In recent years more states have enacted legislation or imposed regulations that require home sellers to install smoke and carbon monoxide detectors before selling a home. As of March 2018, more than two-thirds of states have such requirements and also mandate home inspections by fire officials to make sure the devices are installed correctly and in working order.

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Guidelines set by the National Fire Prevention Association (NFPA) call for nine smoke detectors and four carbon monoxide detectors for a typical three-bedroom, two-bathroom house with an attic and a basement. That means installing or replacing all these devices can add up fast.

But when it comes to safety, the cost is a relative bargain. You can get a good standalone smoke or CO detector for $30; connected models cost about twice that. So even if you’re installing 10 detectors or more to meet the regulations, it will cost well under $500. The bonus? You’ll be safer while still living in the house.

Even if home buyers are looking for a house in a state that doesn’t require smoke and carbon monoxide detector installations, it’s wise to follow the NFPA’s recommendations once you move in. Here’s what else you should know.

Check the Alarm's Pedigree

Every model that we score in our smoke and carbon monoxide detector ratings performs to the recommended safety standard. But the highest-scoring models alarm faster within a given time range. That’s crucial because in a span of only several minutes, a fire can reach its flashpoint—the point at which it becomes so hot it can set furnishings ablaze without even touching them. And carbon monoxide, a colorless, odorless gas, can kill you in minutes.

In addition to checking your alarms against our ratings, you can also look on the back of the device for a UL symbol—for Underwriters Laboratories—which indicates that it has been tested to a widely accepted safety standard.  

“Make sure your smoke and carbon monoxide detectors are certified by a third-party testing agency, such as UL or ETL,” says Bernie Dietrick, who oversees Consumer Reports’ testing of these safety devices. “In our most recent tests, we found two models of off-brand CO alarms purchased online that failed to alarm when exposed to dangerous levels of carbon monoxide.”

Check our smoke and CO detector buying guide for tips on where to place the devices.

Test the Batteries

This step is so obvious that it’s easy to skip, but according to the NFPA, nearly half of home fires that fail to trigger alarms occur in homes where batteries have expired or been removed from a smoke alarm. Even if the home you’re considering received a signoff from the fire department that the detectors are working, that inspection might have occurred months before the closing, during which the seller might have borrowed batteries from a detector to power the remote control. If so, you’ll want to know sooner rather than later. 

So once you’re settled in, check the batteries twice a year or as often as the instructions in the owner’s manuals recommend. A good reminder is to check the detectors when Daylight Saving Time begins in March and ends in November. 

Do You Want Real-Time Monitoring?

Many security companies now offer smoke and carbon monoxide detectors that are monitored in real time. If an alarm is triggered, the fire department will be sent to your home. So when buying a house, make arrangements with the seller to transfer the monitoring contract to your name, or sign up for the service yourself. 

If you don’t want to pay a monthly monitoring fee, consider installing a network of interconnected alarms. These pricier models trigger all the units in your home to sound when any detector senses smoke or carbon monoxide, which is particularly valuable if you’re asleep upstairs and there’s a carbon monoxide leak from your furnace in the basement. Our top-rated model, the First Alert OneLInk SCO501CN, is a battery-powered combination photoelectric smoke and carbon monoxide detector that wirelessly connects to multiple units.

But note that because photoelectric smoke detectors are best at detecting smoldering fires, you’ll want ionization alarms as well. They’re better at detecting fast, flaming fires. For more information, check our smoke and carbon monoxide alarm buying guide. No combination CO and smoke alarm currently on the market detects both types of fires and carbon monoxide. So you need all three devices—or if you opt for combination smoke and CO alarms, you'll want to buy standalone ionization alarms to detect rapidly-spreading fires, too. 

Smoke Detectors 101

Your life could depend on a smoke detector actually detecting smoke. On the "Consumer 101" TV show, Consumer Reports expert Bernie Deitrick explains to host Jack Rico what you need to know about these lifesaving devices.