Smoke & Carbon Monoxide (CO) Alarms: 101

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Blog by Due North Property Inspection

Having properly placed smoke and CO alarms throughout your house is critical to protecting your family and home.  Many homeowners are not fully aware of the types of alarms, where they need to be placed, and other information critical to keeping their family safe from fire and CO. This article will help layout the basics of what you need to know to make sure your home and family are well protected. 

Types of Smoke Alarms

When it comes to smoke detection, there are three different types of alarm technologies to consider: ionization smoke alarms, photoelectric smoke alarms, and dual-sensor devices. These alarms detect the presence of smoke differently and can respond quicker to different types of fires (smoldering vs. flaming).

  • Ionization smoke alarms are generally more responsive to flaming fires. 
  • Photoelectric smoke alarms are generally more responsive to smoldering fires.
  • Dual-Sensor smoke alarms are devices that contain both types of smoke detection technologies. 

No one can predict the time, location, or type of fire that may start in a home. Therefore, agencies such as the USFA (U.S. Fire Administration) and NFPA (National Fire Protection Association) recommend that both ionization and photoelectric alarms be used in homes, to ensure you are alerted to all fire types. 

If you had to choose just one, the IAFF (International Association of Fire Fighters) and ASHI (American Society of Home Inspectors) suggest that there is good reason to encourage the use of photoelectric smoke sensing technology over ionization or dual-sensor. Their recommendations are due primarily to homeowners disabling the batteries in ionization or dual-senor alarms because of nuisance/false alarms. Photoelectric alarms are significantly less prone to nuisance/false alarms and therefore are less likely to be disabled by annoyed homeowners. 

Smoke Alarm Placement

“The location of a smoke alarm within a home may be more important than the type of smoke alarm present, depending on the fire.” – U.S. Fire Administration

For residential houses, NFPA 72 - National Fire Alarm and Signaling Code has set the standard for the placement of fire alarms within the home. At a minimum, smoke alarms are required to be installed inside every bedroom, in addition to outside each sleeping area and on every level of the home. It’s important to note that homes built to earlier standards often do not meet these minimum requirements. Existing and soon-to-be homeowners should recognize that smoke and fire detection needs have changed over time and will continue to evolve. Regardless of the code that your home was built to, it is in everyone’s best interest to take proactive measures to make sure that every home has an ample amount of properly placed smoke alarms. 

Minimum Smoke Alarm Requirements:

  • Install smoke alarms inside each bedroom, outside each sleeping area, and on every level of the home, including the basement.
  • On levels without bedrooms, install alarms in the living room / den / family room or near the stairway to the upper level, or both.
  • Smoke alarms installed in the basement should be installed on the ceiling at the bottom of the stairs leading to the next level.
  • Smoke alarms should be installed at least 10 feet from a cooking appliance to minimize false alarms from cooking.
  • Mount smoke alarms high on walls or ceilings (smoke rises). Wall-mounted alarms should be installed not more than 12 inches away from the ceiling (to the top of the alarm).
  • If you have ceilings that are pitched, install the alarm within 3 feet of the peak, but not within the apex of the peak (minimum four inches down from peak).
  • Don’t install smoke alarms near windows, doors, or ducts where drafts may interfere with operation.
  • Never paint your smoke alarms. This can prevent proper operation.
  • For best protection, interconnect your smoke alarms. (When one alarm sounds, they all sound)

             - Interconnection can be done using hard-wiring or wireless technology

              - Use alarms from the same manufacturer for interconnecting applications.
                (all alarms are not compatible)

Due North recommendation:

  • At a minimum, make sure you have operating smoke detectors in all appropriate locations (listed above) throughout your home.
  • When it’s time to replace (every 10 years) or install additional smoke alarms, make the choice to use photoelectric smoke alarms.

Carbon Monoxide (CO) Alarms

Carbon Monoxide alarms alert based on the CO concentration levels in the air over time. This concentration-time function is intended to mimic the uptake of CO in the body while also preventing false alarms due to relatively common sources of carbon monoxide, such as cigarette smoke. There are four primary types of CO sensors available. They vary in cost, accuracy and speed of response.

  • Opto-chemical type sensors are used in the most cost-effective carbon monoxide alarms. The sensor uses a pad that changes colors when CO is detected. Although these detectors may be more affordable, they are known to offer limited protection. They only detect whether or not carbon monoxide is present, and offer nothing related to the actual carbon monoxide levels, leaving the homeowner uncertain as to the degree of danger.
  • Biomimetic type sensors use a combination of color-changing liquids or gel-like elements to detect carbon monoxide. Alarms that use this sensor typically last up to three years.
  • Metal-Oxide Semiconductor type sensors are created by using wired circuits to monitor carbon monoxide. Most detectors that use this sensor last up to 10 years.
  • Electromechanical type sensors are considered best-in-class and offer the most protection for homes when detecting carbon monoxide. This sensor is the dominant technology used in the US and Europe. For CO detection, the electromechanical sensor has advantages over other technologies in that it is highly accurate, requires minimal power, and has a long lifetime. 

CO Alarm Placement

The statutes and codes related to CO alarm requirements vary from state to state. For the sake of this article I’m going to focus on the requirements for my home state of Minnesota. Minnesota statute states “every single family dwelling and every dwelling unit in a multi-family dwelling must have an approved and operational carbon monoxide alarm installed within ten feet of each room lawfully used for sleeping purposes.” Minnesota building code reiterates this and states “carbon monoxide alarms shall be installed outside and not more than 10 feet from each separate sleeping area or bedroom. Alarms shall be installed on each level containing sleeping areas or bedrooms.”

Minimum CO Alarm Requirements:

  • Install CO alarms outside of and not more than 10 feet from all sleeping areas

               - Best placement is in the hallway or common area outside sleeping areas.
                 Placement in a bathroom, laundry room, or any room with a door on the
                 same level, even if it meets the 10 feet requirement, doesn’t work. 

  • Install at least one CO alarm on every floor
  • Make sure CO alarms are at least 15 feet away from cooking or heating      appliances to prevent false alarms.
  • Don't cover or obstruct the unit.

Due North Recommendation:

  • Install combination Smoke/CO alarms outside of but not more than 10 feet from all separate sleeping areas, and on every level of the house. Combination alarms are an easy way to satisfy one of your smoke alarm location requirements as well as a carbon monoxide location.
  • When it’s time to replace or upgrade CO alarms, make the choice to install a CO alarm with an electromechanical type sensor.

We hope this article gives you a better understanding of the types of smoke and carbon monoxide (CO) alarms available, as well as the requirements for locations throughout your home. Remember, fire and carbon monoxide don’t care when your home was built, or to what code. Take proactive steps to make sure your home and loved ones are protected.

Other Notes of Importance 

  • Replace your smoke alarms minimally every 10 years (manufacture date should be on the back of the alarm).
  • Replace CO alarms every 7 to 10 years (depending on your model) to benefit from the latest technology upgrades.
  • Test alarms once a month by pushing the test button.
  • Choose alarms that have the label of a recognized testing laboratory (ex. UL).
  • Keep manufacturer’s installation and operating manual for reference.
  • Specific to CO alarms, “installed” means that an approved CO alarm is either hard-wired into the electrical wiring, directly plugged into an electrical outlet without a switch, or, if the alarm is battery powered, attached to the wall of the dwelling.

Sites and Agencies referenced for this article:



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