The First Alert® SMCO210 Sealed 10-Year-Battery Combo Smoke and CO Alarm with Slim Profile Design uses our Precision Detection advanced sensing technology to meet the latest industry standards. This 2-in-1 alarm provides convenient protection against both fire and carbon monoxide (CO). The slim-profile combination alarm is half the depth of a standard alarm. It is sleek and compact to help the detector blend seamlessly with most home décor. And the 10-year lithium battery means no battery replacements for a decade – the end-of-life warning lets you know when it is time to replace the alarm. No more low-battery chirps and multiple battery replacements!