My CO Alarm Sat Green for Three Years. The Air Was at 42 PPM.

A reader's six-week investigation into the white plastic box on her ceiling — and the federal standard that allowed it to stay quiet.

I trusted my CO alarm for three years. The whole time, it was lying to me.

The alarm on my ceiling never made a sound. Three years it sat up there, blinking green like a little night light, and the whole time I was breathing poison in my own kitchen.

HVAC Joe walked in carrying a yellow plastic handheld meter. The meter started beeping like a microwave that's done. Fast, sharp, every half-second. He held it out and the screen said 42. My detector blinked green on the ceiling. Three years of green. The button means nothing.

What follows is what I learned over the next six weeks. I am writing it down for the next woman with a green light on her ceiling.

For six weeks, I thought I had the flu.

I bought soup. I bought tissues. I sat on the couch wrapped in Roy's old robe and watched HGTV with a heating pad on my forehead, wondering why I couldn't shake it.

The headaches came every afternoon around three, like a train you can set your watch by. Behind the eyes. Up the back of my neck. I took Tylenol like it was candy. I would forget what room I walked into. Mid-step. My daughter Beth said, "Mom, you sound drunk on the phone." I wasn't drinking. I hadn't had a glass of wine in a month.

I went to Dr. Patel twice. First visit, a low-grade virus. Second, my thyroid. The bloodwork came back fine. He never asked about my furnace.

Riley wouldn't go downstairs. He'd plant himself at the top of the basement stairs and look at me. Just look. He is a beagle — he is nose-first about everything — and he wouldn't go near that door. Beth made me call the HVAC company.

Riley knew. The dog knew before I did. The night Joe left, I drove Riley through a McDonald's and ordered him a McDouble in the front seat of the Buick. He ate it on the passenger side with the wrapper in his paws. I told him he could have one a week for the rest of his life.

What Joe told me, standing in my kitchen.

Joe is an independent contractor. About fifty. Drops his g's a little. No condescension. He set the yellow meter on my counter and explained the part that made me angriest.

The test button on a standard CO alarm only tests the speaker. Not the sensor. The part inside the box that is supposed to read the air — it is not in the test loop. The button confirms the buzzer can buzz. The button does not confirm the sensor can sense. A detector with a completely dead sensor will still pass its own test, every time.

Then he opened his phone and showed me a Kidde service bulletin. Kidde — the company whose alarm was on my ceiling. Their own words:

"Even if the test button works fine, the sensor inside may not be as effective."

The button worked. The button always worked. The button means nothing.

The rule book the alarm was built to obey.

Joe pulled up the Structure Tech home-inspection article next. Reuben Saltzman, a home inspector in Minneapolis, has been writing about this for fifteen years. Joe read the line aloud, slowly, so I could write it down:

"The Underwriters Laboratory standard UL 2034 requires carbon monoxide alarms not to sound off when exposed to carbon monoxide levels under 30 parts per million."

UL 2034 is the federal standard governing the cheap CO alarms at every hardware store in America. It is on the back of mine. It is on the back of yours.

Read that top row twice. The unit is designed not to alarm when exposed to a constant level of 30 PPM for 30 days. That is not a defect. That is how it is supposed to behave. Now put that against what the regulators say about safe air.

Firefighters evacuate a building at 35 PPM. NIOSH evacuates workers at 35 PPM. My residential alarm was legally permitted to ignore 30 PPM for thirty consecutive days. Do the subtraction.

The standard was not written to keep your air safe. It was written to keep alarms quiet. 412 Fire Safety says so in plain language: "If alarms activated at very low levels: People would experience frequent false alarms. Devices would be unplugged. Families would lose protection." The threshold is a commercial compromise. It exists so you do not unplug the unit while you cook. Standard alarms are, as the industry phrases it, programmed to ignore.

I felt like a fool. Sixty-four years old, raised three kids, ran a household for forty-one years, and I trusted a piece of white plastic on the ceiling because the manual said push the button once a month.

What 42 PPM looked like in my house.

Most residential water heaters put out 25 to 50 PPM on a bad combustion day. Mine was running on the high end, drifting up through the basement door and pooling in the living room where I sat every afternoon with the heating pad. The alarm upstairs was, by design, deaf to that range.

The Indoor Doctor case file describes a family in nearly the same configuration: "chronic headaches and fatigue for months… Testing revealed low but unhealthy levels of carbon monoxide near their gas fireplace and furnace, even though their CO detectors never went off." That was me. That was my Dr. Patel visits. That was my six weeks on the couch. The CPSC, in 2021, filed an administrative complaint citing 24,000 CO detectors that had failed to alarm. The legal phrase is knew or should have known.

What I put on my counter instead.

Joe shut my gas off, called the utility, and gave me a list. Get a unit with a screen. Get a unit that shows the air. Get a unit that does not require you to trust a light.

I bought Alveo. Three of them. One in the hallway. One in the kitchen. One near the furnace. The first thing I noticed is that the screen is on. Not a light. A screen. Four live numbers on one backlit LCD: temperature in °F at the top with a thermometer icon, CO concentration in PPM, combustible gas as %LEL (the percent-of-lower-explosive-limit reading, which catches natural gas and propane), and humidity as %RH at the bottom. Four signals. One screen. Real digits. No green light pretending.

Underneath the screen, three labeled lights. POWER (green, on when the unit has power). ALARM (red, on in an alarm state). And the one Roy's alarm never had — FAULT (amber, on when the sensor itself reports a self-check failure). My old alarm had a single green LED that meant one thing: "I have power." Alveo separates "power present" from "alarm condition" from "the sensor itself is wrong." Three legible states instead of one ambiguous one.

Alveo calls the sensing system ForeWatch™. Joe had explained the principle that morning standing in my kitchen, before he left to pull the permit. The cheap alarms are built around a single threshold — one number, one moment, one binary. The system in this device was built around the curve. It watches the slow rise the threshold is permitted to ignore. The screen sits at zero when the air is clean. The number goes up when something is rising. It alerts before 30 PPM — below the line where the standard units are allowed to stay quiet. Three gases on one device: carbon monoxide, natural gas, and propane. No batteries. No Wi-Fi. No app.

Now I check the four digits before coffee. Zero. Zero. Zero. Zero. Zeros across the board. That's all I need to see.

The detector Roy mounted on that ceiling in '96 cost twenty-nine dollars at the hardware store. The replacement cost me $43.16 per unit, and there are three of them in the house now. I am paying more for the better device. The difference is the price of being told the truth about the air I am breathing.

The woman who reads the air now.

For six weeks I thought I had the flu. Now I know I had 42 PPM in my living room and a 25-to-50 baseline drifting up out of the basement off the water heater. I know what UL 2034 permits. I know what NIOSH evacuates at. I know that the test button on a standard CO alarm tests the speaker, not the sensor. I know that the people who made the box on my ceiling knew, or should have known, what kind of leak it was built to miss.

"I check four numbers now, before coffee. Zero. Zero. Zero. Zero. Beth has one on her counter. She texts me her numbers. My sister in Akron got one. The woman next to me at church got one. I'm not going back to a green light. Neither are they."

I will never again — never — trust a thing on a ceiling that tells me everything is fine without giving me a number. I need a number. I need to see a number. Green is not a number. Green is a lie.

What it costs, against what it could have cost.

I paid $129.49 for the Alveo 3-Pack — $43.16 per detector. Strikethrough on their site was $299.85. FREE Shipping over $60. Less than 1 in 100 customers ask for a refund. Every Alveo detector ships with a 100-day risk-free trial and a 3-year warranty. If it doesn't earn its spot in your home, send it back — return shipping covered.

If the only thing on your detector is a light, you do not know what is in your air. You know what is in the circuit that powers the light.

That's two different things.

— Carolyn Henderson 💛
Reader Investigation, Columbus, Ohio
P.S. I unplugged the old Kidde. It went in the trash. Beth has the new one on her kitchen counter now — she texts me the morning numbers. *See footer for editorial disclosures.