Combination plug-in alarm provides 3‑in‑1 protection by detecting carbon monoxide, propane, and natural/methane gas using advanced electrochemical sensing. Backlit digital display shows current and peak CO levels, while status LEDs and a single test/silence button make operation straightforward. Unit plugs into any standard AC outlet and includes a 9V battery backup to maintain protection during power outages, sounding an 85 dB alarm for hazardous conditions. | First Alert | | Plug-in Electrochemical Explosive Gas and Carbon Monoxide Detector | Best Buy