The plug-in with display
First Alert CO615
Plugs into an outlet, keeps a battery backup and shows the CO level in ppm, which turns a mystery beep into information.
Gear guide · Air · updated October 12, 2026
Carbon monoxide alarms
If your home burns gas, oil, propane or wood, or has an attached garage, CO alarms are the last line of defense behind yearly appliance servicing and an energy auditor's combustion safety test. CPSC recommends alarms on every level and outside sleeping areas, ideally interconnected so that when one sounds, they all sound. Many states require them in homes with fuel-burning appliances or attached garages; some apply the rule only at sale, in rentals or in new construction.
Not sure this category applies to your home? The testing guide covers which tests matter. For the testing side, see the carbon monoxide guide and combustion safety testing.
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The other benchmark
Kidde Nighthawk (digital display)
Kidde's long-running equivalent: plug-in power, battery backup, a digital readout and a peak-level memory button that shows what happened while you were out.
The two-in-one
First Alert combination smoke + CO
If a smoke alarm is due for replacement anyway, a combination unit covers both jobs from one ceiling spot. Check that the box lists UL 217 for smoke and UL 2034 for carbon monoxide.
Before you buy
- Look for UL 2034 on the package. It's the US standard CO alarms are tested to (Edition 5, revised in 2024), and CPSC says to install alarms that meet the current edition.
- Placement, per CPSC: every level and outside sleeping areas, away from heating vents and anywhere furniture or drapes could cover them. CPSC does not recommend kitchens or spots right above fuel-burning appliances.
- The test button checks the circuitry, not the sensor. Replace alarms at the age given in the product literature; CPSC sets no fixed number of years, so note the date on the back.
- State rules differ. Some states require alarms in every home with a CO source, others only at sale, in rentals or in new construction, so check yours.
- An alarm is the backstop, not the fix: yearly servicing of fuel-burning appliances and the auditor's combustion safety test come first.
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Measure, then act
Gear tells you what is happening; an energy audit tells you why. A certified auditor measures air leakage, insulation and combustion safety, and can tell you which of these categories matter in your home.
Also in gear guides: Radon monitors & test kits · Indoor air quality monitors · Air purifiers (HEPA)