This is Nest's second-generation Protect smoke and carbon monoxide (CO) detector.
Both the wired and battery-powered units cost $99 in the US and £89 in the UK.
Hardware for installation is included in the packaging and outlined in the included instructions.
This new Protect has a slimmer, more rounded profile.
It also boasts an updated app.
The app allows for integrations with Nest's other products, the Nest Cam, the Nest Learning Thermostat and select Dropcam cameras.
The app gives you an at-a-glance look at the status of your home.
You can receive alerts about potential issues and even silence an alarm remotely from the app.
The unit itself also displays various colors that change depending on the device's current status.
The LED ring will glow blue during setup or tests; green when everything's fine; white as an optional nightlight that illuminates when you walk underneath it; yellow/orange warns that there's a potential smoke or CO emergency and red for a real smoke or CO emergency.