Carbon Monoxide Alarm FAQs

CO detector
Carbon Monoxide is known as the "Invisible Killer" because it's a colorless, odorless, poisonous gas. Learn how to protect yourself and your loved ones from this deadly gas.
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What is carbon monoxide?

  • Carbon monoxide (CO) is an invisible, odorless and colorless gas.  It is created when fuels (such as gasoline, wood, charcoal, and petroleum products) burn incompletely.

Why is carbon monoxide harmful?

  • Carbon monoxide displaces oxygen in the blood and deprives the heart, brain, and other vital organs of oxygen.  Carbon monoxide poisoning can be fatal.  Symptoms include headache, fatigue, nausea, dizziness, bright red skin, mental confusion, loss of muscular coordination and loss of consciousness.

Where does carbon monoxide in the home come from?

Carbon monoxide sources include:

  • Heaters, fireplaces, furnaces, appliances, and cooking sources that use coal, wood, petroleum products, and other fuels.  Petroleum products include, but are not limited to, kerosene, natural gas, and propane.
  • Equipment powered by internal combustion engines, such as cars, portable generators, lawn mowers, and power washers.
  • Attached garages with doors, duct work, or ventilation shafts that are connected directly to a living space are also considered “carbon monoxide sources”.

What is a carbon monoxide alarm?

  • A device that detects carbon monoxide and produces a distinct audible alarm when CO is detected. It can operate either as a distinct unit, as two or more single station units wired to operate in conjunction with each other, or as part of an alarm system that contains CO detectors. 

In what buildings are carbon monoxide alarms required?

Oregon law requires CO alarms in certain residential occupancies as follows:

  • Rental dwellings with a CO source.  All rental dwelling units that either contain a CO source, or are connected by door, duct or ventilation shaft to a CO source. This applies to rental agreements entered into on or after July 1, 2010.
  • Sale or transfer of title of homes containing a CO source. This includes one and two family dwellings, manufactured dwellings, and multifamily housing units.  Alarms must be in place when the title is transferred.
  • New residential construction, regardless of whether or not there is a CO source, submitted for plan review as of April 1, 2011.  This includes any building alteration or repair for which a permit is required.

Are carbon monoxide alarms required in existing, owner-occupied single-family homes and duplexes?

  • No, they are not required in these homes by Oregon rules. However, it is a recommended best practice to have the alarms installed in any home that has a CO source.

What are landlord/tenant responsibilities?

  • In rental dwellings in which CO alarms are required (see above),  the landlord must:
    • Ensure that properly functioning CO alarms are installed.
    • Provide working batteries at time of move-in.
    • Provide the new tenant with alarm testing instructions.
  • Tenant must:
    • Test alarm at least every six months and replace batteries as needed.
    • Notify landlord in writing of any operating deficiencies.

Where in the home should carbon monoxide alarms be installed?

  • On each level of the home that has bedrooms or sleeping areas.
  • In each bedroom or within 15 feet outside of each bedroom door.
  • In multi-family buildings, an alarm is required in any enclosed common area that is connected by a door, ductwork, or ventilation shaft to a CO source.


  • Install CO alarms in a location specified in the manufacturer’s instructions. Depending on the model, this may be the wall, ceiling, or other location such as a plug-in receptacle.
  • Avoid locations that are in turbulent air such as near ceiling fans, heat vents, air conditioners, or open windows.
  • Avoid kitchens, garages, and furnace rooms, as installation in these areas could cause nuisance alarms.  Alarms should be placed more than five feet from fuel fired appliances.
  • Avoid locations that are dusty, dirty or greasy; these substances can contaminate or coat the alarm’s sensor, causing the unit to malfunction.

Do current rules require carbon monoxide alarms in all bedrooms?

  • No, the law requires an alarm within 15 feet of each bedroom door (for example, a single alarm in a hallway may be within 15 feet of two or three bedrooms). However, it is a recommended best practice to have them in each bedroom because ductwork from sources often goes directly to bedrooms, bypassing hallways outside of sleeping areas.

Do current rules require carbon monoxide alarms on all levels of the home?

  • No, the law requires an alarm on each level of the home that has bedrooms.  However, it is a recommended best practice to have alarms on each level of the home.
Common sources of Carbon Monoxide

What are acceptable power sources for CO alarms?

CO alarms can be:

  • Battery operated.
  • Hard-wired with a battery backup.
  • Plug-in with a battery back-up.

What are the maintenance requirements for carbon monoxide alarms?

  • Carbon monoxide alarms must be maintained and tested according to the manufacturer’s instructions. This usually includes:
    • Periodic (weekly) testing.
    • Vacuum to keep alarm free of dust and debris.
    • Replace batteries as needed.
  • Most CO alarms have a 5-year life span. 

What should people do when the carbon monoxide alarm sounds?

  • Silence the alarm.
  • Move everyone outside to fresh air and call for help from an outside location.
    • If anyone is experiencing symptoms of CO poisoning, call 9-1-1.
    • If no one has symptoms, ventilate building and contact a qualified service technician.
  • Have all home equipment powered by fuels such as gas, wood, or petroleum products inspected by a qualified technician.
  • Have fuel-burning heating equipment and chimneys inspected by a professional every year before cold weather sets in.

CO Alarm troubleshooting tips:

Occasionally a carbon monoxide alarm will sound when there are not elevated levels of CO in the home.  Possible explanations include the following.

  • Low battery.
  • Dust, debris or other substance in the alarm.
  • Poor placement of the alarm (e.g. in a garage or too close to a fuel fired appliance).
  • Alarm has reached the end of its life. Some newer alarms have an audible “end of life” signal.  When it is time for replacement, the alarm will sound a tone such as a chirp every 30 to 60 seconds.
  • Alarm malfunction.  Some alarms have self-diagnostic tests that will sound an audible alert when alarm malfunctions.  This sound could be an intermittent chirp or a continuous tone.
  • A transient CO situation. For example:
    • Reverse venting of fuel burning appliances caused by exterior conditions such as wind or temperature inversions which can trap exhaust gases near the ground.
    • Vent pipe connections vibrating loose from appliances such as clothes dryers, furnaces or water heaters.
    • Extended operation of fuel burning devices (range, oven, fireplace, etc.).
    • Car idling in an attached garage or near the home.

Where do I get more information?

Oregon State Police
Office of State Fire Marshal
4760 Portland Road NE
Salem, OR 97305

  • Oregon Administrative Rules (O.A.R. Chapter 837)
  • Oregon Revised Statutes (O.R.S. Chapter 90, Chapter 105, Chapter 476)
  • NFPA 720: Standard for the Installation of Carbon Monoxide (CO) Detection and Warning Equipment
  • The U.S. Consumer Product Safety Commission (CPSC Document #466)


Portland Fire & Rescue - Public Education Office