Radon Detector vs Carbon Monoxide Detector:
Which Do You Need First?
One of these silent killers is likely in your home right now. The wrong choice — or worse, no choice at all — could cost far more than the price of a detector. Here is how to decide, based on EPA and CDC data.
By the HomeAirHazards Research Team · Reviewed against EPA and CDC publications · Updated May 2026
The Wrong Choice Costs More Than Money
Radon causes ~21,000 lung cancer deaths per year. CO sends ~50,000 Americans to the ER annually.
The EPA estimates 1 in 15 US homes has radon above the action level. The CDC reports CO poisoning deaths every year from furnaces, generators, and gas stoves. Both are invisible. Both are odorless. Both are preventable with the right detector.
1/15
homes has unsafe radon
50K
CO ER visits per year
Head-to-Head Comparison
| Feature | Radon Detector | CO Detector |
|---|---|---|
| What It Detects | Radon gas (Rn-222) | Carbon monoxide (CO) |
| Hazard Type | Long-term cancer risk | Immediate poisoning risk |
| Source | Uranium decay in soil under home | Incomplete combustion (gas, wood, oil) |
| Detection Method | Alpha-particle ionization or charcoal | Electrochemical sensor |
| Placement | Lowest lived-in level, 20" off floor | Each floor, near bedrooms, near appliances |
| Response Time | Hours to days (continuous monitoring) | Seconds to minutes |
| Short-Term Test Kit Cost | ~$15–$30 | N/A (always continuous) |
| Continuous Monitor Cost | ~$150–$250 | ~$20–$50 |
| Alarm Type | Visual / app notification | Loud audible alarm (85 dB) |
| EPA/CDC Recommendation | Every home should test | Every home must have one |
| Who Is Most at Risk | Basement / ground-floor dwellers, smokers | Homes with gas heat, stoves, fireplaces, attached garages |
Rn Radon — The Slow, Silent Killer
Radon is a naturally occurring radioactive gas that seeps into homes through foundation cracks, sump pits, and crawl spaces. You cannot smell it, see it, or taste it. The EPA classifies radon as the second leading cause of lung cancer after smoking — responsible for roughly 21,000 deaths per year in the United States.
The danger with radon is cumulative: the longer you breathe elevated levels, the higher your risk. There is no "safe" level, but the EPA action level is 4.0 pCi/L. Testing is the only way to know. Most real estate transactions now require radon testing because of how common elevated levels are.
Short-term charcoal test kits give you a snapshot in 2–7 days. Continuous electronic monitors like the Airthings Corentium give you real-time readings and track trends over months. Both approaches are valid — short-term kits for a quick check, continuous monitors for ongoing peace of mind.
If your home tests above 4.0 pCi/L, the EPA recommends installing a radon mitigation system. A properly installed system typically reduces radon levels by 99%. The cost of not testing — and not knowing — is measured in years of life.
CO Carbon Monoxide — The Fast, Silent Killer
Carbon monoxide is produced whenever fuel is burned incompletely. Gas furnaces, water heaters, stoves, fireplaces, generators, and even cars running in an attached garage can produce dangerous CO levels. Like radon, CO is invisible and odorless — which is exactly why the CDC calls it the "silent killer."
Unlike radon, CO kills quickly. At high concentrations, CO poisoning can cause loss of consciousness within minutes and death shortly after. Even at lower levels, chronic exposure causes headaches, dizziness, nausea, and confusion — symptoms easily mistaken for the flu. The CDC reports approximately 50,000 emergency department visits and over 400 deaths per year from accidental CO poisoning in the US.
CO detectors are inexpensive and work similarly to smoke alarms — they sound a loud 85 dB alarm when CO reaches dangerous levels. Most states now require CO detectors in residential buildings. If your CO alarm sounds, the CDC's guidance is clear: get outside immediately, call 911, and do not re-enter until emergency services confirm it is safe.
The combination smoke and CO alarm is a popular choice that covers two critical threats in one device. Placement near sleeping areas is essential — the alarm needs to wake you up.
Do You Need Both?
Short answer: Yes. In most homes, both are needed.
These detectors address completely different hazards with different sensor technologies. A CO detector cannot detect radon. A radon detector cannot detect CO. Having one does not protect you from the other.
If forced to prioritize on a tight budget: a CO detector is the more urgent purchase because CO can kill within minutes. But radon testing should follow as soon as possible — a $15 short-term radon test kit is a small price to rule out the second leading cause of lung cancer.
Most homeowners who test their homes discover at least one air quality surprise. The peace of mind from knowing — rather than guessing — is worth more than the cost of both devices combined.
Recommended Detectors
Airthings Corentium Radon Detector
Continuous digital radon monitoring. No lab required — read results directly on the display. Battery-powered with 2-year life. The EPA recommends testing every home.
Check Price on Amazon →
Kidde Carbon Monoxide Detector
Electrochemical sensor with 85 dB alarm. Battery-operated — works during power outages. The CDC recommends CO detectors on every level of your home.
Check Price on Amazon →
The wrong choice costs more than the detector
Combination Smoke + CO Alarm — One Device, Two Threats Covered
Most families who experienced CO poisoning never thought it would happen to them. A combination alarm covers two of the three most deadly home hazards in a single device. Placed near bedrooms, it provides the protection that matters most — waking you up when danger is present.
Get the Combination Alarm — Cover Both Threats →Budget-Friendly Option: Start With a Radon Test Kit
Not ready for a continuous radon monitor? A short-term radon test kit gives you a snapshot reading for under $20. The First Alert Radon Gas Test Kit is EPA-listed and includes lab analysis. Place it in your lowest living area for 2–7 days, mail it in, and get results. If levels are high, you can then invest in continuous monitoring or mitigation.
Get the Radon Test Kit — ~$15 First Step →Browse Top-Rated Radon Test Kits
Compare short-term and long-term radon testing options on Amazon
See All Options →Browse Top-Rated CO Detectors
Compare plug-in, battery, and combination CO detectors on Amazon
See All Options →Frequently Asked Questions
Can one device detect both radon and carbon monoxide?
No. Radon and CO are fundamentally different hazards requiring different sensor technologies. Radon is detected via alpha-particle ionization or charcoal absorption, while CO uses electrochemical sensors. You need separate devices for each threat.
Which is more dangerous — radon or carbon monoxide?
Both are deadly but in different ways. Carbon monoxide kills quickly — CO poisoning can be fatal within minutes at high concentrations. Radon kills slowly — it is the second leading cause of lung cancer after smoking, responsible for about 21,000 deaths per year in the US according to the EPA. Both require detection.
Where should I place a radon detector vs a CO detector?
Radon detectors go in the lowest lived-in level of your home (basement or ground floor), at least 20 inches off the floor and away from drafts. CO detectors go on each floor, especially near sleeping areas and near fuel-burning appliances, at breathing height on walls.
Do I really need both if my home is new?
Yes. New construction can actually have tighter building envelopes that trap radon indoors. And any home with gas appliances, a fireplace, or an attached garage is at risk for CO. The EPA recommends every home test for radon regardless of age, and the CDC recommends CO detectors on every level.
Your home's air is not guaranteed safe until you test it.
Most families who discover radon or CO in their homes wish they had tested sooner. A radon test kit and a CO detector together cost less than dinner out — and provide protection that lasts for years.