Carbon monoxide detectors warn you when their sensors detect a CO condition that triggers an alarm. Choosing suitable equipment, placing it correctly, and following its testing and replacement instructions all matter. A monitored setup can also send a supported alarm signal to a monitoring center.
This guide covers alarm types, placement, maintenance, and the difference between local alarms, phone notifications, and professional monitoring.
If a Carbon Monoxide Alarm Sounds
Move everyone outside to fresh air immediately, call 911 from outside, and make sure everyone is accounted for. Do not stay inside to locate the source, silence the alarm, or wait for a monitoring call. Do not go back in until emergency responders say it is safe.
If responders identify a malfunctioning appliance, do not use it until a qualified technician has serviced it. If the alarm sounds again after you return, follow the same steps and have a qualified technician inspect your fuel-burning equipment.
If you suspect CO poisoning, get outside and call 911 even if no alarm is sounding. Tell responders about symptoms and possible CO exposure and get prompt medical attention. See the CPSC’s CO emergency guidance.
Key Takeaways
- CO and smoke are different hazards. A smoke-only alarm does not detect CO; a combination unit must be designed for both.
- Plan coverage using current fire-safety guidance, the manufacturer’s instructions, and applicable local requirements.
- Power, interconnection, phone notifications, and professional monitoring are separate features. Check each one.
- Test alarms regularly and replace them at their specified end of life. A working horn or fresh battery does not establish that an expired sensor is reliable.
- Monitored detection is an additional communication path, not a reason to delay getting outside during an alarm.
What Is Carbon Monoxide?
Carbon monoxide is a poisonous gas you cannot see or smell. It can be produced when fuel burns, including in furnaces, fireplaces, gas ranges, portable generators, and vehicle engines. A malfunction, poor venting, or unsafe equipment use can allow it to build up indoors.
The CDC’s CO poisoning guidance explains that symptoms can include headache, dizziness, weakness, upset stomach, vomiting, chest pain, and confusion. People who are asleep or under the influence of alcohol or other substances can die from CO poisoning before they have symptoms. Do not use the absence of symptoms, a smell, or visible smoke to decide that a home is safe.
An alarm is one layer of protection. It does not repair a faulty appliance, clear a blocked vent, or make unsafe generator use acceptable.
How Do CO Detectors Work?
A CO sensor monitors the air around it and the device evaluates the exposure according to its design. Electrochemical sensing is one technology used in residential equipment. An alarm is not necessarily intended to sound for every trace of CO the instant it appears.
Do not interpret an alarm’s response characteristics or a displayed number as a personal “safe waiting time.” If an alarm sounds or exposure is suspected, follow the emergency steps above.
A self-contained CO alarm typically has its own sounder. A system-connected detector communicates with compatible control equipment. Product descriptions sometimes use “alarm” and “detector” loosely, so confirm how the exact device warns occupants and reports a signal.
How to Choose a CO Alarm or Detector
For a self-contained residential CO alarm, check that it meets the current UL 2034 safety standard and is listed by a nationally recognized testing laboratory. For a system-connected detector, confirm the listing required for its intended use and compatible system. Check the product label and manufacturer’s documentation. Check the model’s instructions and local requirements, including whether a combination smoke/CO unit is suitable for the installation. A listing alone does not establish that your complete installation meets every applicable rule.
| Option | What to check | Important limit |
|---|---|---|
| Battery-powered | Battery type, mounting instructions, replacement schedule, and whether the battery is sealed. | Battery life and sensor life are different; do not assume either is ten years. |
| Hardwired | Electrical requirements, backup power, and compatible interconnection. | Use a qualified professional for wiring work. Hardwiring alone does not establish monitoring. |
| Plug-in | Approved outlet location and backup power. | An available outlet is not automatically a suitable alarm location. |
| Connected or monitored | Compatible panel or hub, alert functions, service requirements, and backup communication. | A phone notification and a monitoring-center signal are different capabilities. |
Connected features can be found on devices with different power sources. “Smart” does not necessarily mean direct Wi-Fi, interconnected sounders, or professional monitoring.
Combination Smoke and CO Alarms
A combination unit is designed to detect both hazards. Confirm that the model provides both functions, and learn the signals for each. Follow its smoke-alarm installation instructions as well as applicable requirements; combining sensors does not eliminate the need for adequate coverage.
Interconnection and Accessible Alerts
Compatible interconnected alarms can sound together when one activates. Do not assume different brands or models can be linked. If someone may not hear a standard sounder, ask a qualified fire-safety professional about compatible alerting equipment and an appropriate emergency plan.
Where Should You Place Carbon Monoxide Alarms?
The NFPA’s 2026 educational guidance recommends CO alarms in each room or area used for sleeping, outside separate sleeping areas, and on all levels of the home, including the basement. Follow the specific model’s placement and mounting instructions and confirm applicable local requirements.
| Area or issue | What to plan |
|---|---|
| Sleeping rooms and areas | Plan coverage where people sleep and outside separate sleeping areas, including rooms used occasionally for sleeping. |
| Each level | Account for all floors, including the basement, in the overall coverage plan. |
| Mounting height | Use the device’s approved ceiling, wall, or outlet installation; there is no single height for every model. |
| Appliances, vents, and moisture | Observe the manufacturer’s required clearances and environmental limits. Do not apply a universal appliance distance to every alarm. |
| Furniture and obstructions | Keep the alarm unobstructed and accessible for testing and maintenance. |
CO mixes with room air; do not place an alarm near the floor simply because you think the gas will sink there. For a difficult layout, ask a qualified installer or your local fire department for placement guidance.
Testing and Maintenance
Test CO alarms at least monthly and follow the model’s instructions. For a monitored system, use the provider’s testing procedure so the monitoring center knows a test is taking place. Restore normal monitoring afterward.
The CPSC explains that a test button checks circuitry, not the sensor’s accuracy. A successful button test does not prove there is no CO in the home or extend the device’s service life.
- Use only the specified replacement battery, where replacement is permitted.
- Do not open a sealed-battery alarm to replace its battery; follow its replacement instructions.
- Follow the manufacturer’s cleaning guidance and keep the sensing openings unobstructed.
- Record the model, installation date, and replacement information somewhere accessible.
- If an alarm fails a test, follow its troubleshooting and replacement instructions promptly; do not leave the home without suitable working coverage.
Do not use a vehicle exhaust, flame, or improvised CO source to test a detector.
When Should You Replace a CO Alarm?
Use the replacement date and service life specified for the exact model. Replace an expired, failed, or end-of-life unit rather than assuming new batteries will restore its sensor. If its age or replacement instructions are unclear, contact the manufacturer or qualified service provider promptly.
For example, Kidde’s replacement guidance describes model-dependent lifespans and exceptions. It should not be turned into a universal lifespan for every brand, power source, or monitored detector. Do not wait for a warning signal if the scheduled replacement date has already arrived.
CO Alarm Sounds vs. Trouble Signals
Learn the model’s CO alarm, low-battery, trouble, and end-of-life signals from its manual. A single chirp or a particular number of beeps is not a universal diagnosis. Voice messages and status lights may provide additional information.
If you cannot tell whether a signal means CO, get outside and call 911. If the CO alarm is sounding or you suspect exposure, follow the same emergency response. Do not stay inside to troubleshoot a possible CO emergency.
What Does Professional CO Monitoring Add?
A local alarm warns people who can hear it. A connected app may notify designated users. With compatible equipment and an active monitoring service, a supported CO signal can also reach a monitoring center.
ADT’s CO detector information describes monitored detection, local alarms, and supported mobile alerts. Exact equipment, compatible controls, enrollment, power, communication paths, and service terms affect which capabilities apply to a particular home.
SafeStreets sells, designs, and professionally installs ADT-monitored home security systems; ADT provides the 24/7 professional monitoring. Ask how CO events are handled, what contacts or emergency-response procedures apply, and what backup power and communication the quoted setup provides.
Monitoring is an additional response path, not a guarantee of signal delivery, a fixed response time, or emergency dispatch in every circumstance. During a CO alarm, get outside and call 911 rather than waiting for someone to contact you.
Local Requirements and Professional Installation
Requirements vary by location, property type, and work being performed. Ask your local building or fire official about required locations, power, interconnection, and responsibilities for the property. A generic guide or a product listing is not a determination that a particular home complies.
For federally assisted housing, consult the applicable program’s current requirements and HUD’s CO alarm and detector notice announcement. Owners and managers should confirm which requirements apply rather than assuming one rule covers every rental property.
A professional home security installation consultation can help you discuss compatible monitored equipment and its placement. Confirm the scope of work; appliance servicing and electrical work may require other qualified professionals.
Alarms Complement Safe Equipment Use
Have fuel-burning appliances and venting maintained by qualified professionals. Do not use an oven or gas range to heat the home, burn charcoal indoors, or leave a vehicle running in an attached garage, even with the door open.
Follow the CPSC’s generator safety guidance: operate portable generators outdoors, at least 20 feet from the home, with exhaust directed away. The CDC also advises keeping them more than 20 feet from windows, doors, and vents. Never use one inside a house or garage, even with doors or windows open.
See the U.S. Fire Administration’s CO safety information for additional prevention guidance.
Discuss Monitored CO Detection With SafeStreets
Homeowners can ask SafeStreets about compatible CO detection, placement, and ADT monitoring as part of a home security plan. Equipment shown is illustrative; confirm the exact models, features, installation eligibility, monitoring, and applicable terms in your quote. The property owner must hold the SafeStreets agreement.
SafeStreets is ADT’s only Authorized Provider and has 185,000+ reviews with a 4.9 average rating across Trustpilot and Google.
Get a free quote or call 855-891-7233 to discuss installation. This is a sales contact, not an emergency line; call 911 for a CO emergency.
Frequently Asked Questions
What should I do when a CO alarm goes off?
Move everyone outside to fresh air immediately and call 911 from outside. Do not search for the source or wait for a monitoring call. Stay outside until emergency responders permit reentry.
Is a CO alarm the same as a smoke alarm?
No. They detect different hazards. A combination smoke/CO unit is designed for both, but a smoke-only alarm does not provide CO detection. Check the product labeling and instructions.
How often should I replace my CO detector?
Follow the exact model’s replacement date and instructions, and replace it if it expires, fails, or gives an end-of-life warning. Do not rely on a generic lifespan or assume a new battery renews the sensor.
Can a CO alarm work without Wi-Fi?
Many alarms sound locally without Wi-Fi when they have the required power. Remote notifications and monitoring use the communication paths specified for the equipment. Check the entire setup’s power and outage behavior.
Should I put a CO alarm near the floor?
Not simply because of a belief that CO sinks. Follow the specific alarm’s approved mounting instructions and the home’s coverage requirements. Ceiling, wall, and plug-in installations are model-dependent.