Identifying CO detectors vs. Smoke detectors

I’am a home inspector and I always have a hard time identifying CO detectors vs. smoke detectors. Does anyone have a little trick or advice to give me on Identifying the CO detectors?

Some CO detectors will be plugged into a standard wall receptacle and are easy to identify. Most of the ceiling mounted CO detectors I have seen are labeled as CO. Now then, some of the combination CO/smoke detectors don’t have any labeling and you would have the take them apart.

Pushing the test often reveals what type of detector it is.

How’s that? The smoke detector beeps. What do you hear to differentiate the ceiling mounted Smoke vs Smoke/CO?

I have seen some that are labeled Smoke/CO, but also wondering.

Many modern detectors have voice alert that says “fire” and/or “warning carbon monoxide” or similar.


The label on the unit will indicate what it is. Most use raised lettering - aim your flashlight at it from the side to cast some shadow from the lettering and take a photo. You can zoom the photo and tell.

A cheat with First Altert/BRK is that they use black lettering on their combination CO/Smoke alarms, whereas the smoke only doesn’t have black lettering.
Smoke only: image
Combo: image

Sounding voice alarms gives you a definitive answer.


I generally get my ladder and take them down to look at the manufacture date. Ten year old alarms should be replaced. Combination alarms will always have two separate ports, one for smoke - one for CO, although there are some alarms where this is hard to see. Since this is a safety item there are no shortcuts!

You take the smoke detector down. You must be the most thorough home Inspector out there

Gary Witt

Louisville Home Inspections, LLC

(502) 415-6709 or (502) 7100-2100


Hardly, Maryland has laws regarding smoke detectors in a Real Estate transaction. It’s called CYA! If you don’t practice those three letters you won’t be around long!

Bring binoculars on your inspections?

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Smoke detectors are part of an alarm system. You are looking at smoke alarms. Different animals.