Canada, CSA Group, and Canadian National Radon Proficiency Program (C-NRPP) sources. It is not medical, legal, or warranty advice. Radon results are reported against the Health Canada guideline of 200 Bq/m³; RadonTest.ca coordinates testing logistics and does not interpret individual results.
See your area's radon level on our map — measured results, searchable by postal code.
Key facts at a glance
- The direct answer: no — a carbon monoxide detector cannot detect radon. The two are different gases with different hazards, and a CO alarm is built to sense only carbon monoxide (Health Canada, Carbon monoxide: Overview, 2024).
- A smoke alarm doesn't detect radon either. Health Canada is explicit that "smoke alarms alert you to fires, not carbon monoxide" — and neither device senses radon (Health Canada, Carbon monoxide: Preventing exposure, 2024).
- Carbon monoxide (CO) is a combustion by-product. It is produced whenever fuel is burned, and a CO alarm warns you of dangerous short-term concentrations to prevent poisoning (Health Canada, 2024). The residential alarm standard, CSA 6.19, exists "to protect against acute effects of exposure to CO" (CSA Group / U.S. DOE Building America Solution Center, 2024).
- Radon is a radioactive gas that seeps in from the ground and builds up over time. It is invisible, odourless, and tasteless, and the only way to know your level is to test (Health Canada, Radon — What you need to know, 2025).
- Radon is the leading cause of lung cancer in Canadians who have never smoked, and second overall after smoking. It is linked to an estimated 16% of lung-cancer deaths — more than 3,000 Canadians a year (Health Canada, 2025).
- What actually measures radon is a long-term test detector analyzed by a C-NRPP-certified laboratory, or a C-NRPP-listed continuous radon monitor. The mail-in kit RadonTest.ca supplies is a radon detector (C-NRPP; Health Canada, 2025).
- You need both. A CO alarm and a radon test address different hazards and are not interchangeable — homes should have each.
The short answer, and why it matters
No. A carbon monoxide detector cannot detect radon, no matter how good the alarm is. The same is true of a smoke alarm. These are excellent, life-saving devices for the hazards they are designed to sense — but radon is not one of them.
It's an easy thing to get wrong, and asking is smart rather than naïve. Both radon and carbon monoxide are invisible, odourless, and tasteless; both can build up indoors; both are dangerous. It is completely reasonable to assume that the small unit already on your wall — the one guarding against "the invisible gas" — might be covering radon too. It isn't. The two gases are different in almost every way that matters, and so are the devices that find them. This article explains, in plain terms, why a CO alarm can't sense radon, what genuinely does, and why the safest home has both a CO alarm and a completed radon test.
Two different gases, two different hazards
The reason one device can't cover both comes down to what the gases are.
Carbon monoxide is a combustion by-product. According to Health Canada's carbon monoxide overview, CO "is produced when you burn any type of fuel" — oil, propane, natural gas, wood, gasoline. In a home that means furnaces, fireplaces, wood and pellet stoves, water heaters, dryers, gas ranges, and attached-garage vehicle exhaust. When one of those appliances malfunctions, is poorly vented, or is run in an enclosed space, CO can climb to dangerous levels quickly. The danger is acute: breathing carbon monoxide reduces your blood's ability to carry oxygen, and can affect you before you notice its presence. That's why Health Canada's advice, if your alarm sounds, is to leave immediately and call 9-1-1 — an emergency measured in minutes.
Radon is a radioactive gas that comes from the ground. As Health Canada's fact sheet Radon — What you need to know explains, radon "is a radioactive gas that comes from uranium in the ground that can get into your home undetected." It seeps in through cracks in the foundation, floor drains, sumps, and gaps around pipes, and in a confined space it can accumulate to high levels. The danger here is the opposite of acute: it is chronic. Radon does not make you feel unwell today; the risk is long-term — the more radon you breathe, and the longer you breathe it, the more your lifetime lung-cancer risk rises. Health Canada identifies radon as the number-one cause of lung cancer in people who have never smoked, and second only to smoking overall, linked to roughly 16% of lung-cancer deaths and more than 3,000 deaths in Canada each year.
So you have one gas that comes from burning fuel and threatens you within minutes, and another that comes from the soil under your house and threatens you over years. Different origin, chemistry, timescale, and health effect — so no surprise that they call for different instruments and different units entirely. Carbon monoxide is measured in parts per million (ppm) of air; radon in becquerels per cubic metre (Bq/m³), a unit of radioactivity averaged over a long period. A device calibrated for one has no way to read the other.
Health Canada's own 2025 fact sheet illustrates the contrast: its comparison of annual deaths in Canada places radon-induced lung cancer at about 3,200 deaths a year — more than car accidents, carbon monoxide (about 300), and house fires combined. Carbon monoxide is a serious hazard worth guarding against. Radon, quietly, is the larger killer — and the one most Canadian homes have never checked for.
How a carbon monoxide alarm actually works
A residential CO alarm is a purpose-built instrument. In Canada these devices are certified to the CSA Group standard CSA 6.19, which — as the U.S. Department of Energy's Building America Solution Center summarizes it — covers carbon monoxide alarming devices "to protect against acute effects of exposure to CO." That phrase is the key: the whole design goal is to catch a fast, dangerous rise in CO and sound a loud alarm in time for you to get out.
Inside a typical CO alarm is an electrochemical sensor tuned to react to carbon monoxide molecules in the air and to trigger at specific ppm thresholds. It is engineered to respond to that gas, at those concentrations, on a short timescale. It has no mechanism to sense a radioactive gas, and no way to measure a long-term average — which is precisely what a radon assessment requires. Asking a CO alarm to detect radon is a bit like asking a smoke alarm to detect a water leak: they are simply built for different jobs.
Health Canada reinforces the boundary from the other direction. On its preventing-exposure page, it states plainly that "smoke alarms alert you to fires, not carbon monoxide" — which is why homes with fuel-burning appliances need a dedicated CO alarm in addition to smoke alarms. The same logic extends one step further: neither a smoke alarm nor a CO alarm senses radon, so a radon test is its own separate step. (The digital-display CO units that show a live ppm number are still CO instruments — that readout is the carbon monoxide concentration at that moment, and says nothing about radon.)
What actually detects radon
If your CO alarm can't do it, what can? There are two Health-Canada-recognized ways to measure radon in a home.
1. A long-term test detector, analyzed by a certified lab. This is the method Health Canada recommends for most homeowners. You place a small detector — an alpha-track or electret device — in the lowest lived-in level of your home for a minimum of three months, ideally through the heating season, during which it passively records your radon exposure. You then send it to a laboratory, which reads it and reports your average concentration in Bq/m³. Health Canada advises testing "for a minimum of three months" this way, and notes you can use a do-it-yourself kit or hire a C-NRPP-certified measurement professional.
This is the important part for anyone comparing devices: a long-term radon test kit is itself a radon detector. It may not blink, beep, or show a screen, but it is doing the one thing a CO alarm cannot — measuring radioactive gas over the long stretch of time that gives a meaningful result. The mail-in RadonTest.ca kit is exactly this: a long-term detector, analyzed by a C-NRPP-certified laboratory, with your result reported against the Health Canada guideline of 200 Bq/m³. For a fuller look at how these kits perform, see are radon test kits accurate in Canada, and for placement, where to place a radon test kit.
2. A C-NRPP-listed continuous radon monitor. These are the electronic devices — sometimes called ERMs — that display radon readings on a screen and update over time. C-NRPP maintains lists of continuous radon monitors that meet its performance requirements. A quality monitor can be genuinely useful, especially for watching trends after mitigation, but two cautions apply. First, not every electronic "radon detector" sold online is C-NRPP-listed, and a handful of consumer models have even been recalled — see recalled radon detectors in Canada. Second, Health Canada's guidance still rests on a long-term measurement for deciding whether to act, so a short spell on a monitor is not a substitute for a proper long-term test. We compare the two in long-term radon test vs digital monitor.
A word on "combo" products. Dual-function smoke-and-CO alarms are common and useful, but they detect smoke and carbon monoxide, not radon. You may also see marketing that lumps radon in with other "invisible gases" — read the label carefully. Unless a device is specifically a radon detector (a long-term test analyzed by a lab, or a listed continuous radon monitor), it does not measure radon. No single wall unit covers fire, carbon monoxide, and radon at once, because the third is a fundamentally different measurement.
Why the confusion is so common — and the takeaway
The mix-up is understandable. Radon and carbon monoxide get grouped together constantly in home-safety talk — both called "the silent killer," both invisible and odourless. If you already own a CO alarm, it feels like the box is ticked, and the shared word "detector" only reinforces the assumption that one gadget has you covered.
But treating a CO alarm as radon protection leaves a real gap — and, given that radon is the larger long-term killer of the two, potentially the more consequential one. The honest, non-alarmist summary is this: two separate hazards, two separate protections.
- For carbon monoxide, install a certified CO alarm (Health Canada recommends at least one with battery backup, placed in hallways outside sleeping areas), maintain your fuel-burning appliances, and act immediately if it sounds.
- For radon, run a long-term test in the lowest lived-in level of your home, and if your result is at or above the Health Canada guideline of 200 Bq/m³, take steps to reduce it.
One protects you from an emergency that unfolds in minutes; the other from a risk that builds over years. Neither replaces the other, and a well-protected home has both. For the broader picture of what radon is and how the risk works, see our overview of Health Canada radon testing guidance and our roundup of the top radon misconceptions in Canada.
We sell both, on purpose. A digital monitor watches your levels year-round; only a lab-analyzed long-term test gives you a number you can act on. If you want the monitor we chose to stock — the C-NRPP-approved Airthings Corentium Home — it's $169.99 with free shipping, or $149.99 with a premium test kit (rides in the kit's box).
Frequently asked questions
Does a carbon monoxide detector detect radon? / Will a CO detector go off for radon? No, on both counts. A carbon monoxide detector senses only carbon monoxide, a combustion gas, and warns you of dangerous short-term levels to prevent poisoning. It will not sound in response to radon at any level, because its sensor doesn't react to radon at all — a silent CO alarm tells you nothing about your radon concentration. To check for radon you need a radon test.
Is there a single detector that detects both radon and carbon monoxide? Not in any meaningful way. CO alarms (including dual smoke-and-CO units) are built around an electrochemical sensor for carbon monoxide and are certified to acute-exposure standards like CSA 6.19. Radon requires an entirely different measurement. If a product claims to do both, check exactly what it is certified to measure before relying on it.
What actually detects radon in a home? Two Health-Canada-recognized options: a long-term test detector (an alpha-track or electret device left in place for at least three months and then analyzed by a C-NRPP-certified laboratory), or a C-NRPP-listed continuous radon monitor. A long-term radon test kit is itself a radon detector, even though it doesn't have a screen or an alarm.
Does a smoke alarm detect radon? No. Health Canada states that "smoke alarms alert you to fires, not carbon monoxide" — and they don't sense radon either. Smoke, carbon monoxide, and radon are three different hazards; radon needs its own dedicated test.
If I have a carbon monoxide alarm, do I still need to test for radon? Yes. A CO alarm and a radon test address completely different hazards on completely different timescales — one an acute emergency, the other a long-term cancer risk. Owning one does nothing to cover the other. A well-protected home has both.
How dangerous is radon compared with carbon monoxide? Both are serious. In its 2025 fact sheet, Health Canada estimates radon-induced lung cancer causes about 3,200 deaths in Canada each year — more than car accidents, carbon monoxide (about 300), and house fires combined. Both deserve protection, but radon is the larger long-term risk and the one most homes have never tested for.
Test for the hazard your alarms can't see
If you have a working carbon monoxide alarm, you've handled the acute side well — keep the batteries fresh and the appliances serviced. The piece that same alarm can't touch is radon, and the only way to know your home's level is to run a long-term test. That's the one gap left to close: a simple, one-time step for a risk that otherwise goes completely unnoticed.
Order your RadonTest.ca kit → — lab analysis by a C-NRPP-certified laboratory (with an all-in-Canada analysis option), tracked shipping both ways, and your result delivered with clear Health Canada context.
Sources
- Health Canada, Carbon monoxide: Overview — CO is odourless/tasteless/colourless, can only be detected with a carbon monoxide alarm, and is produced by burning fuel. Modified 2024-11-12. https://www.canada.ca/en/health-canada/services/air-quality/pollutants/carbon-monoxide.html
- Health Canada, Carbon monoxide: Preventing exposure — "Smoke alarms alert you to fires, not carbon monoxide"; CO alarm placement and CSA-certification guidance. Modified 2024-11-12. https://www.canada.ca/en/health-canada/services/air-quality/pollutants/carbon-monoxide/preventing-exposure.html
- Health Canada, Radon — What you need to know — radon is a radioactive gas from uranium in the ground; #1 cause of lung cancer in non-smokers; ~16% of lung cancers / >3,000 deaths per year; long-term 3-month test via DIY kit or C-NRPP professional; annual-deaths comparison (radon ~3,200 vs carbon monoxide ~300). 2025 (page modified 2025-07-11). https://www.canada.ca/en/health-canada/services/environmental-workplace-health/reports-publications/radon-what-you-need-to-know.html
- Health Canada, Radon guideline — Canadian guideline of 200 Bq/m³; "no level that is considered risk free." Modified 2025-09-24. https://www.canada.ca/en/health-canada/services/health-risks-safety/radiation/radon/government-canada-radon-guideline.html
- CSA Group, CSA 6.19, Residential carbon monoxide alarming devices (as summarized by the U.S. Department of Energy, Building America Solution Center) — standard for residential CO alarming devices "to protect against acute effects of exposure to CO." Publication date January 2024. https://basc.pnnl.gov/library/csa-619-17-r2022-residential-carbon-monoxide-alarming-devices
- Canadian National Radon Proficiency Program (C-NRPP), Listed Professional Device and Consumer-Grade Electronic Radon Monitors — C-NRPP lists continuous radon monitors and certifies laboratories and professionals. Accessed 2026. https://c-nrpp.ca/c-nrpp-listed-professional-device/
Radon facts and the 200 Bq/m³ guideline are drawn from Health Canada. The carbon monoxide facts are drawn from Health Canada's carbon monoxide pages, and the "acute effects" description of the residential CO alarm standard is from CSA 6.19 as summarized by the U.S. Department of Energy's Building America Solution Center — not from Health Canada. This article is general consumer information and does not reproduce any non-public material. It is not medical or legal advice; if you suspect a carbon monoxide emergency, leave the building and call 9-1-1.