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Carbon monoxide (CO) is an invisible, odorless gas that can be dangerous even at low levels over time. Because you can’t see or smell it, the only reliable way to know it’s present is to use a carbon monoxide alarm. This page explains what CO is, where it comes from, what a CO detector actually detects, and how to decide if your home should have CO alarms.
What Is Carbon Monoxide?
Carbon monoxide is produced when fuels don’t burn completely. It can build up indoors if exhaust can’t escape properly or if equipment is damaged, blocked, or used incorrectly. CO can spread through a home and reach sleeping areas, which is why alarms are so important.
Why CO is dangerous
CO can prevent your body from using oxygen effectively.
People may not realize they’re being exposed because early symptoms can feel like everyday illness or fatigue.
CO exposure can affect anyone, including pets, and it can be especially dangerous while sleeping.
What Does a Carbon Monoxide Detector Do?
A carbon monoxide alarm monitors the air for elevated CO levels. If the alarm senses a dangerous concentration based on its internal safety thresholds, it sounds an alert so you can take action quickly.
What you can expect from a CO alarm
Continuous monitoring: it checks air over time, not just a single moment.
Audible alarm: loud alert designed to be heard from nearby areas.
Status indicators: many alarms include lights or display indicators that show power, alarm, or fault status (varies by model).
Test/Silence button: used to confirm operation and silence certain alerts (follow your model’s instructions).
What a CO alarm does not do
It does not remove carbon monoxide from the air.
It does not replace proper ventilation or appliance maintenance.
It does not prevent CO from being produced; it provides warning when CO levels become dangerous.
Where Does Carbon Monoxide Come From?
CO can be produced by common household sources that burn fuel. Problems usually occur when exhaust is blocked, equipment is malfunctioning, or a device is used in a way it wasn’t intended.
Common CO sources in and around a home
Furnaces, boilers, and water heaters
Fireplaces and wood stoves
Gas stoves, ovens, and space heaters
Portable generators (especially when used in or near the home)
Grills or other outdoor cooking equipment used indoors
Car or truck exhaust from attached garages (even with the garage door open)
Does a Carbon Monoxide Detector Detect Natural Gas?
In most cases, no. A standard carbon monoxide alarm is designed to detect carbon monoxide gas, not natural gas (methane) or propane. Natural gas detectors use different sensor technology and are made specifically to detect fuel-gas leaks.
CO vs natural gas: quick difference
Carbon monoxide: a toxic gas produced by incomplete combustion (danger is poisoning).
Natural gas (methane) / propane: a fuel gas that can leak (danger is fire/explosion and oxygen displacement in some cases).
If you are concerned about both risks, look for the right alarm type for each hazard, or a combination solution only if it specifically lists the gases it detects.
Do I Need a Carbon Monoxide Detector in My Home?
Many homes benefit from CO alarms, especially if there is any chance CO could be produced or enter the home. Even all-electric homes may be exposed if they share walls with other units, have attached garages nearby, or have fireplaces or other combustion sources.
You should strongly consider CO alarms if you have
Any fuel-burning appliance (gas, oil, wood, or pellet)
An attached garage
A fireplace or wood stove
A multi-unit living situation (apartment, condo, townhouse) where a neighboring unit could be a source
Any regularly used backup heat source or generator (even if used outdoors)
Quick guidance on how many and where
Install CO alarms outside each sleeping area.
Install CO alarms on every level of the home, including basements.
CO alarms do not need to be near the floor; follow your model’s mounting instructions.
Signs of Carbon Monoxide Exposure
If you suspect CO exposure, treat it seriously. Symptoms can vary, and people may experience them differently.
Headache
Dizziness
Nausea or vomiting
Shortness of breath
Confusion or unusual tiredness
Important: If your CO alarm sounds or anyone feels symptoms, move to fresh air and get help immediately.
Basic CO Alarm Care and Maintenance
Test regularly: many households test monthly using the Test/Silence button.
Power check: replace batteries as needed and confirm the alarm is receiving power (varies by model).
Keep it clean: gently remove dust buildup according to the manufacturer instructions.
Replace on schedule: CO alarms have a limited service life; replace the unit when it reaches end-of-life.
FAQs
What does a carbon monoxide detector actually detect?
It detects elevated carbon monoxide levels in the air over time. If the level becomes dangerous based on the alarm’s safety thresholds, it sounds an audible alert.
Will a CO detector detect a natural gas leak?
Usually no. Standard CO alarms are designed to detect carbon monoxide, not natural gas (methane) or propane. For fuel-gas leaks, use a detector that specifically lists natural gas or propane detection.
Where does carbon monoxide come from in a home?
CO can come from fuel-burning appliances (furnace, water heater, fireplace), car exhaust from attached garages, or equipment like generators or grills used improperly. CO risks increase if exhaust is blocked or equipment malfunctions.
Do I need a CO detector if my home is all-electric?
Many people still choose CO alarms, especially in multi-unit buildings or if there’s an attached garage nearby. CO can enter from adjacent spaces even if you don’t have fuel-burning appliances in your unit.
What should I do if my carbon monoxide alarm goes off?
Move everyone to fresh air immediately and call emergency services from outside. Do not re-enter the home until professionals say it’s safe.
Ensure your home is protected with our First Alert smoke alarm installation guide. Learn the best placement for every room, understand NFPA recommendations, and avoid dead air zones to keep your family safe.
Learn where to install smoke alarms on every level and near bedrooms, plus where not to place them. Avoid “dead air” corners, vents, and ceiling fans for reliable detection.
Learn the differences between hardwired and battery smoke alarms and how to install each type. Includes wiring basics, placement tips, and when to choose each option.
Learn how to interconnect multiple smoke alarms so all units sound together. Covers hardwired interconnect, wireless options, compatibility tips, and troubleshooting.
Learn when to replace your First Alert smoke alarm, how to identify your connection type, choose the right replacement, install it safely, and dispose of old alarms responsibly.
Learn smoke alarm placement rules for apartments and rental homes, who is typically responsible for installation and upkeep, and hardwired vs battery options. Non-legal code basics included.
Learn where to install carbon monoxide alarms, how many you need, and placement tips for houses, apartments, and rentals - plus what to do when an alarm sounds.
Learn where to place carbon monoxide detectors for best protection - every level, near sleeping areas, and the right distance from appliances. CO alarms don’t need to be near the floor.
Compare hardwired, battery, and plug-in carbon monoxide alarms and follow simple installation steps for each type, plus placement tips, safety notes, and FAQs.
Learn what carbon monoxide is, where it comes from, what CO detectors detect (and don’t), whether they detect natural gas, and how to know if your home needs CO alarms.
Learn when to replace your First Alert carbon monoxide alarm, how to swap battery, plug-in, or hardwired models step-by-step, choose the right replacement, and dispose safely.
Learn CO detector placement for apartments and rental homes, who typically handles installation and battery changes, hardwired vs battery vs plug-in options, and basic code concepts (non-legal advice).
Learn how often to test smoke and CO alarms, how to test step-by-step, what to do if a test fails, how to reset First Alert alarms, and how monthly cleaning helps prevent false alarms.
Learn how often to test smoke alarms, how to test them step by step, what the test button checks, what to do if a smoke alarm fails, and common maintenance tips.
Learn how often to test carbon monoxide detectors, how to test them step by step, what the test button checks, what to do if a CO alarm fails, and helpful maintenance tips.
Learn what to do if a smoke alarm or carbon monoxide alarm fails testing, including battery checks, power checks, cleaning, reset steps, and when to replace the unit.
Learn how to reset a First Alert smoke alarm or carbon monoxide alarm step by step, including battery, plug-in, and hardwired models, plus common reasons an alarm needs a reset.
Learn how to clean a smoke alarm step by step, why dust buildup matters, how monthly vacuuming can help reduce nuisance alarms, and common cleaning mistakes to avoid.
Learn why your smoke alarm chirps, what beep patterns mean, how to prevent nuisance alarms, why alarms chirp after battery changes, and when it is time to replace an expired unit.
Learn why your smoke alarm is chirping, what different beep patterns may mean, and how to troubleshoot low battery, end-of-life, power, and sensor-related issues.
Learn why your carbon monoxide alarm is chirping, what different beep patterns may mean, and how to troubleshoot low battery, end-of-life, power, and sensor-related issues.
Learn why smoke alarms go off without visible smoke, what causes nuisance alarms from cooking, steam, humidity, and dust, and how to help prevent false alarms.
Learn why a smoke or carbon monoxide alarm may still chirp after a new battery is installed, including reset steps, battery fit issues, drawer problems, and end-of-life warnings.
Learn how to change a First Alert smoke alarm battery, how battery replacement differs from sealed 10-year battery models, and what to do if the alarm still chirps after replacement.
Learn how to find the manufacture date on a smoke alarm, why smoke alarms expire after 10 years, and why an alarm may need replacement even if it still seems to work.
Learn how to choose the right smoke, carbon monoxide, combo, or smart alarm. Compare sensor types, power options, connectivity, and key safety features.
Learn the basics of home safety, including early smoke and fire detection, carbon monoxide dangers, family fire escape plans, extinguisher use, and emergency escape ladders.
Learn why early smoke and fire detection matters, how smoke alarms provide critical warning time, and what families should know about placement, testing, and maintenance.
Learn what carbon monoxide is, where it comes from, why it is dangerous, common symptoms of CO exposure, and how carbon monoxide alarms help protect your home.
Create a family fire safety plan with a simple checklist covering escape routes, meeting places, smoke alarms, practice drills, and emergency planning for children and adults.
Learn the PASS method for using a fire extinguisher: Pull, Aim, Squeeze, and Sweep. Get step-by-step fire extinguisher tips, safety basics, and common FAQs.
Learn how emergency escape ladders work, how to test and deploy them safely, where to store them, and how they fit into a second-story fire escape plan.
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Carbon Monoxide Alarm Tips
Interconnected Smoke Alarm Tips
Extinguishing Spray Tips
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