First Alert has been making residential safety gear for decades, and the CO5120BN is a straightforward, no-nonsense carbon monoxide detector. The key differentiator here is the hardwired connection with a battery backup. That means it runs off your home’s electrical system but stays alive during a power outage. The electrochemical sensor is the gold standard for CO detection—it measures gas levels accurately rather than triggering from steam or cooking fumes. The built-in microprocessor helps keep false alarms to a minimum, which matters when you’re deciding whether to evacuate at 3 AM.

Installation is about as simple as it gets for a hardwired unit. The plug-in power connector clips into place without fussing with loose wires, and the tamper-resistant mounting bracket locks the alarm to the ceiling. The alarm itself is loud and clear at 85 decibels. It covers most standard bedrooms and hallways without issue. The battery backup uses a standard 9V battery, so you won’t be hunting for a specialty cell when it needs replacing.

One honest limitation: this is a bare-bones model. There is no digital display showing CO levels, no voice alerts, and no smart home connectivity. If you want app notifications or integration with Alexa, look elsewhere. But if you need a reliable, code-compliant detector that simply works and stays powered during a blackout, this is a solid choice. It does one thing and does it well.