Installing and maintaining smoke and carbon monoxide (CO) detectors can save your life. Luckily, they’re inexpensive and easy to install. Basic smoke detectors cost as little as $10, and carbon monoxide detectors cost as little as $20.
Newer models offer more features. For example, interconnected detectors communicate among devices and provide integrated, whole-house protection. With such a system, when one detects smoke or carbon monoxide all of them will sound—whether the detectors are hardwired or wirelessly connected.
How We Test Smoke and Carbon Monoxide Detectors
Each smoke and carbon monoxide detector that enters Consumer Reports’ labs is rigorously tested to make sure it keeps you and your family safe. For smoke detectors, we test response time to both flaming fires and smoldering, smoky fires. We’ve found that not all detectors can adequately detect both fire types.
We test carbon monoxide detectors against low CO levels (100 parts per million) and high CO levels (400 ppm). We also test the accuracy of their carbon monoxide measurements if they offer readings through a digital display or audio announcements.
Combination detectors go through both sets of tests. All these test results are then folded into our comprehensive smoke and carbon monoxide detector ratings.
Types of Smoke and Carbon Monoxide Detectors
You can find standalone smoke detectors and carbon monoxide detectors, as well as combination smoke and carbon monoxide detectors in smart and non-internet-connected forms. All three detector types offer standalone and interconnected varieties. Few combination detectors are effective at detecting carbon monoxide, smoldering fires, and flaming fires, which is why we recommend that consumers use a combination of detectors in their homes for complete protection.
Smoke Detectors
Fires burn differently: Some flare, some smolder. You’ll find three types of smoke detectors on the market, but only one is effective against both types of fire.
Ionization smoke detectors are best at detecting the small particles typical of fast, flaming fires. But in our tests, all tested poorly for detecting smoky, smoldering fires. Ionization units are prone to false alarms from burnt food and steam, so don’t mount them near a kitchen or bathroom.
Photoelectric smoke detectors are best at detecting the large particles typical of smoky, smoldering fires but poor at detecting fast, flaming fires. Photoelectric units are less prone to false alarms from burnt food, so they may be a better fit in kitchen areas.
Dual-sensor smoke detectors combine ionization and photoelectric technology to detect both flaming and smoldering fires, offering you the best protection and saving you the hassle of installing two separate smoke detectors. But you may still need to install carbon monoxide detectors, if appropriate for your home.
Carbon Monoxide Detectors
Carbon monoxide detectors use sensors to detect the presence of CO in your home. Some models include digital displays to show the level of CO they detect, and some can read out the CO level via audio announcements. Remember, carbon monoxide detectors do not detect smoke or explosive gases, such as natural gas, propane, and methane.
Combination Smoke and Carbon Monoxide Detectors
Combination detectors incorporate ionization or photoelectric technologies (a few use both) and carbon monoxide detection to protect against both smoke and CO. Both conventional (not internet-connected) and smart models are available.
Smart detectors offer additional features through a companion smartphone app. Features include smartphone alerts about smoke/CO (even when you’re not home) and low batteries, as well as the ability to hush alarms from your phone. Some models connect to the internet via WiFi; others require an additional bridge or hub, a standalone device that connects smart home products to the internet.
Where to Place Them Throughout Your Home
Smoke detectors are a must in all homes, and carbon monoxide detectors are needed for any home with fuel-burning appliances, such as a furnace, water heater, range, cooktop, or grill. Even those living in all-electric homes should install carbon monoxide detectors because CO can seep into the house from an attached garage or if a backup generator is used too close to your living quarters during a power outage.
You’ll need smoke detectors that detect flaming and smoldering fires for each bedroom, one outside each sleeping area, and at least one detector installed on each floor, including in a finished attic and in the basement. You should also have a carbon monoxide detector on each living level, outside each sleeping area, in the basement, and near (not inside) an attached garage.
Use the illustration below as a guide to where you need detectors, and tally up the number of smoke and carbon monoxide detectors you need to buy. Keep in mind that your home might need more or fewer detectors, depending on its size and number of rooms.
How to Shop for Detectors
1. Check Local Regulations
Before you shop, check regulations in your area. Your town or state might have specific requirements (you’ll need to know, say, when you sell your home) about what to use, including types of detectors and their placement. Also, some insurance companies offer a discount for homes with smoke detectors.
2. Pick a Power Source
Hardwired smoke and carbon monoxide detectors tie into your home’s wiring—professional installation is required—and usually have backup batteries. Battery-only detectors are the simplest to install, and they work during a power failure. Some models use removable batteries that require annual replacement, while others use sealed lithium batteries that last the life of the detector. Plug-in detectors are also available, but electrical outlets are typically located low on the wall, while the optimal placement for the detector is on or near the ceiling.
3. Smart or Not
Smart smoke and carbon monoxide detectors give you the advantage of knowing if something’s wrong when you’re not home, but they also come with a big price tag. We also haven’t found a smart smoke and CO detector that successfully does it all. But if you decide to outfit your home with this type, we recommend also installing additional dual-sensor smoke detectors. Smart detectors, whether hardwired or battery-powered, will also interconnect with other detectors of the same model.
4. Look for the UL Stamp
Check the detector packaging to make sure it meets the Underwriters Laboratories standard—look for the UL label. You should also look for the date of manufacture printed on the back of the detectors. Devices lose their sensitivity over time, so the fresher, the better. As a rule of thumb, replace carbon monoxide detectors every five years and smoke detectors every 10 years.
UL has also announced updates to its standards, which will require all manufacturers to make smoke detectors that can distinguish between smoldering fires and cooking smoke. It was originally supposed to go into effect by the end of June 2021, but it has now been delayed twice because of supply chain issues, with a new effective date of June 30, 2024. As part of Underwriters Laboratories’ updated standard, it is expected that manufacturers will no longer be able to make traditional, single sensor (photoelectric or ionization) smoke detectors.
5. The Truth About Interconnected Detectors
You can interconnect some smoke and carbon monoxide detectors so that all units in the house sound an alarm when any single one is triggered. Some newer homes may have wiring already in place to link the detectors. In a home without such wiring, you can buy detectors that interconnect wirelessly. These interconnected smoke and carbon monoxide detectors are an important safety feature in a home with multiple levels, although standalone detectors may be adequate for a small, single-level home.
While interconnected alarms can make your home safer, they have some limitations. In many cases interconnected alarms can interconnect only with models made by the same brand. In fact, Richard Roux, the National Fire Protection Association’s senior electrical specialist, told CR that you should always check with the manufacturer to see which specific models are compatible, even within the same brand, because some brands could change their interconnect system over time.
Despite the limitations, we recommend using interconnected detectors. They can make your home much safer by alerting you to danger before the fire or CO spreads throughout your home. Roux adds that interconnected alarms (whether hardwired or wireless) are also becoming a requirement in many states when you try to sell your home.
6. Consider Voice Alerts
Children tend to sleep more deeply than adults and might not awaken to a conventional alarm. Some smoke and combination smoke and carbon monoxide detectors use a voice command, but it’s not confirmed whether that’s the most effective way to wake children. According to one study, a greater percentage of children ages 6 through 12 awoke to the sound of their mother’s prerecorded voice than to a tone alarm.
7. Consider Your Security System
You can incorporate some smoke and carbon monoxide detectors into a security system that sounds an alarm outside and inside the house. Such systems may also have a monitoring service that can notify the police or fire department, or even call your cell phone.
Features You’ll Find
The latest smoke and carbon monoxide detectors have added features to better protect you and your family. Here’s what to consider when tailoring the safest combination of detector options to your household’s needs.
Battery Backup
A backup battery for hardwired smoke and carbon monoxide detectors offers security in case of a power failure. All battery-powered smoke and carbon monoxide detectors warn you when the battery is low. Some provide warning chirps, a low-battery voice message, or a visual display.
Smartphone Alerts From Smart Detectors
Smart smoke and carbon monoxide detectors connect to smartphone apps that can alert you when detectors go off, even if you’re not home. They will also let you know when batteries are running low, so you can avoid pesky chirping.
Digital Carbon Monoxide Display
This feature displays carbon monoxide concentrations in parts per million, even when the concentrations are below the level that triggers the detector. Carbon monoxide detectors certified by UL must go off at no less than 70 ppm, but lower amounts may harm heart patients. The display can alert you if the carbon monoxide 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 detectors, slightly more for smart detectors.
Hush Button
To silence a nuisance smoke detector, pressing a hush button is more convenient than disabling the unit, and it avoids the possibility of forgetting to turn it back on. All the smoke detectors we tested had this feature. Some carbon monoxide and combination smoke/CO detectors can work with a remote control to silence a nuisance alarm.
Safety and Strobe Lights
Some smoke detectors provide path illumination, a potential lifesaver in the dark. There are also alarms with strobe lights, which are the best warning for the hearing-impaired. Some smoke detectors have an integrated strobe light, and some accept add-on strobes.
Installation and Maintenance
Smoke and carbon monoxide detectors are protective only when installed correctly and if their batteries are replaced annually (unless they have a 10-year sealed lithium battery). Smoke rises, so mount smoke detectors on the ceiling or 12 inches below the ceiling on a wall. Test smoke and carbon monoxide detectors weekly, and vacuum them monthly. Follow the manufacturer’s recommendations regarding battery replacement. Replace carbon monoxide detectors every five years and smoke detectors every 10 years.