Simply put, this is the first smoke and CO alarm that you don't want to hit with a hammer. Nest Protect is equally innovative for what it does, and what it doesn't do. It doesn't start chirping when its battery is low, sending you on a 2 AM, bleary-eyed search to figure out which alarm is making that awful noise. Nest Protect glows green whenever you first turn off the light in the area it's mounted, telling you that the battery level is good. When it starts getting low, Nest glows red. It can also send you reminders on your smartphone. And where traditional alarms can't differentiate between a brief trickle of smoke from the toaster or oven, Nest Protect will send a notification when it detects what appears to be standard cooking-related particulates, and only start blaring if the situation escalates to an actual fire.
In the case of an actual emergency, it can send alerts to your phone, as well as anyone else you've designated, such as a neighbor. And just as the Nest thermostat is still best in its class years after its debut, Nest Protect came out in 2013, and no one else has come close to matching or beating its ability to do its extremely important job, without aggravating the hell out of you. [$99; store.nest.com]