May 18th, 2018

Safety’s No Accident: A New Year’s Resolution Has Us Buzzing about Alarms and Detectors – Part 3: CO Detector Price versus Function

by Jonathan Wilson

This is the third installment in a three-part blog series. Read parts one and two.

When I began a project to upgrade the fire alarms in my home to comply with Maryland state law, I considered whether to purchase a combined fire alarm and carbon monoxide (CO) detector. But as I noted in an earlier blog, the marketplace does not yet have devices that provide the two types of sensors needed to detect “flaming” fires and “smoldering” fires was well as a sensor to detect carbon monoxide. So I investigated (and ended up purchasing/installing) a stand-alone CO detector. This is what I learned along the way.

Carbon Monoxide Basics

CO is a colorless, odorless gas produced by fuel-burning appliances and equipment. At higher levels, it can turn deadly, as a recent well-publicized tragedy of a family vacationing in Mexico sadly reminds us. The Consumer Product Safety Commission (CPSC) estimates that in 2014, 130 people died in the U.S. from unintentional non-fire CO poisoning associated with consumer products at home. A 2011 study found that among CO deaths reported in the media, about 24 people died annually from automobiles left running in garages. An additional 50,000 people ended up at emergency departments for accidental CO poisoning.

Installation of CO detectors in any home with a combustion appliance or an attached garage is generally encouraged and sometimes required by law. Some safety experts note that the high incidence of poisonings from portable generators, grills, and engine-powered tools indicates that all homes should have a CO detector. From 2003 to 2014, the CPSC estimates there were more deaths from portable generators (696) than from faulty heating systems (611). Although my home is all-electric and we never park our cars in our attached garage, I felt it still made sense to purchase a CO detector to protect our family from nonpermanent sources of CO.

For house fires, the risk assessment is clear: fires ‎– bad; no fires ‎– good. Assessing the risks of carbon monoxide exposure is more complicated. Exposure to a concentration of 400 parts per million (ppm) can result in death in three hours. Double that level, and loss of consciousness can occur in one hour and death in two to three hours. And then there are the nonfatal risks at the lower levels. Toxic effects in healthy adults have been observed at 50 ppm, and studies have found impacts on people with heart disease at levels around 10 ppm. U.S. Environmental Protection Agency (EPA) standards require that average outdoor air levels not exceed 9 ppm over an eight-hour period.

The EPA reports that average CO levels within homes that don’t have gas stoves are 0.5-5 ppm, while levels in a kitchen with a properly adjusted gas stoves are often 5-15 ppm. Levels may exceed 30 ppm if gas stoves are not properly adjusted. (This points out the value of using kitchen range hood ventilation if you have a gas stove.) I tested my own home (no gas appliances), and my levels were less than 1 ppm.

CO Detector Basics

Just as smoke alarm manufacturers try to create devices that always warn you about a fire but don’t go off when something (such as toast, incense, or a cigarette) burns in your home, CO alarm manufacturers have tried to strike the same balance. Underwriters Laboratories have created a consensus standard (UL 2034) that applies to most CO detectors sold in the U.S. A UL 2034 detector will alarm:

  • In 4-15 minutes if CO exceeds 400 parts per million (ppm)
  • In 10-50 minutes if CO exceeds 150 ppm.
  • In 60-240 minutes if CO exceeds 70 ppm.

Per UL 2034 standards, a CO detector cannot alarm at CO levels below 30 ppm and can only be designed to alarm if levels exceed 30 ppm for at least 30 days. Most commercial brands do not alarm below 70 ppm. When purchasing a detector, you find that most CO detectors work pretty much the same way.

My Quest

The challenge for me as a consumer was to figure out what extras were worthwhile. A base CO detector is about $25-30. The main extras offered include:

  • Digital readout
  • Power source/life
  • Interconnectivity

Digital Readout

If you’re worried about CO levels below 70 ppm in your home, buying a device with a digital readout could offer further information about your exposure. But be sure to understand how the readout works. First off, most commercial devices will not display levels until they sense 30 ppm or more of CO. You are going to have to search for a device that regularly reads out at less than that value. Some devices will report levels below 30 ppm if a peak level button is pushed; but since these levels are not routinely displayed, you won’t know when and under what conditions the peak level was reached.

Some manufacturers are selling CO monitors that read out/alarm at lower levels (e.g., 10 ppm) as a service to people with heart or respiratory issues. But the manufacturers are clear that these monitors are often not in compliance with state/local laws and ordinances that require UL 2034 devices. You may need to purchase a “regular” CO alarm to comply with the law and then purchase this extra monitor for your own protection. And be aware, the cost can be six or seven times a standard CO detector.

I admit I didn’t do my homework and ended up buying a UL 2034-compliant detector with a display. Because CO levels in my home are well below 30 ppm, it always reads “0.” And because it always reads “0,” I never check the display. I paid about $10 extra for this feature that is essentially useless to me.

Power Source/Life

Today’s CO sensors generally last 10 years. Buying a sealed 10-year battery means you don’t ever have worry about battery replacement or worry that someone in your home might raid the device for a battery. Alternatively, you would buy a device with two or three AA batteries that should be replaced annually. A device with a 10-year sealed battery costs $20-25 more. If you buy your batteries in bulk, you might save $10 going with the replaceable batteries, although it’s pretty much a wash if you tend to buy batteries in four-packs. For peace of mind, I bought a device with the 10-year sealed battery.

Before investing in a device with a 10-year battery, it’s important to check the warranty on the device. If the warranty is only good for five or seven years, that may indicate that the sensor life is only rated for five to seven years. Don’t invest in the 10-year battery if you’re going to have to replace the unit in five years.

Buying a plug-in electric CO detector (or a hardwired) detector is another option that could offer further peace of mind. Carbon monoxide is slightly lighter than air but tends to mix fairly well with it indoors. Unlike smoke alarms, which should always be placed on ceilings or high on walls, CO detectors can be placed almost anywhere, as long as they are fully exposed to the air in the room (and are located as directed by the manufacturer). This gives people the option to plug CO detectors into standard knee-level electrical outlets. However, at my home, electrical outlets are at a premium and are often hidden behind furniture. Given that plug-in models offer less flexibility in placement and tend to cost $10-15 more than a 10-year sealed battery model (hardwired models cost even more), I stuck with the battery model.


I will be honest that I did not do a lot of research on interconnected CO detectors for my home, because I needed only one device to meet my home’s requirements. But it does strike me that this seems like a feature that is more important for smoke alarms than CO detectors. A fire in my basement could cut off escape routes quickly, so if I’m sleeping on the second home, I’ll want my upstairs alarm to go off as soon as possible. The very smart people at the National Fire Protection Association (NFPA) advocate for interconnected CO devices, but I don’t see why I’d have the same urgency to know that a CO level in my basement hit 70 ppm. Following the UL 2034 standard, that basement device itself doesn’t have to alarm until one to four hours after the CO sensor first registered the 70 ppm. It seems like a feature that adds unnecessary complexity to my home safety system and has limited benefit.

In retrospect, I could have saved $10 by skipping the display feature, but all in all, I’m pleased with my purchase. My family is now protected should an unexpected CO source (e.g., a portable generator used too close to my home) create a hazard. Whether it costs $4 or $5 per year of device performance, it is a product that provides peace of mind that is well worth the investment.


Jonathan WilsonJonathan Wilson, MPP, joined NCHH in 1993 and currently serves as Deputy Director and Chief Financial Officer. Mr. Wilson has authored more than 25 peer-reviewed research manuscripts evaluating assessment tools and interventions for healthy housing hazards. He also served as the NCHH representative to the federal Advisory Committee on Childhood Lead Poisoning Prevention from 2004 to 2010. He came to NCHH with a background in nonprofit housing development and a Master of Public Policy degree.


May 18th, 2018 | Posted By | Posted in Blog, Injury Prevention | Tagged , , , , , , ,