Quick disclaimer before we dive in: I am NOT a carbon monoxide expert, HVAC professional, or scientist (my high school teachers can back me up on this one). I’m a homeowner and a real estate agent who cares deeply about the families living inside the homes I help buy and sell. Everything below is based on personal experience, research, and publicly available safety information. Please always consult qualified professionals for your specific situation
Okay. Let’s talk about something that gave me chills.
A friend of mine recently shared a story (no names, no details for privacy) about their family feeling completely “off” for weeks. Headaches. Brain fog. Nausea. Emotional changes that felt wildly out of character. They thought maybe it was stress. Or the flu. Or seasonal depression.
It turned out to be carbon monoxide exposure in their home.
Then — as if that wasn’t enough — I read another story from a homeowner who moved into a new house and started feeling strange. Six weeks later they finally left the house and called 911. The shocking part? Their carbon monoxide detector never went off, even though it chirped when tested, the green light was on, and appeared to be working just fine.
Winter homes. Closed windows. Fireplaces running. Furnaces working overtime.
It felt important to write about this, even though this winter in Colorado feels a lot more like spring (our snow is coming - I can feel it!).
What Is Carbon Monoxide — and Why Is It So Dangerous?
Carbon monoxide (CO) is a colorless, odorless, tasteless gas created when fuel doesn’t burn completely. You cannot see it. You cannot smell it. You cannot taste it.
That’s why it’s often called “the silent killer.”
It builds up indoors when fuel-burning appliances malfunction, aren’t vented properly, or are repaired incorrectly.
How Common Is Carbon Monoxide Poisoning?
In the United States each year:
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More than 100,000 people visit emergency rooms due to carbon monoxide exposure.
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Hundreds of people die annually from accidental CO poisoning.
Most of these cases happen inside homes. And winter months see a significant spike.
This is not rare. It’s not dramatic. It’s not “one in a million.”
It’s preventable.
Common Household Sources of Carbon Monoxide
Many everyday household systems can produce carbon monoxide if something goes wrong:
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Gas fireplaces
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Furnaces and boilers
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Gas stoves and ovens
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Water heaters
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Gas dryers
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Attached garages (running cars, snowblowers, etc.)
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Portable generators or space heaters
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Improper DIY repairs or aging equipment
And newer homes are not immune. Even “cozy ambiance” fireplaces can become dangerous if something malfunctions.
Symptoms of Carbon Monoxide Poisoning
Here’s where it gets tricky — because symptoms often mimic the flu, burnout, or seasonal blues.
Early symptoms:
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Headache
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Fatigue
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Dizziness
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Nausea
Moderate symptoms:
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Confusion or brain fog
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Irritability or mood changes
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Trouble concentrating
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Depression-like symptoms
Severe symptoms:
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Vomiting
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Chest pain
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Loss of consciousness
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Neurological effects
Children and people working from home may experience symptoms first simply because they spend more time indoors.
Can a Doctor Test for Carbon Monoxide Exposure?
Yes — and this is important.
Doctors can perform a blood test that measures carboxyhemoglobin (COHb) levels. This shows how much carbon monoxide is bound to your red blood cells. Some emergency departments also use CO-oximetry for quicker detection.
Timing matters. Carbon monoxide leaves the bloodstream over time, so testing is most accurate during or shortly after exposure.
If you ever suspect something isn’t right, it’s critical to mention possible carbon monoxide exposure specifically.
Carbon Monoxide Detectors: What Homeowners Should Know
This is where things get really interesting.
Most standard carbon monoxide detectors sold at big-box stores meet national safety standards. That’s good. They are absolutely better than not having one at all.
But here’s something many homeowners don’t realize:
Most residential CO detectors are designed to alarm based on time + concentration, not instantly at the first trace of carbon monoxide.
For example, many UL-listed detectors may not alarm until carbon monoxide reaches around 70 parts per million (ppm) for a sustained period of time. This is intentional — it reduces false alarms.
However, that also means lower-level exposure could potentially cause symptoms before the alarm triggers.
That doesn’t mean standard detectors are “bad.” It just means understanding how they work is important.
How to Choose a Higher-Quality or More Sensitive Detector
If you want added peace of mind, here are features to look for:
1. A Digital Display
A detector that shows real-time ppm levels is incredibly helpful. You can see rising levels before they reach emergency thresholds.
2. UL or CSA Certification
Always verify independent certification. Accuracy matters more than marketing claims.
3. Electrochemical Sensors
These are considered the gold standard. They are generally more accurate and less prone to false alarms.
4. Battery Backup
Whether plug-in or hardwired, battery backup is critical during power outages — when heating systems are often running hardest.
5. Check the Expiration Date
Most CO detectors last 5–10 years. The manufacture date should be printed on the back. And I always recommend new homeowners just replace all of the CO detectors in the house - it's a small price to pay for your family's health and safety.
What About Detectors That Alert Earlier or Detect Gas Leaks?
There are newer products on the market that advertise:
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Lower-level CO detection
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Immediate alerts
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Dual detection (carbon monoxide + natural gas)
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Real-time monitoring
Some homeowners prefer these for added layers of protection — especially in homes with multiple gas appliances or fireplaces.
If exploring these options:
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Make sure they are independently certified.
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Understand that “alerts immediately” doesn’t mean alarming at zero ppm — extremely low readings are not always dangerous.
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Prioritize reliable sensors over flashy marketing.
More data can be helpful. But proper installation and maintenance matter just as much.
Colorado Requirements
In Colorado, carbon monoxide detectors are required in homes that have fuel-burning appliances and/or attached garages. They are typically required:
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On each level of the home
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Within 15 feet of all sleeping areas
These often come up during inspections and final walkthroughs in real estate transactions — and for good reason.
What To Do If a CO Alarm Goes Off
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Get everyone — including pets — outside immediately.
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Call 911 or your local fire department.
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Do not re-enter the home until professionals say it’s safe.
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Contact a licensed HVAC professional or your gas company.
Do not ignore it. Do not assume it’s “probably nothing.”
Why This Matters in Real Estate
As a real estate agent, I see fireplaces, furnaces, water heaters, and gas appliances every single week.
Home inspections catch many issues — but not all of them.
Proper maintenance. Professional repairs (not DIY fixes). Functioning detectors. Replacing units before end-of-life.
These aren’t small details. They protect the people living inside the home.
Final Thought
If this post does one thing, I hope it simply gets your wheels turning.
Test your detectors. Check the expiration date. Schedule maintenance. Trust your instincts if something feels off.
Carbon monoxide poisoning is serious.
But it’s also preventable.
And if you ever have questions about your home — safety items included — I’m always happy to be a resource.
*This post is based on my personal experiences, homeowner research, and publicly available safety information. I am not a carbon monoxide specialist, medical professional, or certified safety expert. Please consult licensed professionals and do your own research when making safety decisions for your home. My goal here is simply awareness and education.