CO & smoke alarms


CO & smoke alarms

CO & smoke alarm buying guide

Last updated: June 2015
Getting started

Getting started

Approximately 2,500 people are killed each year in residential fires, and another 500 die from carbon monoxide (CO), a colorless, odorless gas that's known as the "silent killer." Installing smoke and CO alarms throughout your home is the first step toward staying safe.

Every home should have smoke alarms, and CO alarms are a must in all homes with fuel-burning appliances such as a furnace, water heater, range, cooktop or grill. Even an all-electric home may benefit from a couple of CO alarms, because using a generator during a blackout produces CO. You need alarms that detect flaming and smoldering fires for each bedroom, with at least one set on each level, including the attic and basement. You should also have a CO alarm on each living level, in the basement, and near (not inside) an attached garage.

You can buy smoke and CO alarms at hardware and home-improvement stores and online. Smoke alarms are relatively inexpensive, starting at about $15 for basic models. CO alarms cost $35 and up. Check the package to make sure smoke alarms meet Underwriters Laboratories Standard 217 and CO alarms meet UL Standard 2034. Also look up the date of manufacture on the back of the alarms. These devices lose their sensitivity over time, so the fresher, the better. For performance data on specific models, see our Ratings of CO and smoke alarms.

None do it all

Our tests of two dozen alarms show that effective protection from fire and CO remains far too complicated. For example, smoke alarms that use ionization technology were great at detecting a fast, flaming fire such as burning paper, but poor at detecting a smoldering fire, as in a couch or mattress. The opposite was true of photoelectric smoke alarms. A few alarms combine ionization and photoelectric technologies to cover both types of fire, but they don't detect CO. And those that combine CO and smoke detection are effective for either type of fire, but not both. Our challenge to manufacturers: Produce a single device that senses both types of fire and CO.

Strength in numbers

Getting all of a home's alarms to communicate with one another poses another hurdle. Interconnected alarms all sound simultaneously when any one is triggered. Thus, they can warn you of a fire or CO leak in the basement when you're asleep upstairs. You can use adapters to connect hard-wired alarms, even those made by different manufacturers. But wireless alarms can communicate only with other wireless alarms of the same make, since manufacturers use different frequencies. The industry needs to fix that problem as well.

Do your homework

Before you shop, check your town's or county's regulations. Details such as types of alarms and placement differ from one jurisdiction to another. Also contact your insurance company. Some insurers offer a 5 percent discount for homes with smoke alarms.

Proper installation and maintenance are critical

Follow the instructions in the owner's manuals. A few rules of thumb: Smoke rises, so mount smoke alarms on the ceiling or high on the wall. To avoid false alarms, don't mount ionization smoke alarms in the kitchen, where burnt toast might set them off, or near sources of steam such as a bathroom, laundry room, or sauna. Don't install CO units in the kitchen or near any cooking appliance, in the garage, or near the furnace or water heater. And avoid breezy areas-around fans, vents, air conditioners, doors, and open windows, where fresh air can cause a misleadingly low CO reading. Keep CO alarms out of direct sunlight.

Test smoke and CO alarms weekly and vacuum them monthly. Follow the manufacturer's recommendations on battery replacement. Alarms have a limited useful life. Replace CO alarms every five years and smoke alarms every 10 years. In addition, prepare a plan of evacuation in case of a fire or CO emergency, and have everyone in the family practice it like a fire drill every few months.


Although none of the smoke or CO alarms we tested did everything well individually, you can combine various types for optimal protection. Here are the types of alarms to consider.

CO alarms

We found wide variations in performance, with some models responding almost twice as quickly as others in our tests. But any CO detector is better than none at all.

Ionization smoke alarms

The ones we tested were all excellent at detecting the small particles typical of fast, flaming fires, but all were poor at detecting smoky, smoldering fires. Ionization units are generally prone to false alarms from burnt food and steam, so don't mount them near a kitchen or bath.

Photoelectric smoke alarms

The ones we tested were all excellent at detecting the large particles typical of smoky, smoldering fires, but all were poor at detecting fast, flaming fires. Photoelectric units are less prone to false alarms from burnt food and steam, so you can use them around the kitchen or bath.

Dual-sensor smoke alarms

These combine ionization and photoelectric technology to save you the hassle of installing two separate smoke detectors. All the ones we tested were excellent at detecting smoldering and flaming fires. But you'll still need separate CO units.

Combination smoke/CO alarms

These can detect smoke as well as CO. But those we tested were excellent at detecting either a flaming or a smoldering fire, but not both. If you buy a combination CO and ionization alarm, we recommend that you also get a separate photoelectric unit, or vice versa.


The latest smoke and CO alarms have some new features to better protect you and your family. Here are the smoke and CO alarm features to consider.

Power source

Hard-wired smoke and CO alarms tie into your home's wiring and require professional installation. Battery-only alarms are simple to install, and they work during a power failure, but most batteries require yearly replacement. Lithium batteries may last the life of the alarm. There are also plug-in smoke alarms. The drawback there is that electric outlets are typically low on the wall, while the optimal placement is on or near the ceiling.

Battery backup

A backup battery for hard-wired smoke and CO alarms offers security in case of a power failure.

Low-battery warning

All battery-powered smoke and CO units warn you when the battery is low. Some provide warning chirps, a "low battery" voice message, or a visual display.


You can link some smoke and CO alarms so that all go on when any one is triggered. If a fire starts or CO rises to an unsafe level anywhere, the alarms will alert people throughout the house. Some newer homes have wiring already in place to link the alarms. In a home without such wiring, you can buy alarms that interconnect wirelessly. Interconnecting alarms are a vital safety feature in a home with multiple levels. A standalone alarm may be adequate for a small, single-level home.

Digital CO display

This important feature displays CO concentrations in parts per million, even when the concentrations are below the level that triggers the alarm. CO alarms certified by UL must go off at no less than 70 ppm, but as little as 30 ppm may harm heart patients, pregnant women, and children. The display can give you an early heads up if the CO level is inching up or is higher than usual. Some also show the peak level since they were reset, warning you of any spikes that occurred while you were away. Expect to pay a little extra for this feature: $5 or $10 for standalone units, slightly more for units that can be interconnected.

Hush button

To silence a nuisance smoke alarm, pressing a hush button is more convenient than disabling the unit, and it precludes the possibility of forgetting to turn it back on. All the smoke alarms we tested had this feature.

Strobe alarm

Strobe lights are the best warning for the hearing impaired. Some smoke alarms have an integral strobe light, and some accept add-on strobes.

Voice alarm

Children tend to sleep deeper than adults and may not awaken to a beeping sound. Some smoke and combination CO/smoke alarms use a voice command, but it's not clear whether that's the most effective way to wake children. According to one study, many pre-teenagers who slept through tone alarms awoke to the sound of their mother's prerecorded voice. But more research is needed.

Remote-control mute

Some CO and combination CO/smoke alarms can work with a remote control to silence a nuisance alarm.

Safety lights

Some smoke alarms provide path illumination, a plus in the dark.

Overall security system

You can incorporate some smoke and CO detectors into a system that sounds an alarm outside and inside the house. It can also have a monitoring service notify the police or fire department or even call your cell phone.


The two major manufacturers of carbon monoxide (CO) alarms are First Alert and Kidde, representing three-quarters of the market. These alarms use electrochemical-sensing technology, currently the most reliable technology for carbon monoxide. Purchases of battery operated units versus hardwired units were 58 percent versus 42 percent in 2007, respectively. That is because battery-operated units are easier to install.

First Alert and Kidde are also the major players in the smoke alarm industry. Smoke alarms use either ionization or photoelectric sensing technology to detect fast-flaming or smoldering fires, respectively.

First Alert

First Alert owns the BRK branded units, and the ONELINK line of wireless, talking units. Product offerings include plug-in, battery, hardwired, and hardwired with battery-backup units. Carbon monoxide units range from $20 to $100. First Alert also offers combination units that detect carbon monoxide and smoke.

These combo units use electrochemical and photoelectric technologies. First Alert is available at Home Depot, Lowes, Walmart, Target, and at food and drug stores.

Smoke alarm prices range from $13 to $100. Product offerings include dual sensor units, which combine ionization and photoelectric technologies.


Kidde owns FireX branded units and offers the Nighthawk and Silhouette lines. Nighthawk comes in plug-in and battery operated units. Price range of carbon monoxide units is $20 to $70. The Silhouette line comes in hardwired units and features a sealed, self-charging lithium battery that lasts for the life of the unit. The units can interconnect with other units and retail for about $60. Kidde also offers combo units, which have a smoke detector feature in addition to the carbon monoxide detector.

Kidde also carries the Intelligent alarm (not tested), which uses one device to detect fast flaming and smouldering fires and carbon monoxide. A voice warning is issued based on what danger is detected. CO alarms are sold in home improvement stores, including Home Depot and Lowes,  at Sears, and at food and drug stores.

Smoke alarm prices range from $10 to $70. Kidde makes dual sensor units that use ionization and photoelectric technologies.

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