Your smoke alarms and carbon monoxide detectors might not be working properly—even if you never let their batteries run out or they are hardwired into your home’s electrical system. That’s because sensors in these alarms can fail over time.

To stay safe, replace a smoke alarm 10 years after its date of manufacture—an anniversary that can come sooner than 10 years after you installed the device depending on how old the smoke alarm was when you installed it.

For carbon monoxide detectors, check the manufacturer’s website for replacement details if this is not spelled out on the device and you no longer have its ­instructions.

Dates of manufacture typically are printed on the backs of smoke alarms and carbon monoxide detectors, so you might have to remove them from walls or ceilings to check them.

More than 20% of residential fire deaths occur in homes where there were smoke alarms but those alarms were not working properly, either because of expired batteries or nonfunctional alarms.

Replace an alarm before the 10-year mark if it continuously “chirps” or displays a flashing red light or if its alarm does not sound when you press the “test” button (when battery replacement is not the issue).

Smoke alarms can cost less than $10 apiece, and carbon monoxide detectors can cost less than $25, so there is little financial reason to continue using an older unit. Make sure that the new alarms you install have been approved by a recognized independent testing lab such as Underwriters Laboratories (look for the “UL” logo on the ­packaging).­­­­

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