Carbon monoxide (CO) is a potentially deadly, odorless and colorless gas that is estimated to kill approximately 500 people a year and sicken many others. Often called the "silent killer," CO is a by-product of incomplete combustion and comes from malfunctioning appliances, such as gas or oil furnaces, wood burning stoves, and gas clothes dryers. When these appliances are not adequately ventilated, or if they malfunction, carbon monoxide can build up in the home to lethal levels. The list of potential sources of carbon monoxide also includes a wealth of items that shouldn't be used indoors under any circumstances, including portable generators and charcoal grills. Unfortunately, people don't always follow safety instructions and may use these items improperly.
According to MedlinePlus, a service of the National Institutes of Health, CO is the leading cause of poisoning in the United States. As noted by the Centers for Disease Control and Prevention (CDC), everyone is at risk from CO poisoning, though infants, the elderly and those with certain conditions, such as heart disease, are most at risk. If you are exposed to CO gas, you may notice symptoms such as "headache, dizziness, weakness, upset stomach, vomiting, chest pain, and confusion," the CDC notes. If you are asleep, especially if you're intoxicated, you're chances of dying from CO exposure are greatly increased.
The good news is that CO poisoning is highly preventable and the CDC's site has a long list of mostly common-sense steps to take. Those include servicing gas, oil or coal-burning appliances regularly, and not using items such as charcoal grills and camp stoves that are intended for outdoor use indoors. At the top of the list, however, is this advice:
"Install a battery-operated or battery back-up CO detector in your home and check or replace the battery when you change the time on your clocks each spring and fall."
All carbon monoxide detectors have a finite lifespan with sensors that wear out within five to seven years. However, the newest detectors come equipped with an end-of-life timer. When the time is up, the devices essentially self-destruct -- beeping at a regular interval until replaced. Don't just trust the timer, though. The National Fire Protection Association (NFPA) recommends that you "Test CO alarms at least once a month; replace them according to the manufacturer's instructions."
If a CO detector starts to chirp, don't ignore it, and don't remove the batteries to avoid the nuisance. Replace low batteries, or the device itself if needed, without delay. If the CO alarm sounds, respond immediately. The NFPA says to do the following: "Move to a fresh air location outdoors or by an open window or door. Make sure everyone inside the home is accounted for. Call for help from a fresh air location and stay there until emergency personnel [arrive].
The bottom line is that every home should have a CO detector, even if you don't have any gas, oil or wood-fired heating systems or appliances. A car accidentally left running in an attached garage, a neighbor with a malfunctioning appliance in an attached dwelling, or the accidental misuse of a standalone heating device during a power outage can all expose you and your family to CO gas.
When shopping for a CO detector, you will find that there are several different options to choose from:
Stand-alone carbon monoxide detectors work independently. These can be battery operated or plug into an AC socket (with a battery backup in the event of a power failure). They are the easiest type to install, but won't trigger other alarms in the home if they detect CO.
Interconnected carbon monoxide detectors form a network of alarms within your home. The connection can be hard wired or wireless, and the alarms can either plug into an AC outlet (with battery backup) or be completely battery operated. These can be made part of a network that also includes smoke detectors (which are reviewed in their own report). The advantage of an interconnected network is that when any one alarm sounds, they all sound, giving you an early warning of danger in a remote room, or one that's otherwise currently unoccupied. The disadvantage is that they can be the hardest to install. That's especially true of those that rely on a wired connection, as a circuit has to be run to all the alarms in the system -- a task that's much easier to do during construction or a major renovation than as an add-on to an existing structure. However, wireless interconnected CO detectors can be installed by virtually anyone and don't require any rewiring. Each detector can relay signals from one to another, setting up a mesh network that can cover your entire home.
Among stand-alone CO alarms, we saw the best feedback for the First Alert CO615 (Est. $30). It draws a Best Buy rating in one expert test, and over 1,000 mostly positive reviews, primarily from users posting at Amazon.com. The CO615 is AC powered, but no messy wiring job is required; instead, just plug it into a convenient outlet. While you can simply plug this CO alarm into a low-mounted AC outlet, the AC adapter is removable and is equipped with six-foot extension cord for placement "flexibility." This allows those looking for the best protection to place the detector higher on the wall (at least five feet above the floor) per the recommendations of most experts. Two AA batteries provide backup for continuous monitoring, even when AC power is out.
The CO615 isn't the most feature packed CO2 detector, but there are a few nice touches. The LCD display won't display continuous CO levels, but can show the peak CO levels over the last 24 hours at the touch of a button. The warning chirp if the back-up batteries become low can be silenced for eight hours. Some sites continue to list the existence of a feature that lets you silence the battery back-up warning with any standard IR remote control, but that feature proved to be problematic and has since been dropped.
Expert testing looks good for the CO615, though it's judged to be a touch better at detecting higher levels of CO than lower levels in the most reputable professional test we spotted. User reviews are also highly positive. We noted some gripes about build quality, particularly a battery door that's sometimes called flimsy, and a few found the CO detector challenging to use, or claimed that it arrived defective. However, those are well offset by a majority that seem mostly to completely pleased with the CO alarm. It rates a 4.4-star rating at Amazon.com.
If you prefer Kidde products, the Kidde KN-COPP-3 Nighthawk (Est. $30) is similar, and similarly well liked. In expert testing, the CO615 is judged to be a step better at detecting low levels of CO, and is said to have a higher-quality/more-effective display, but the Kidde is still a good performer on those counts as well. Users at Amazon.com rate the Kiddie a few tenths of a point higher, at 4.6 stars based on more than 1,300 reviews.
Like the First Alert, the KN-COPP-3 is designed to be plugged into an existing outlet, but, again, is equipped with a removable adapter for mounting higher on a wall or on a tabletop. Most users are extremely pleased, but we did see some comments claiming that the unit burns through back up batteries even when plugged in.
For those looking for a competent, easy-to-install carbon monoxide detector at the lowest possible price, things don't get much more basic than the First Alert CO400 (Est. $14). This CO alarm is battery powered, which gives you all the installation flexibility you might need -- though again it might be wise to heed expert advice to install it high above the floor. There's little in the way of features -- no readouts or voice warnings here -- just a button to silence nuisance alarms. User reviews are generally positive, but the battery compartment draws some ire. Two versions of the CO400 are offered -- one with two AA batteries that mount from the front, and a model with a 9-volt battery (newer and now more common) that mounts from the rear. It's the latter that seems to present a nearly insurmountable challenge to some. That might be why First Alert has posted a video on this CO detector's product page that shows how it's done.
While users tend to prefer the simplicity of stand-alone alarms, experts often prefer interconnected ones that can alert homeowners to issues in areas that are currently unoccupied. Among interconnected choices, we see good expert feedback for the First Alert CO511B (Est. $50). It's feature packed and easy to set up and use.
While many interconnected CO alarms require a messy and expensive hard-wired installation, the CO511B uses a radio signal is used to communicate between alarms. It's compatible with other First Alert wireless alarms, including the First Alert SA501CN-3ST (Est. $55) photoelectric smoke detector and the First Alert SCO501CN-3STU (Est. $50) combination CO and smoke detector; both are profiled in our report on smoke detectors.
The feature list on the CO511B goes well beyond its radio link, but that's a good place to start. The system establishes a mesh network, independent of other networks, such as Wi-Fi within your home. Each alarm acts both as a receiver and a transmitter, allowing the network to extend further. Security codes and frequency hopping technology establish stable and secure communications between alarms.
Other features include a voice alert that includes location information so that you won't be left guessing which alarm has sounded; up to 11 locations, such as a basement, can be programmed. Latching technology provides a visual indication of which alarm sounded after the alert has shut off. It also gives you a visual indication of which unit has a low-battery condition. The alarm tone sweeps through low frequencies to aid those with age-related or other hearing loss.
The First Alert CO511B does exceptionally well in expert testing. It draws a Recommended label in one independent review, with top ratings across the board for detecting high and low CO levels and for the quality of its voice alerts. User reviews, while not plentiful, are generally positive. Most say that installation is easy and that communication with other interconnectable First Alert alarms -- smoke, CO or combination, and either battery operated or hard wired -- work as advertised.
While the First Alert CO511B is a great choice for homeowners looking to add CO protection with a minimum of muss and fuss, if you are adding carbon monoxide alarms as part of new construction or a major remodeling job, you, or your contractor, might prefer a hardwired unit. The First Alert CO511B is completely battery powered and, while battery life should be reasonable, the batteries will need to be replaced periodically. A hard-wired CO alarm should have a battery as well (though not all do) to provide constant monitoring even during power outages; however, it's only a back-up, the main power will draw from your home's AC wiring.
Among hardwired interconnected CO detectors, we saw good feedback for the Kidde KN-COP-IC (Est. $45). It's not been professionally tested, but we found well over 125 user reviews spread over sites such as Amazon.com and HomeDepot.com, and the majority are very pleased.
Like the First Alert CO511B, the Kidde KN-COP-IC can be used in a network of compatible Kidde alarms, including smoke and combination CO and smoke detectors, interconnected via a simple wired network. Installation is reported as easy as long as walls are down; otherwise you might want to enlist the aid of an electrician to run the connections between units.
Installation considerations aside, The KN-COP-IC looks to be a fine unit. It lacks some of the features found in the CO511B, such as a voice alert, but adds others that the First Alert alarm lacks. Chief among those is a readout that displays CO levels, updated every 15 seconds. It also has a peak memory that can recall the highest CO level measured since the alarm was last reset.
While there are a number of sites that report on CO detectors, the only one we spotted that does current, credible testing is ConsumerReports.org. Editors there rate each detector on its ability to respond to both high and low levels of CO, and the quality and accuracy of the display or, if a feature of the tested alarm, voice message. Beyond that, we looked to the feedback from owners posting at sites such as Amazon.com, HomeDepot.com, Lowes.com and elsewhere. That feedback is extremely helpful in assessing things such as ease of installation and reliability -- including freedom from excessive false alarms.