Via Merchant
Google’s Nest Protect brings the most comprehensive range of features at $119 per unit. It includes a CO detector and real-time alerts, as well as voice and color-coded signals to identify threat type and interconnected alarms (which don’t require WiFi). It also offers hardwire and battery-powered options, and a Split-Spectrum Sensor that detects both slow and fast-burning fires.
Make sure to use the recommended lithium batteries; standard ones will drain quickly. Note that it isn’t fully integrated with Google Home, which means you’ll probably need to use the Nest app with it instead.
Via Merchant
First Alert’s OneLink Safe & Sound includes many of the features of the Nest Protect, plus a built-in AirPlay 2 speaker for music, which can be voice-controlled with Alexa. Highlights include a CO detector, real-time alerts, room-specific voice alerts, color-changing LED, wireless connection with other OneLink alarms, backup battery-strength monitor and built-in night light with adjustable brightness.
It connects to your smartphone via Bluetooth to Apple HomeKit and Amazon Alexa, although with Alexa the alarms won’t trigger Routines. It also works when not connected to a smart-home hub.
Downsides include no early warning option, no battery self testing (although you can test it through the app), no battery-only option (just hardwire), no ionization detector and a hefty $265 list price. Note: These are sometimes sold deeply discounted.