You can test for carbon monoxide in two ways: with a CO detector in your home that monitors the air, and with a blood test at a hospital that measures how much CO has entered your bloodstream. Most people searching this question want to know whether their home is safe, so the most immediate step is making sure you have a working CO alarm and know how to verify it’s actually detecting gas, not just making noise.
What CO Detectors Actually Test
Every CO detector has a test button, and pressing it confirms the buzzer, LED lights, and electronics are working. But here’s what most people don’t realize: the test button does not verify that the sensor is detecting carbon monoxide gas. It only checks that the alarm can sound. Your detector could have a dead sensor and still pass a button test with flying colors.
To confirm your detector can actually sense CO, you need to expose it to real carbon monoxide gas. CO test cans (small aerosol canisters containing a controlled amount of CO) are available online for about $15 to $30. You spray the gas directly onto the detector’s sensor, and if the unit is functioning properly, it should trigger an alarm within a few minutes. The recommendation is to press the test button weekly or monthly and expose the detector to actual CO gas once per year.
Where To Place Detectors in Your Home
A single detector isn’t enough for most homes. The EPA recommends placing a separate detector on each floor, and if you’re only getting one, it should go near the sleeping areas where the alarm can wake you up. CO mixes fairly evenly with air (it’s nearly the same density), so wall-mounted or ceiling-mounted units both work, but you should follow the manufacturer’s specific installation instructions for your model since sensor placement affects performance.
Common CO sources in a home include gas furnaces, water heaters, stoves, fireplaces, attached garages, and portable generators. Placing detectors near these areas (but not so close that normal brief spikes trigger false alarms) gives you the earliest warning.
When To Replace Your CO Alarm
CO alarms need to be replaced every seven years. The electrochemical sensors inside degrade over time regardless of whether they’ve ever detected gas. When a unit reaches the end of its life, it will typically beep every 30 seconds or display “ERR” or “END” on the screen. This is not a low-battery warning. It means the entire unit needs to go. Check the manufacture date printed on the back of yours. If you can’t find one, or if it’s older than seven years, replace it now.
Professional CO Testing
If you suspect a specific appliance is leaking CO, an HVAC technician can run a combustion analysis. They use specialized analyzers that measure CO, oxygen, carbon dioxide, and draft pressure simultaneously in the exhaust gases of your furnace, boiler, or water heater. This pinpoints exactly which appliance is malfunctioning and whether it’s producing dangerous levels of CO during normal operation. A standard home detector tells you CO is present in the room but can’t tell you where it’s coming from.
For context on dangerous levels: the workplace safety limit set by OSHA is 50 parts per million averaged over an eight-hour workday. NIOSH, which tends to be more conservative, sets the limit at 35 ppm with a ceiling of 200 ppm that should never be exceeded. Most home CO detectors are calibrated to alarm at around 70 ppm after one to four hours of sustained exposure, which means low-level leaks can persist for a while before triggering an alert. A combustion analyzer catches those.
Testing Your Blood for CO Exposure
If you’re worried about actual exposure, the definitive test is a blood draw that measures carboxyhemoglobin, the percentage of your red blood cells that have bound to carbon monoxide instead of oxygen. Normal levels in nonsmokers are below 3%. Smokers can have levels up to 12% without acute poisoning symptoms, because they inhale CO with every cigarette.
Standard pulse oximeters, the clip-on finger devices used in most clinics, cannot detect carbon monoxide poisoning. They use only two wavelengths of light and can’t distinguish between oxygen-carrying hemoglobin and CO-carrying hemoglobin. This means your oxygen reading can look perfectly normal while you’re actually poisoned. Newer multiwave pulse oximeters use eight wavelengths and can estimate CO levels noninvasively, but these are specialized devices mostly found in emergency departments, not in a typical doctor’s office. A venous or arterial blood gas test remains the standard.
Timing matters for blood testing. When you breathe normal room air, CO clears from your blood with a half-life of about four to five hours, meaning your levels drop by half every four to five hours. With high-flow oxygen therapy, that drops dramatically. Under hyperbaric oxygen at high pressure, the half-life falls to roughly 23 to 53 minutes depending on the individual. So if you suspect CO exposure but wait hours before getting tested, your levels may have already dropped enough to look normal even if the initial exposure was significant.
Signs Your Home May Have a CO Problem
Beyond detector alarms, certain physical clues suggest a CO leak. Yellow or orange burner flames on a gas stove or furnace (they should be blue) indicate incomplete combustion. Soot or scorch marks around appliances, a stale or stuffy smell in a room with gas appliances, or excessive condensation on windows near those appliances are all red flags. Persistent headaches, dizziness, or nausea that improve when you leave the house and return when you come back are the classic symptom pattern of low-level CO exposure, sometimes misdiagnosed for weeks as the flu.
If your CO alarm does go off, leave the house immediately and call 911 from outside. Don’t try to find the source yourself. Fire departments carry handheld CO meters that can map concentrations throughout your home room by room and identify the leak quickly.