The best carbon monoxide detector depends on where you live and what fuel you burn
A carbon monoxide detector is not optional if you have a furnace, water heater, stove, fireplace, or attached garage — all of these produce carbon monoxide as a byproduct of burning fuel. The best detector for your home is one that meets your local building code, covers the square footage you need, and fits your budget. Most homes need a plug-in model in the main living area and a battery-powered backup in the bedroom.
The choice comes down to three things: whether you want hardwired (connected to your electrical system), plug-in (standard outlet), or battery-powered; whether you want a display that shows CO levels or just an alarm; and whether you want a combination smoke and carbon monoxide detector. All detectors sold in the United States must meet UL 2034 standards, which means they will alarm when carbon monoxide reaches dangerous levels.
Key Takeaways
- Hardwired detectors with battery backup are the most reliable option for homes with furnaces or gas appliances, because they run continuously without depending on you to replace batteries.
- Plug-in detectors cost less and work well in apartments or homes where you cannot run wiring, but you must remember to test them monthly and replace batteries if the power goes out.
- A digital display that shows carbon monoxide levels in parts per million (ppm) lets you catch slow leaks before the alarm sounds, but costs more than an alarm-only model.
- Place one detector on every level of your home and one in or near each bedroom, because carbon monoxide spreads through the air and you need to hear it while sleeping.
- Test your detector monthly by pressing the test button for 3 to 5 seconds, and replace the entire unit every 5 to 7 years, not just the batteries.
Hardwired detectors with battery backup: the standard for most homes
If your home has a furnace or gas water heater, a hardwired detector is the safest choice. These plug into your home's electrical system and include a battery that keeps them running if the power goes out. They cost between $40 and $150 depending on whether they include a display and whether they combine smoke and carbon monoxide detection.
The main advantage is that you never have to remember to replace batteries — the detector runs all the time. The main disadvantage is that installation requires running wiring through your walls, which usually means hiring an electrician. If you are building a new home or renovating, this is the time to install hardwired detectors. If your home already has hardwired smoke detectors, you can often replace them with combination units that detect both smoke and carbon monoxide.
Hardwired detectors with a digital display cost more but show you the current carbon monoxide level in parts per million. This matters because it lets you catch a slow leak — say, from a cracked furnace — before the alarm sounds. If you see levels climbing toward 35 ppm over several days, you can call a technician before anyone gets sick.
Plug-in detectors: the practical choice for renters and apartments
A plug-in detector goes into any standard outlet and costs $20 to $80. It is the most common choice for apartments and rental homes because you do not need permission to install it and you can take it with you when you move. Plug-in models run on household current with a battery backup that activates if the power goes out.
The catch is that you must test the battery monthly and replace it when the low-battery light comes on. If your power goes out for more than a few hours, the battery becomes your only power source, and a dead battery means no protection. You also need to remember to plug it in — it does no good sitting in a box in your closet.
Plug-in detectors with a digital display work the same way as hardwired ones: they show you the current carbon monoxide level so you can catch slow leaks. The display is especially useful in apartments where you cannot easily call a technician — you can document the readings and send them to your landlord as proof that something is wrong.
Battery-powered detectors: backup protection for bedrooms
A battery-powered detector costs $15 to $50 and requires no wiring or outlet. It is the right choice for bedrooms, where you need to hear an alarm while sleeping, and as a backup in homes that already have a plug-in or hardwired detector in the main living area.
Battery-powered detectors depend entirely on you to replace the battery once or twice a year. If you forget, you have no protection. They also have a shorter lifespan than plug-in or hardwired models — most last 3 to 5 years instead of 5 to 7 — because the battery drains even when the detector is not alarming. For this reason, do not use a battery-powered detector as your only detector in a home with a furnace or gas appliances.
Battery-powered detectors without a display are the cheapest option and work fine as bedroom backups. If you want a display, expect to pay more and change the battery more often, because the display uses extra power.
Combination smoke and carbon monoxide detectors
A combination detector senses both smoke and carbon monoxide in one unit. These are available in hardwired, plug-in, and battery-powered versions and cost $10 to $30 more than a carbon monoxide-only detector. They are useful if you want to reduce the number of devices on your walls and ceilings.
The downside is that if one sensor fails, you have to replace the entire unit instead of just the failed part. Some people also find it confusing to have one alarm that could be warning about either smoke or carbon monoxide — you have to check the display or manual to know which one triggered. For this reason, many fire safety experts recommend separate detectors in different rooms: smoke detectors in bedrooms and living areas, carbon monoxide detectors near fuel-burning appliances.
Where to place detectors and how to maintain them
Place at least one carbon monoxide detector on every level of your home, including the basement if you have a furnace there. Place one in or near each bedroom so you will hear it while sleeping. Do not place a detector in the kitchen directly above a stove, because cooking produces small amounts of carbon monoxide and can trigger false alarms. Instead, place it 10 to 15 feet away from the stove.
Test your detector every month by pressing and holding the test button for 3 to 5 seconds. The alarm should sound within 10 seconds. If it does not, replace the batteries if it is battery-powered, or call an electrician if it is hardwired. Replace the entire detector every 5 to 7 years, not just the batteries — the sensor degrades over time and stops working reliably.
If your detector alarms, leave your home when ready and call 911 from outside. Do not go back inside to investigate. Carbon monoxide is invisible and odorless, and even a few minutes of exposure can cause serious harm. Once firefighters have checked your home and cleared it, have a technician inspect your furnace, water heater, and any other fuel-burning appliances.
Price and durability: what you actually pay over time
A hardwired detector with battery backup costs $40 to $150 upfront plus installation, which runs $100 to $300 if you hire an electrician. Over 7 years, that is roughly $20 to $65 per year. You replace the backup battery every 1 to 2 years for $5 to $10.
A plug-in detector costs $20 to $80 upfront with no installation fee. You replace the battery every 6 to 12 months for $5 to $10. Over 7 years, that is roughly $10 to $25 per year. If you need multiple detectors for different rooms, the cost adds up faster than hardwired.
A battery-powered detector costs $15 to $50 upfront. You replace the battery every 6 months for $5 to $10, and replace the entire detector every 3 to 5 years. Over 5 years, that is roughly $30 to $50 per year — the most expensive option per year because you replace the whole unit so often.
Frequently Asked Questions
Do I need a carbon monoxide detector if I have an electric furnace?
No. Electric furnaces do not burn fuel, so they do not produce carbon monoxide. You still need a detector if you have a gas stove, gas water heater, fireplace, or attached garage where a car might run. If you are unsure what type of furnace you have, check your utility bills — gas furnaces show a gas charge, electric furnaces show only electricity.
Can I use the same detector for smoke and carbon monoxide?
Yes, combination detectors work well and cost less than buying two separate units. The trade-off is that if the sensor fails, you replace the whole device. Some people prefer separate detectors so they know when ready whether the alarm is for smoke or carbon monoxide.
What should I do if my detector keeps alarming for no reason?
First, make sure you are testing it correctly — the test button should be held for 3 to 5 seconds. If it alarms during normal use, move it away from the kitchen stove, bathroom, or fireplace, because these produce small amounts of carbon monoxide that can trigger false alarms. If it continues to alarm, replace the battery or the entire unit, because the sensor may be failing.
How long does a carbon monoxide detector last?
Most detectors last 5 to 7 years. Battery-powered models last 3 to 5 years because the battery drains even when not alarming. After the expiration date, the sensor degrades and may not detect carbon monoxide reliably. Write the date you install it on the detector with a marker so you remember when to replace it.
Can I install a hardwired detector myself?
If you have electrical experience, you can run the wiring and connect the detector to an existing circuit. If you do not, hire a licensed electrician. Improper wiring can cause a fire or electric shock. Most electricians charge $100 to $300 for the job, depending on how far the detector is from the nearest circuit breaker.