Hembisen’s 5-in-1 alarm combines natural gas and carbon monoxide detection into a single AC-plugged unit with a backup battery slot. That battery backup is the key feature here. If the power goes out—say, during a storm or an electrical fault—the device keeps running on a standard 9V battery (not included). It means you aren’t left guessing when you need it most.

The display shows real-time readings for CO (0-2000ppm) and explosive gases (0-10% LEL). You can adjust both the alarm volume and screen brightness across three levels, which is useful if you place it in a bedroom or a bright kitchen. The 85dB alarm is loud enough to wake you, but not painfully so. Four imported sensors handle detection, and the unit responds quickly to gas leaks or CO buildup.

One honest note: the 9V battery is sold separately, so factor that into your purchase. The ABS plastic housing feels sturdy, but the design is utilitarian—no sleek smart-home aesthetics here. It works reliably, does its job, and keeps monitoring even when the grid doesn’t.