After 30 Years On The Truck I'm Putting This On Paper — What The Chirp Doesn't Tell You.

The test button on a residential CO alarm doesn't test the sensor. It tests the speaker. I sold customers the better ones for thirty years and I had the cheap one over my own wife's bed. I'm sixty-seven. I'm writing this from the kitchen table where my grandson asked me a question I couldn't answer.

I installed gas water heaters for thirty years. My grandson noticed the alarm in my hallway was older than he is.

Thanksgiving. Pie on the table. Mason is twelve. He looks up at the ceiling and asks why the smoke alarm is yellow. I tell him it's been there since before his dad moved out. He thinks about that. Then he says, "But you used to sell people the better ones." Carol laughed. I laughed because she did. I cut my pie. I didn't taste it.

Two in the morning I got up. Slippers. Walked down the hallway. The disc came off the ceiling with two turns. The back was the color of an old kitchen wall. I could read most of the date stamp: REPLACE BY 12/2009. I'd installed it in '99.

I pressed the test button standing there with the cell in my hand. It chirped right on cue. I knew before I pressed it the chirp doesn't mean a damn thing. It tests the speaker. It doesn't test whether the sensor inside is still alive.

What a 30-year HVAC tech is doing standing in his own hallway at 2 a.m.

I retired three years ago. NATE patch on the tool belt still hanging on the basement bench nail. EPA 608. State gas-fitter card. RSES. Thirty years of certifications on the garage wall — and a sixteen-year-expired sensor over the room my wife sleeps in.

I installed the water heater in this house in 1995. Forty-gallon Bradford White, atmospheric vent, brass fittings I sweated myself. The flue is drafting. The burner's clean. But drafting fine on Tuesday doesn't mean drafting fine on Thursday in a storm, and the disc on the ceiling won't catch the difference until the level is bad enough to put Carol on the floor.

I told a couple in Marshalltown in '04 that their alarm was past date. I wrote the date on the back of the new one with a Sharpie. I never wrote a date on my own.

Mason didn't mean anything by it. He was being twelve. He didn't know he'd put a hole through me at the dinner table. It wasn't fear — at my age, fear isn't what gets you. The kid was right and I didn't have an answer.

I stood there and did the arithmetic. A 1999 Walgreens-tier plastic shell — the kind Kidde and First Alert still sell on the Home Depot CO aisle today, same UL 2034 spec, same chemistry inside, same five-year cell. A five-year electrochemical cell, sixteen years past expiry. The horn worked. The horn always works — it's the cheapest part. The sensor — the part that's supposed to know whether Carol is breathing poison — was a chemistry experiment that ran dry around the time Mason was born.

I didn't put it back on the ceiling. I set it on the kitchen counter where Carol would see it. Then I sat down at the table where we'd eaten the pie and did what I should have done in 1999. I started reading.

What the test button actually tests — and why I knew this for thirty years.

I want to say this plainly because I owe it to anyone who's pressed their test button on schedule and gone back to bed. The test button on a residential CO alarm tests the circuitry and the speaker. It does not test the sensor. The California State Fire Marshal puts it verbatim — "the test button on other detectors only tests whether the circuitry is working." NFPA 72 — the standard that governs commercial life-safety work — requires a functional test where CO gas is applied to the unit to verify the sensor responds. Nobody in residential does this. Most homeowners don't know it exists.

That's the test button. It's a speaker check.

Now the sensor. The disc uses an electrochemical cell — a small wet cell with an electrolyte that breaks down over time. Figaro Engineering, who makes the TGS5141 cell that goes into a lot of these units, states a five-to-ten-year life. Mine was twenty-six. That's not a sensor anymore. That's a plastic disc with a battery and a horn.

So you press the button. The horn chirps. Carol hears it from the kitchen and thinks we're covered. I let her think it. For sixteen years past expiry, I let her think it. That's the part I'm not going to let myself say out loud yet.

The spec the alarm was built to — read the way I'd read it to an apprentice.

The standard is called UL 2034. It's on the back of nearly every CO alarm sold in America — including the one I just took down. The thresholds were written in 1992 and they haven't meaningfully moved. Here's what the spec lets a detector do — and not do.

Read those numbers the way a tradesman would. The disc is not failing. The disc is working exactly the way the spec wrote it. Thirty PPM for thirty days and the unit isn't required to say a word. At seventy — enough to give Carol a headache she'd blame on the weather — the unit has between an hour and four hours before it has to alarm. Up to four hours of seventy PPM is not safety. It's a medical event in progress.

Reuben Saltzman, the Structure Tech home inspector, puts it cleanly: "UL listed carbon monoxide alarms will not alert you to low levels of carbon monoxide in your home because they're designed not to." He calls them the last line of defense. Not a real monitor. A backstop.

I'd known all of this for thirty years. I just hadn't applied the rule to myself.

A CO sensor is the wrong sensor for a gas leak.

Here's the second thing the disc wasn't telling Carol. A CO sensor is blind to methane and propane. Those are the fuels in the lines, not the byproducts. The methane leaks in the front before the burn even happens. If you only watch the back end of the appliance, you miss the leak before it becomes a fire.

I had a CO-only disc above my wife's bed in a house with a '95 atmospheric-vent water heater, a gas range Carol refuses to give up, and a furnace the boys at the shop replaced in '18. Three appliances. Three fuel lines. One sensor blind to two of the three risks. Sixteen years.

The unit I'd recommend to a paying customer with a checkbook open is the NSI 3000 — senses CO down to 5 PPM, only sells through certified contractors. Alveo is the residential cousin of that math.

The other thing I wanted was a real number. Not a green LED. The screen is the test. There's nothing to push. That's how I ended up reading the spec sheet for a unit called Alveo.

Four live numbers. Three lights. ForeWatch™ on the front.

I'll describe what's on the unit the way a tradesman would. No marketing voice. Just what the screen does.

Four live numbers on one screen — temperature, CO in PPM, combustible gas as %LEL, and humidity. Not a green light. CO in parts per million. Combustible gas as a percentage of the lower explosive limit — the same %LEL number a combustion analyzer reads. Temperature in °F. Humidity in %RH. All four updating live, at breathing height, in the room where you sleep.

The mechanism Alveo built it around shows the drift. A smoke alarm waits for the scream. A fuel gauge shows the needle. Alveo's the needle. It reads the air the way my Bacharach Fyrite reads a flue — except it's plugged in twenty-four hours a day and Carol doesn't have to know how to work a meter.

That amber FAULT light is the part I would have killed for in 1999. A sensor that admits when it's wrong. Carol's old disc had one light — green — for twenty-six years. The green said the outlet was working. It said nothing about whether the cell behind it was alive. Alveo separates power from alarm from sensor health. Three states, three lights. I was quiet about the missing third light for as long as I was in the trade.

Carbon monoxide, natural gas, and propane on the same screen. No Wi-Fi. No app. Plugs into the wall. Designed to UL 2034 specifications. Runs continuously off the wall, no batteries to forget. Three-year warranty on the sensor.

Someone from the other end of the same hallway.

I'm not the only one who came to this arithmetic. The version I trust most is from the trade that picks up the phone after my trade doesn't.

"I'm not going to be the guy in the paper whose family asks 'Didn't he work in this trade?' That's not going to be me."
— Ed Moreno

That's the arithmetic. I sold the better ones to customers for thirty years and had the white plastic disc above my own wife's bed. The trade has a name for that. It isn't a kind one. Same screen, same hallway, same trade — and I'd had it backwards for the people I should have known to protect first.

What this costs. What I bought.

One Alveo unit is $59.95. About ten dollars more than the disc on the Home Depot shelf today — the same kind I just took down. That one, like every UL 2034 detector on every shelf, is allowed to sit silent at twenty-nine PPM indefinitely. That isn't a defect. That's the standard working as written.

I bought the three-pack. $129.49. That's $43.16 per detector. One for the hallway above the bedroom door. One for the basement near the Bradford White. One for the kitchen because Carol still has the gas range. Three units, three locations, date in Sharpie on the back of each — the install I would have written up for a paying customer in '99 and never wrote up for myself.

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. Less than 1 in 100 customers ask for a refund. That's a real number.

What I should have written on the back in 1999.

If you've ever pressed your test button and felt covered — I'm sorry. The kid was right about mine, and unless your alarm is newer than the one I just took down, he'd be right about yours.

I'm sixty-seven. I should have been the last man on this street with a sensor that was just for show. I sold the better ones to customers for thirty years and had the white plastic disc above my own wife's bed. Carol never asked. I never volunteered.

There's a number on the screen now. It's been reading zero all morning. The disc is still on the counter where I set it. I'm going to write the new install date on the back of the Alveo with the same Sharpie I used to write dates on customers' alarms for thirty years.

I'm not going to be the guy in the paper whose family asks "Didn't he work in this trade?" That's not going to be me.

— Ed Moreno 💛
Retired HVAC · Kentwood, Michigan · Posted 2026-05-14
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