Smoke & Carbon Monoxide Detector Buying Guide

Smoke detectors are a must in any home, and carbon monoxide detectors are a necessity in any home with fuel-burning appliances, such as a furnace, water heater, range, cooktop, or grill. If you live in an all-electric home, a CO detector can protect you from garage mishaps or a backup generator placed too close to your living quarters during a power outage.

You’ll want smoke detectors that detect flaming and smoldering fires inside each bedroom, plus one outside each sleeping area, and at least one detector on each floor, including a finished attic and a basement. And you should also have a carbon monoxide detector inside each bedroom, outside each sleeping area, and on each level of your home, plus one near (not inside) an attached garage.

The illustration below can help guide you through the number you need and proper placement. Keep in mind that your home might require more or fewer detectors, depending on its size and the number of rooms.

1. Look for the UL Certified Stamp

Most critically, check the packaging for a UL or ETL certification label, which means the model has been properly tested and meets the voluntary UL safety standard for either smoke or CO detection. Manufacturers that certify their devices to UL standards will clearly say so. The risk of purchasing an uncertified and potentially faulty detector is highest when shopping on third-party sites on online marketplaces.

2. Pick a Power Source

Hardwired smoke and CO 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 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. Decide on Smart or Not

Smart smoke and CO detectors can notify you by text if something’s wrong when you’re not home and let you know when to replace the batteries. Many can also be integrated into larger smart home systems and interconnect with other detectors in your home.

4. Look for Interconnected Detectors When Available
You can link some smoke and CO detectors so that all units in the house sound an alarm when any one of them is triggered, which can be particularly useful in a multi-level home. Some newer homes may have wiring already in place to link them. In a home without such wiring, you can buy detectors that interconnect wirelessly.

In many cases, interconnected alarms only work in unison with models from the same brand. To be safe, always check with the manufacturer to see which models are compatible, even within the same brand.

6. Consider Voice Alerts
Some smoke detectors and combination smoke and carbon monoxide detectors use a voice command instead of a conventional alarm, which may help rouse those who sleep deeply.

7. Consider Your Security System
Some smoke and CO detectors can be linked in a security system that sounds an alarm both inside and outside the house. Systems such as Ring Alarm even let you utilize existing detectors by adding an alarm-listening device that triggers the security system when it “hears” your detectors go off. These systems may also have a monitoring service that can notify the police or fire department, or call your cell phone.

8. Check Local Regulations

Be sure to check the regulations in your area. Your town or state might have specific requirements about which detectors to use and proper placement. You’ll need to know that info when, say, you sell your home. Also, some insurance companies offer a discount for homes with smoke detectors.

9. Check the manufacturing date.

This should be printed on the back of the detector. Devices lose their sensitivity over time, so the fresher, the better. As a general rule, replace carbon monoxide detectors every five years and smoke detectors every 10 years.

Smoke and CO detectors protect only when they’re installed and maintained correctly.

• Smoke rises, so mount smoke detectors on the ceiling or 12 inches below the ceiling on a wall.
• Test smoke and CO detectors weekly.
• Vacuum detectors monthly, as dust can damage the devices and trigger false alarms.
• Batteries should be replaced annually, unless the detector has a 10-year sealed lithium battery. Follow the manufacturer’s recommendations regarding battery replacement.
• Replace carbon monoxide detectors every five years and smoke detectors every 10 years. 

Each smoke and CO detector that enters CR’s labs is rigorously tested to make sure it will keep you and your family safe. For a smoke detector, we test response time to both flaming fires and smoky, smoldering fires. Historically, not all detectors have adequately detected both, though many now come equipped with multiple sensors to help with that.

We test CO detectors at lower CO levels (70 ppm, in line with the alarm threshold for the UL 2034 certification standard) and high CO levels (400 ppm). We also test the accuracy of the CO measurement if the device offers readings via a digital display or an audio announcement.

Combination detectors go through both sets of tests. We then fold all results into our comprehensive smoke and carbon monoxide detector ratings. (Ratings of lifesaving products like these are available to everyone free of charge.)