Then, when the alarm goes off, not only do you receive an audio alert—many include helpful voice instructions instead of just a siren—your smart phone also tells you what the problem is whether it’s smoke or CO, which alarm was activated, and sometimes even the severity of the smoke. Many smart smoke detectors hook into additional smart home gear and IFTTT, so you can get even more clever by having the lights start flashing if smoke has been detected, for example. Perhaps the biggest benefit of a smart smoke detector: No more hunting down midnight chirps, since you’ll also get phone based notifications about dying batteries. The Nest Protect is one of the most mature smart smoke alarms on the market, and it’s a no brainer of a choice if you want one of the most sophisticated and reliable smart smoke detectors out there. Alarms are varied, integrated lighting is color coded based on the type of threat, and the product includes helpful voice alerts when activated. In testing, our phone was alerted almost immediately, and the app couldn’t be simpler to master. If you have additional Nest gear at home such as a Nest thermostat things get even savvier, as you can configure the Protect to shut off your ventilation system if it detects smoke, a potential life saver. First is the concept of the smart battery: Rather than replace the entire alarm, a smart battery simply replaces the 9 volt cell inside your smoke detector. The battery contains a Wi Fi radio that can communicate with your home network and a companion smartphone app. The battery also includes a microphone that listens for the smoke alarm into which it has been installed. When the alarm goes off, the battery leaps into action and handles the “smart” side of things, working much like a standalone detector.