What Does a Carbon Monoxide Detector Do and How Does it Work?

It might seem like a time-saver to run your car in the garage before a long commute, especially on a cold winter’s morning. But the emissions from your vehicle can fill your garage with carbon monoxide (CO)—a dangerous, silent threat—even if the garage door is open.

Carbon monoxide is a colourless, odourless, and poisonous gas that claims over 250 lives a year in Australia.

It’s a byproduct of burning carbon fuel like the natural gas in your stove and the petrol in your car. Even small doses of carbon monoxide can cause permanent damage or death.

What does a CO detector do?

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About carbon monoxide

What is carbon monoxide?

Carbon monoxide gas is a simple molecule: one part carbon and one part oxygen. Carbon monoxide comes when carbon fuel—like wood, gasoline, coal, propane, natural gas, and heating oil—fails to burn completely (incomplete combustion).

These energy sources aren’t dangerous when you burn them in an open area with plenty of ventilation. But carbon monoxide is hazardous in confined spaces—like basements, kitchens, garages, or campers.

Carbon monoxide is hard to detect without a sensor, which is one of the reasons it’s so dangerous.

Sources of carbon monoxide gas


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Why is carbon monoxide dangerous?


These are the early symptoms of carbon monoxide poisoning:

  • Headache
  • Nausea
  • Vomiting
  • Dizziness
  • Shortness of breath
  • Fatigue

Perhaps most troubling is the similarity to cold or flu-like symptoms that are easy to ignore—shortness of breath, nausea, and mild headaches. Disorientation and unconsciousness can occur when levels of carbon monoxide reach 150 parts per million (ppm). Eventually, the symptoms turn lethal without treatment.

How can I prevent carbon monoxide poisoning?

Carbon monoxide poisoning is a serious risk, but fortunately, it’s preventable. Here are five tips for avoiding exposure, including installing sensors throughout your home.

  • Never heat your home with a gas range. Gas stoves produce carbon monoxide and can fill your home with the dangerous gas.
  • Don’t run your car in the garage. If you want to warm up your vehicle in the winter, pull out of the garage first. Carbon monoxide is a common byproduct of vehicle exhaust and builds up quickly in a closed (or even open) garage.
  • Always have proper ventilation. It’s extremely dangerous to run gas-powered tools (like generators, space heaters, and pressure washers) in an enclosed area like a basement or garage without adequate ventilation.
  • Practice cooking safety while camping. You should enjoy the wilderness safely. Don’t use a charcoal grill, hibachi, or camping stove inside your home, tent, or camper. Besides, open flames and fabric tents don’t tend to get along.

Detecting carbon monoxide

How do you detect carbon monoxide?

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Carbon monoxide detectors are the fastest way to prevent CO poisoning. You can install a carbon monoxide alarm (or multiple detectors) in your home. They work much like your fire or smoke alarm by sounding a siren when they detect carbon monoxide.

You can find simple models that set off a siren, or smart detectors like the Google Nest Protect that connect to your smartphone or home security system.

How do carbon monoxide detectors work?

Carbon monoxide detectors sound an alarm when they sense a certain amount of carbon monoxide over time. Different sensors set off different types of alerts:

  • Biomimetic sensor: a gel changes colour when it absorbs carbon monoxide, and this colour change triggers the alarm.

Once the carbon monoxide detector alarm sounds, it must be in a carbon monoxide-free environment to silence the siren.

When will my carbon monoxide detector go off?

The CO alarm sounds if your sensor detects a buildup of carbon monoxide in your home—usually before you start sensing symptoms. With a low CO level (50 ppm), it may take up to eight hours for the alarm to go off. Higher levels (over 150 ppm) can trigger an alarm within minutes.

Act quickly when an alarm sounds because low doses over long periods can be just as dangerous as sudden carbon monoxide exposure in ultra-high doses.

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How much CO does it take to make me feel sick?

Most people begin to feel the effects of carbon monoxide exposure at 70 ppm. This is why it’s important to have CO detectors since lower levels don’t bring obvious symptoms.

What do I do if my carbon monoxide detector goes off?

  1. First, don’t panic. Gather everyone in your house and move outside for fresh air.
    • On the way outside, open as many doors and windows as possible to help air out your home. To reduce exposure, don’t go out of your way to open every door and window, just the ones along the way.
    • Know the difference between an actual alarm and the detector's "end of life" alarm, which has a different sound.
  2. Survey everyone’s health and check for any flu-like symptoms that could suggest poisoning.
  3. If you notice any symptoms, call 000 immediately.
  4. If possible, do not reenter your home until the alarm stops sounding or emergency responders deem your home safe.
  5. Contact a professional to evaluate every fossil fuel-burning appliance (particularly heaters and stoves) and any other possible source of carbon monoxide to prevent a future incident.

Regular maintenance and inspections can help prevent safety hazards in your home.

Choosing a carbon monoxide detector

What kind of carbon monoxide detector should I get?

Overall, carbon monoxide detectors sense CO fast and alert you as soon as they do. But there’s a surprising amount of variety in today’s carbon monoxide sensors.

Some simple models plug into outlets or use a battery and alert you with a loud siren, like the one on your smoke detector. These models are cheap and suitable for multi-room buildings that need several units spread throughout.

Many models include sensors for both smoke and carbon monoxide. These are an easy option that you can swap out your existing smoke detectors for. They also reduce the number of sensors on your walls or ceilings.

You can also find smart models that connect with your smart home system or alert you of danger through a mobile app. These models are expensive but can be a wise investment if you want extra safety for kids and pets at home.

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Sensor maintenance

No matter what type of carbon monoxide detection you have, you should conduct regular maintenance:

  • Test it frequently using the button on the front (once a month).
  • Replace the batteries as often as the instructions recommend.
  • If you have a wired sensor with a battery backup, make sure both power sources are working.
  • Replace the sensor every few years according to manufacturer guidelines. (These sensors don’t last forever.) Many models intentionally sound an alarm when they expire; read the manual so you know what to expect.

Where should I place a carbon monoxide detector?

Ensure everyone in the house can hear when an alarm goes off by placing a CO sensor in or near each of three critical locations in your home:

  • At least one on each level—including the garage
  • Near each bedroom or sleeping space
  • By doors that lead to attached garages

Follow the manufacturer’s instructions for additional guidance beyond these three locations.

How many carbon monoxide detectors do I need?

Carbon monoxide detectors aren't required by law in Australia, so there's no hard and fast rule for how many you need. Really, it comes down to personal preference. You may like to stick with one on each level of your home, or perhaps have one in every room.


John Carlsen
Written by
John Carlsen

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