Updated October 27, 2026
Clocks fall back one hour at 2 a.m. on Sunday, November 1. Make it the day you swap the battery in every carbon monoxide alarm in the house, and then book the furnace’s fall look while it’s on your mind: in Northern Virginia the $67 Heating Check runs through December 31.
The alarm and the furnace check are two different jobs. The alarm tells you carbon monoxide is already in the air. The yearly check is someone looking at the equipment that burns gas in your basement. You want both, and here’s why, from the people who write the rules.
The ten-minute carbon monoxide detector routine for clock-change weekend
Do these in order, alarm by alarm. Bring a step stool and a pack of the batteries your alarms take.
- Swap the battery. Every battery-powered alarm, and every plug-in or wired one with a battery backup. If it’s a sealed unit with no battery door, skip to step three.
- Press the test button. It should sound. Just know what that proves (next section).
- Read the date on the back. Every carbon monoxide alarm has a recommended replacement age, and the Consumer Product Safety Commission says to get it from the manual or the manufacturer. If the alarm is past it, replace the alarm, not just the battery.
- Count them. CPSC wants one on every level of the home and outside the sleeping areas, with battery backup. Interconnected alarms are best, because when one sounds, they all sound.
- Check where they sit. Not behind furniture or curtains, not right by a heating vent, not in the kitchen and not above a gas appliance. Those are CPSC’s spots to avoid.
- Book the furnace. That’s the part the alarm can’t do for you, and it’s the rest of this post.
Less than most people think. CPSC puts it plainly: the test button checks whether the alarm’s circuitry works, not the accuracy of the sensor. A beep means the speaker, the battery and the board are alive. It doesn’t tell you the sensor would catch carbon monoxide at the level it’s supposed to.
That’s why the date on the back matters more than the beep. Sensors age out, and the manufacturer’s replacement age is the only real clock on that. Follow the manufacturer’s own testing instructions too; CPSC points you there first.
$598 Whole Home Air Duct Cleaning
Every supply and every return line in the house, register covers off, washed and put back, for $598 instead of $798. See the price
Why the alarm waits before it sounds
A carbon monoxide alarm isn’t built to go off at the first trace. The standard to look for on the box is UL 2034 (CPSC says to buy an alarm that meets it), developed with input from CPSC, and it sets how long an alarm may take to sound at each level. First Alert’s summary of the standard lays them out:
| Carbon monoxide in the air | The alarm has to sound within |
|---|---|
| 70 ppm (parts per million) | 60 to 240 minutes |
| 150 ppm | 10 to 50 minutes |
| 400 ppm | 4 to 15 minutes |
That delay is on purpose. The standard is written to warn you before exposure becomes life-threatening while cutting the false alarms that low, harmless levels would set off. And 70 ppm is the lowest level where the alarm has to sound at all. So a small, steady amount can sit under the alarm’s line for hours, and the alarm is doing exactly what it was designed to do. It’s the backstop. The furnace is the thing to look after.
Carbon monoxide can feel like the flu
CPSC lists the early signs of low to moderate exposure as flu-like, but without the fever: headache, fatigue, shortness of breath, nausea and dizziness. That overlap is easy to miss in November, when half the house has a cold anyway.
In one small emergency department study from the 1980s, researchers drew blood from patients who came in with flu-like symptoms over one winter month. Of the 55 who took part, 13 had carbon monoxide levels the study counted as exposure, and the doctors treating them hadn’t diagnosed any of them with it. The study didn’t trace those cases to furnaces. What it shows is how easily carbon monoxide hides behind symptoms everyone already expects in winter.
CPSC’s advice if you feel those symptoms and suspect carbon monoxide, alarm or no alarm: get outside to fresh air right away, call the fire department from a neighbor’s home, and tell a doctor you think it was carbon monoxide. If an alarm sounds, don’t go looking for the source. Get everyone out, call 911, and don’t go back in until responders say so. Our post on what to do when a carbon monoxide alarm goes off walks through it step by step.
What happened in Woodbridge in December 2023
This isn’t a far-off statistic. In December 2023, Prince William County Fire and Rescue crews went to a home on Neabsco Creek Court in Woodbridge, and ten people, five adults and five children, went to the hospital. Building officials said the carbon monoxide came from a broken furnace pipe in the basement (Patch, December 15, 2023).
Their advice afterward was the same advice this post gives: “All gas fired appliances and furnaces need regular inspection for proper operation.”
Then get the furnace looked at before the cold settles in
CPSC’s own list is short: have the heating system professionally inspected and serviced every year, and have the inspector look at chimneys and flues for blockages, corrosion and loose or disconnected joints. Its line on alarms is the one to remember: an alarm can add some protection, but it’s no substitute for proper use and upkeep of the appliances that make carbon monoxide.
That yearly look is what the $67 Heating Check is for, on one furnace or heat pump, through December 31. On a gas furnace the technician inspects the burners, igniter, flame sensor and heat exchanger, tests the electrical parts, checks the thermostat, and measures airflow and temperature rise. Anything that needs attention gets photographed and written down before we leave, so you see what we saw. While the technician is there, ask them to point out the furnace’s vent pipe, where it runs to the wall or chimney, so you know what it should look like.
One thing the check isn’t: a replacement for the alarms. Keep both. If you’d rather see every deal we’re running this fall, they’re on the offers page. And if the furnace hasn’t run yet this season, our first cold night test run is a good ten minutes to spend before you call.
Carbon monoxide detector questions
When does daylight saving time end in 2026?
Sunday, November 1, 2026, at 2 a.m., when clocks go back one hour. It’s an easy weekend to remember the carbon monoxide alarm batteries.
Should I change carbon monoxide detector batteries when the clocks change?
Yes. It’s a reminder you already get twice a year. Swap the battery in every battery-powered alarm and every backup battery, press the test button, and read the replacement date on the back while you’re up there.
It means the circuitry works. The Consumer Product Safety Commission says the test button checks the circuit, not the accuracy of the sensor. That’s why the alarm’s replacement age, from the manual or the manufacturer, matters too.
Where should a carbon monoxide detector go?
CPSC says on every level of the home and outside the sleeping areas, with battery backup, interconnected if you can. Keep them away from heating vents, out of the kitchen, not above gas appliances and not where furniture or curtains cover them.
When should I replace a carbon monoxide detector?
When it reaches the replacement age the manufacturer gives, which is on the alarm or in its manual. A new battery doesn’t reset an old sensor.
How long does a carbon monoxide detector take to go off?
It depends on the level. Under the UL 2034 standard, an alarm must sound within 60 to 240 minutes at 70 ppm, 10 to 50 minutes at 150 ppm, and 4 to 15 minutes at 400 ppm. Below 70 ppm it isn’t required to sound.
Can carbon monoxide feel like the flu?
Yes. CPSC describes the early signs of low to moderate exposure as flu-like, without the fever: headache, fatigue, shortness of breath, nausea and dizziness. If you suspect it, get outside to fresh air and call the fire department from a neighbor’s home.
Is a carbon monoxide detector enough, or do I still need a furnace check?
You need both. CPSC recommends a professional inspection and service of the heating system every year and says an alarm is no substitute for upkeep. In Northern Virginia, the $67 Heating Check covers one furnace or heat pump through December 31.
Book the Heating Check while the clocks are fresh in your mind
Swap the batteries Sunday, read the dates on the backs, and then get the furnace looked at. Book the $67 Heating Check online, use the form at the top of this page, or call (703) 997-9757. It runs through December 31. Want the bigger picture on fall visits? Here’s what a furnace tune-up costs in Northern Virginia and the full HVAC service checklist.
SwiftPro Heating, Cooling & Plumbing services, repairs and installs furnaces, heat pumps, air conditioners, ductless mini splits and hot water boilers across Northern Virginia from Chantilly and Ashburn, with a dedicated HVAC team and a separate plumbing team. Family owned, BBB Accredited with an A rating, 24/7 emergency service, Virginia Class A contractor license 2705192276, and rated 5.0 stars across 1,130 reviews on Google, Angi, Yelp, the BBB and Facebook. Read the reviews.
