How can I tell the difference between a smoke detector and carbon monoxide (CO) detector?

Tuesday, July 30, 2019

Here’s a few pointers to help you determine whether you have a smoke alarm or carbon monoxide ((CO) alarm, and maybe without having to unmount it: 

1) Hard-wired smoke alarms are usually found in hallways and/or bedrooms, on or near the ceiling, and they often have no visible designation on the face or it is faintly embossed in the plastic. Battery-powered smoke detectors can found installed anywhere around the home by a homeowner, including garage, kitchen, and even the attic.

2) CO alarms are currently required to be in the hallway or access area to each bedroom although, again, you might find one anywhere around the house. They are more likely to be clearly marked on the face as carbon monoxide. Where you find two detectors mounted side-by-side, one is likely to be a CO detector. Then again, sometimes one of them is a long-dead smoke detector left in place. 

3) Any detector device plugged into a low wall receptacle will be carbon monoxide. They are usually a rectangular shape.

4) Most builders comply with the requirement for both a CO and smoke detector in the hallway or access room to bedrooms of new new homes, which has been enfored since 2008 in Florida, by installing a combination CO and smoke detector at the double-requirement locations. They are usually clearly marked, but can also be verified by pushing the test button and hearing both a “WARNING CARBON MONOXIDE!” and “WARNING FIRE!” voice recording on many models.

5) If still undetermined, remove the smoke detector and examine the back. On most, but not all, smoke detectors you will also an find the date of manufacture stamped in small letters. Smoke detectors older than 10-years have exceeded the manufacturer’s rated lifespan and should be replaced.

6) Never assume that the all the smoke detectors are hard-wired with a battery backup because it is a newer house. The homeowner may have replaced some or all of them with battery-powered detectors mounted over the hard-wire box. If this is a concern, remove one or two of them at random and examine the back.

• • • • • • • • • • • • • • • • • • • • • • • •

Here’s links to a collection of our blog posts about SAFETY:

 What is the best place to install carbon monoxide alarms (CO detectors) in a house? 

 Why is it important to use "cabinet screws" to mount the upper cabinets in the kitchen?

 Is the door between an attached garage and the house required to have a closer (self-closing device)?

 Can the smoke sensors in a home security/fire alarm system replace the smoke alarms required by the building code?

 Should I get a lightning rod system to protect my house? 

 What are the "Aging In Place" features to look for when buying a retirement home?

 What is aging in place? 

 How do I safely remove a dead rodent (rat, mouse or squirrel) from the attic?

 Does pushing the test button on a smoke alarm test the smoke sensor device inside? 

 What is the minimum height of a ceiling fan above the floor?

 Should a smoke alarm be installed in the kitchen? 

 Why is a double cylinder deadbolt lock on an exterior door a safety hazard?

 Why are rubber washing machine hoses a safety risk?

 What can I do to avoid kitchen accidents and injuries?

 Where are smoke alarms required to be located? 

 Are carbon monoxide alarms required to be installed in homes in Florida?

 Are old vinyl tile floors dangerous?  

 How can I use safety checks to limit my tenant liability for a rental house?

 Do you inspect for trip hazards around the home? 

 When should I replace my smoke alarms?

• Why is an anti-tip device now required behind the range? 

• What are the hazards to avoid when going into an attic? 

What are the warning signs of a dangerous deck?

Which trees are most likely to fall over on your house in a hurricane?

    Visit our SAFETY page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.

How To Look At A House

McGarry and Madsen's home inspection blog for buyers of  

site-built, mobile/manfuactured and modular homes






Air Conditioner & Furnace Age/Size




Aging in Place


Click Below  

for Links

to Collections

of Blog Posts

by Subject


Doors and Windows


Energy Efficiency

Fireplaces and Chimneys

Heating and Air Conditioning

Home Inspection

Hurricane Resistance

Electrical Receptacle Outlets

Electrical Panels

Garages and Carports

Common Problems

Exterior Walls & Structures



Life Expectancy

Mobile/Manufactured Homes

Older and

Historic Houses

Mold, Lead & Other Contaminants

Modular Homes

Metal Roofs



Pool and Spa

Roof and Attic




"Should I Buy A..."


Termites, Wood Rot

& Pests

Structure and Rooms


Water Heaters

Water Heater Age

Septic Tank Systems

Plumbing Pipes


When It First

Became Code

Park Model Homes

Shingle Roofs


Wind Mitigation Form

"Does A Home


"What Is The Difference Between..."


Concrete and

Concrete Block


Rain Gutters


Crawl Spaces

Building Permits

Clay Soil




HUD-Code for

Mobile Homes

Flat (Low Slope) Roofs

Sprinkler Systems

4-Point Inspections

Frequently Asked Questions (FAQ)

Building Codes

Inspector Licensing

& Standards

Washers and Dryers



Electrical Wiring

Plumbing Drains

and Traps

Smoke & CO Alarms

Top 5 results given instantly.

Click on magnifying glass

for all search results.



Electrical Switches


Water Intrusion

Electrical - Old

and Obsolete

Foundation Certifications

Tiny Houses

About Us