Carbon monoxide (CO) is a deadly invisible gas that has no smell and has thus been dubbed the silent killer as exposure to it can lead to serious injury leading to death. CO is a byproduct of burning materials like wood or gas so if you have fuel-powered appliances in the home, you need to be aware of this.
Regular smoke detectors only detect smoke and don’t detect carbon monoxide. A carbon monoxide detector specifically alerts you to elevated CO levels. A combination smoke/CO detector will alert you to both a potential fire and high levels of carbon monoxide in one product.
Carbon monoxide is a serious concern for any homeowner that has a fuel-burning heater, water heater, fireplace, stove or other appliances in the home.
Below is a discussion to learn more about how to tell if your smoke detector also detects CO, where carbon monoxide comes from, CO detectors and where to install them, and how you can better protect yourself against the dangers of this silent deadly gas.
Given that high levels of CO in your home can kill, it’s important to protect yourself accordingly and understand the difference between a smoke and carbon monoxide detector and what you have in your home.
How do I know if my smoke detector detects carbon monoxide?
The only smoke detectors that detect carbon monoxide are models that are designed to specifically detect both smoke and CO. A regular smoke detector will only detect smoke and not carbon monoxide.
So if you buy a smoke detector new, check beforehand to ensure you know exactly what it detects.
But what if you have existing smoke detectors and can’t tell? Perhaps you moved into a new house with existing smoke detectors and wonder if they have carbon monoxide detection built in.
How can you tell?
A carbon monoxide detector typically has a digital display that reads CO levels and is clearly marked as being a carbon monoxide alarm or detector as shown below.
Where should carbon monoxide detectors be installed?
CO detectors are often installed on walls at least several feet off the floor but not necessarily on a ceiling. Smoke detectors are typically located in the ceiling of homes as smoke rises and during a fire, the detector will trigger when the smoke rises.
A quality CO detector will have a digital display that gives an instant reading of the carbon monoxide level in the area that it is monitoring. The desirable reading is 0 since that indicates no presence of CO in that area.
Follow the instructions from your CO manufacturer as they normally give specific measurements and suggestions as to where and how to install your CO detector. This ensures you effectively monitor carbon monoxide levels while also making it easy to read the display of the unit.
How does a CO detector alert you to high levels of carbon monoxide?
A carbon monoxide detector is a time-weighted alarm which measures the buildup of CO in an area in a home over time. How quickly your alarm responds depends on the level of CO buildup and the time it has been measured: The higher the level of carbon monoxide the faster the alarm will trigger.
Carbon monoxide is released in the air by anything that burns such as wood, propane or gas and that comes into contact with oxygen. It is thus a concern if you have fuel-burning heaters, water heaters, fireplaces, stoves or other appliances in the home as a leak or other malfunction will produce CO.
A carbon monoxide detector will emit a very loud beep or series of beeps when a certain level of CO is detected. While a smoke detector will beep consistently until the smoke has cleared or it has been reset, a CO detector often has a series of 4 beeps followed by a pause and then a repetition when the alarm is sounding due to CO being present.
It may also beep once repeatedly when the battery is low so it’s important to understand how your model works. Also remember to change the batteries regularly. Some people pick a milestone date – every January 1 for example – to ensure fresh batteries are always being used.
But unlike a smoke detector which should immediately alert you to smoke which could indicate a fire, CO detectors are a bit more sophisticated in terms of how they respond as mentioned above.
How quickly will a CO detector alert you to elevated levels of carbon monoxide?
Kidde Fire Safety produces many CO and smoke detection systems for the home and defines how quickly their CO detectors respond as shown in the table below.
The left side of the table shows various levels of CO that may be measured by a detector, measured in PPM. PPM stands for Parts Per Million and is a measurement of the buildup of CO in the area of the home being monitored.
The right side of the table shows the time in which the CO detector will trigger (start beeping) when the associated level of carbon monoxide is measured.
| Carbon Monoxide Level in PPM | Alarm Response Time |
| 40 | 10 hours |
| 50 | 8 hours |
| 70 | 1 – 4 hours |
| 150 | 10 – 50 minutes |
| 400 | 4 – 15 minutes |
As you can see, the CO detector will track lower levels of carbon monoxide in a home without triggering the alarm until a large enough period of time has elapsed that indicates both a problem within the home as well as a threat to the health of people in the home.
These figures shown above correlate to the “acceptable” levels of CO that humans can be exposed to before their health is put in jeopardy.
What level of carbon monoxide is acceptable and when does it become dangerous?
Humans are able to tolerate low levels of carbon monoxide but dangerous levels can cause serious injury resulting in death if high exposure is excessive.
The following levels of carbon monoxide are defined with the associated CO readings.
| Carbon Monoxide Level | CO Reading in Parts Per Million (ppm) |
| Low level | 50 ppm and less |
| Medium level | From 51 ppm – 100 ppm |
| High level | 101 ppm with no one experiencing symptoms of CO exposure |
| Dangerous level | 101 ppm with someone experiencing symptoms of CO exposure |
8 hours of exposure at a maximum CO level of 50 ppm is the highest allowed in work environments by some safety agencies although in your local area the threshold could be different.
Even in houses without many CO-producing appliances it’s not unusual to have low levels of carbon monoxide, according to the EPA. Levels of 0.5 to 5 ppm are often found in homes without gas stoves, for example.
Where should CO detectors be installed in my house?
A CO detector can only monitor a specific area which is why you need to install multiple detectors within your home. It’s normally suggested to place a CO detector near – but not directly next to – carbon monoxide-producing appliances in your home such as a gas furnace and stove or fireplace and then at least one detector on each floor of your home.
Placing one directly outside each bedroom area is also important to quickly alert you should CO be detected.
Follow the instructions of the CO detector model that you buy and also abide by any specific local laws or recommendations as they can differ depending on where you live.
The sooner you are alerted to an elevated level of CO anywhere in the home, the sooner you and everyone in the house can quickly exit the home and then call for help.
Do carbon monoxide detectors go bad and need to be replaced?
Like smoke detectors, CO detectors do expire and should be replaced according to the date shown on the model you buy. CO detectors have some delicate plastic and metal parts and over time they wear out.
CO detectors that you install in your home have sensors that can deteriorate especially if they come into contact with carbon monoxide and other chemicals in the air over time and lose their sensitivity and effectiveness.
Many CO detectors last upwards of 7 years and some newer models can last as long as 10 years. You might be better served replacing yours every 5 years especially if that is what is recommended.
Also, over time technology is improved upon and replacing your CO detector ensures you have the most recent available model in your home.
Given the cost of replacing CO detectors, it’s a fair tradeoff for something that can potentially save the life of you and those in your household.
NOTE: Some CO models beep 5 times per minute consistently which indicates that the end of the life has been reached and the CO detector needs to be replaced.
Do CO detectors detect natural gas or propane leaks?
CO detectors are designed to only detect carbon monoxide but not natural gas or propane and certainly not smoke or fire for that matter. It will not detect a gas leak as that is not what it was designed to do.
Carbon monoxide is produced when fuel like gas or wood is burned in the presence of oxygen (O) and the subsequent byproduct that is produced is CO which is highly dangerous when inhaled and when it is built up indoors with poor air circulation.
Natural gas supplies into homes are often treated with a chemical called mercaptan which gives the gas a foul-smelling odor similar to rotten eggs to alert residents of a gas leak.
But carbon monoxide has no smell and is invisible and thus requires a carbon monoxide detector to alert you to high levels within your home otherwise you would not know potentially resulting in a fatality.
Only a CO detector can detect and measure levels of carbon monoxide and alert you when it becomes dangerous.