Know Before Buying

what to know before you buy CO detectors

With over 25-year's experience in using, testing, and calibrating CO detectors, we’ve learned a few things about the differences in CO detectors...

To begin, what is carbon monoxide (CO) and how is it created?

Carbon monoxide is a colorless, odorless, poisonous gas. CO is the by-product of the incomplete combustion of fuel sources such as natural gas, propane, diesel, gasoline, wood, and many others. Basically, anything that does not run on electricity, batteries, or a renewable energy source is most likely being powered by a fuel which can produce toxic, dangerous levels of carbon monoxide.

What are some common appliances and equipment that generate CO?

Any fuel-burning motor or household appliance can be a potential source of fatal or hazardous CO levels, including:

  • Heaters and furnaces
  • Wood burning stoves
  • Stoves and ovens
  • Water heaters
  • Fireplaces
  • Clothing dryers
  • Car, trucks, motorcycles
  • Generators, lawnmowers, gas powered tools
  • Shop heaters, wood burning stoves, fireplaces

What is considered an unsafe level of CO for my home, business, RV - or even outside?

Depending on which organization you ask, the answer varies. Most health professionals agree prolonged exposure to CO, even for healthy people, poses an unnecessary risk that can be avoided. Furthermore, medical studies in the US have confirmed that prolonged exposure to CO - even at levels below 9 ppm - can pose serious health risks for pregnant woman, children, the elderly, or anyone with a serious medical condition.

Unfortunately, most CO detectors marketed to consumers are not required to alarm until CO levels reach 30 ppm for 30-days; far beyond what most health experts consider safe.

As a reference, the following organizations recommend and or enforce the following CO levels for both inside and outside buildings:

  • US EPA: no more than 9 ppm max over 8-hour period for outside levels
  • World Health Organization: no more than 9 ppm max over 8-hour period, or 6 ppm over 24-hour period
  • ASHRAE: no more than 9 ppm for indoor levels
  • NIOSH: no more than 35 ppm over 8-hour period
  • OSHA: no more than 50 ppm over 8-hour period
  • US Fire Departments: at 25 ppm or higher, firefighters are required to wear a self-contained breathing apparatus in most cases.

Should I purchase a UL 2034 rated CO detector or a low-level CO detector – which is the best option and why?

In the US most people instantly gravitate toward UL-approved products. Why? Because we grew up with the UL brand and believe their “rating” means the product is safe. And in most cases, that assumption is correct.

However, based on the recommendations above, many health experts believe UL 2034 rated CO detectors have an inherit flaw as they are not required to sound an alarm until CO concentrations reach 30 ppm for 30-days. Considering the thresholds published by the leading organizations above, CO detectors in this class would leave people at risk of long-term, low-level exposure to CO poisoning.

Here’s a brief summary of the requirements for UL 2034 CO detectors:

  • 0 – 29 ppm: Unit must remain silent and if it has a digital display the display must show a zero reading. *Note: The Defender CA6150 CO Alarm has a small “work around”. With one touch of a button, you can monitor current CO levels as low as 10 ppm.
  • 30 ppm – 69 ppm: When CO concentrations have been continuously sustained in this range for a minimum of 30 days an audible alarm may sound (but it is not required). Units with a digital display should display CO concentrations when measured 30 ppm or higher but it is not required.
  • 70 ppm – 149 ppm: Alarm must sound when CO levels have been continuously sustained in this range for 60 minutes, however depending on the CO detector it may take up to 240 minutes.
  • 150 ppm – 399 ppm: Alarm must sound when CO levels have been continuously sustained in this range for 10 minutes, however depending on the CO detector it may take up to 50 minutes.
  • 400 ppm and above – Alarm must sound when CO levels have been continuously sustained in this range for 4 minutes, however depending on the CO detector it may take up to 15 minutes.
Remember, these specifications only apply to CO detectors with the UL 2034 rating. Low-level CO alarms and detectors, personal CO monitors, and HVAC-intended CO detectors and analyzers will not have a UL 2034 rating – it would render them ineffective.

When might a UL 2034 rated CO detector be right for me?

To help reduce what UL defines as “false alarms”, CO detectors with the UL 2034 rating ensure that leading consumer CO detectors are not required to sound an alarm until CO concentration levels have been sustained for as long as four hours. From what we’ve learned over the years, the idea behind making the threshold so high (30 ppm sustained for as long as 30 days) was to reduce unnecessary calls to fire departments and EMS workers in areas which had “organically high” levels of CO concentrations, such as metropolitan cities with severe traffic. Often street-level apartments in high density, high traffic areas can have ambient CO levels as high as 10 ppm, sometimes even higher! So if you live in one of these areas and do not want to hear your CO alarm sound until CO concentrations in your home reach 30 ppm or higher for a month, a UL 2034 rated CO detector may be right for you.

Unfortunately, the UL 2034 standard remains in stark contrast to leading health experts who agree monitoring against low levels of carbon monoxide is the best approach. CO detectors that fail to alarm until CO concentrations are sustained at 30 ppm or higher leave a number of susceptible people at risk, especially children, pregnant woman, the elderly, and anyone with an underlying respiratory or severe health condition.

What primary types of CO detectors are available, and what are the key differences?

For the most part, CO detectors available to consumers can be separated into three primary categories:

  • Residential and light commercial CO detectors which can be mounted to a wall or placed on a table.
  • Personal CO detectors, or wearables, designed to be used indoors, outdoors, inside vehicles, or while traveling.
  • Industrial-grade CO detectors designed for HVAC technicians and industry professionals.

What is the typical response time of a CO detector?

Response times vary widely depending on the type of CO detector. Typically the fastest responding CO detectors are those used for personal monitoring (wearables) or those with an internal pump designed for HVAC and industrial testing. High quality, fixed units will also respond relatively quickly (less than a minute) to both low and high levels of CO exposure. Before choosing a CO detector, be sure to review the manufacturers specifications to ensure the detector you choose meets the health and safety standards you are following. If you have any questions, feel free to email us at

Can CO detectors be calibrated?

Some can, but most CO detectors for homes and offices cannot. Personal CO detectors, such as Sensorcon and BW, and CO detectors and analyzers designed for HVAC and industrial applications, can often can be calibrated and serviced as necessary.

How long do CO detectors last and or what is the typical warranty?

Depending on the manufacturer and type of CO detector, warranty periods vary from one year to 10-years. Why such a wide span? Mostly it has to do with the type of intended use and quality of CO sensor used. As you can imagine, a personal CO detector designed for use in harsh conditions will not have the same life expectancy (and therefore warranty) as a wall-mounted CO detector designed for home or business use. Additionally, we have personally found that CO detectors manufactured in China are not as reliable as their North American counterparts.

Personal CO detectors (also known as wearables) typically have a 1 -3 year or warranty period. Fixed or wall-mount CO detectors designed for residential and or commercial use typically have a 5 to 10-year warranty.

Best Selling Models:

  • Home: Defender Low Level CO (Carbon Monoxide) Monitor - LL6170
  • Office: Defender CD8180 Battery Powered Commercial CO Detector (with digital display)
  • Travel: Sensorcon Inspector Industrial Pro (CO) Carbon Monoxide Detector Meter
  • Personal: Sensorcon Inspector (Standard) Carbon Monoxide Detector & CO Meter