The Good: The new Nest Protect has a more refined design than the original model, as well a handy in-app alarm silence feature to go along with its already useful connected features and integration with other Nest products and IFTTT. The Bad: The history section in the app is empty and it doesn't have enough new features to justify an upgrade from the original. The Bottom Line: No other smoke and carbon monoxide detectors available today can match the second-gen Nest Protect in terms of looks and options, making it a great buy for anyone who appreciates design and connected features. Nest Labs apparently loves a good challenge. Its ability to transform boring, utilitarian household products into smart devices beautiful enough to make a design giant like Yves Behar weep (I imagine) is an incredible feat.And yet, Nest's original Protect smoke and carbon monoxide (CO) detector had a big problem. Its 'Wave' feature that literally let you turn off alarms with a gesture was deemed dangerously unreliable after it hit retail, leading to a recall.Now, a second-generation Protect has arrived and it's noticeably sleeker and smarter than its predecessor. With a slimmer profile, a new in-app "silence" button that allows you to turn off smoke and CO alarms remotely (the original Nest Protect doesn't currently support this feature) and integration with the Nest Learning Thermostat , Nest Cam and IFTTT, this $99\/\u00a389 detector is the best connected one we've seen yet. If you already have a first-gen Nest Protect, I'd skip this upgrade, but I strongly recommend the Protect 2.0 to first-time connected detector shoppers.Pretty, pretty ProtectMany consumers will still happily settle for the $25 puck of white plastic that functions as the traditional smoke detector. Like its predecessor, the second-generation Nest Protect elevates the aesthetic of the standard issue detector, but its balances that appeal with a set of connected features that let you control the Protect remotely via your mobile device or your account on the Nest Web page.As before, Nest nails the aesthetic upgrade, thanks to the Protect's white or black finish, square design with rounded edges, and a stainless-steel mesh cover that looks neat and gives smoke and CO a bunch of access points. You might not install it in a place at home where you will often get to admire its looks, but at least when you do, you'll appreciate seeing it.A ring of colorful LEDs surround the central on-off button, alerting you to the Protect's current status. It goes blue during setup or testing mode, green when everything's fine, white as an optional nightlight that illuminates when you walk underneath it, yellow\/orange to warn that there's a potential smoke or CO emergency and red when there's a real smoke or CO event.Beyond looksYou can use the second-gen Nest Protect even if you don't have Wi-Fi (or temporarily lose your Wi-Fi connection for some reason). Whether or not you have Wi-Fi, the Protect unit will issue a loud warning if it senses increasing smoke or CO levels (specifically, it will flash yellow\/orange and say, "Heads up. There's smoke\/CO.") And, if there's an emergency, it will flash red and say, "Emergency, smoke\/CO detected."The Protect will also test itself for low batteries or any other concerns regularly, communicate with any other Protects in the house (if one Protect alarm detects smoke, all of the Protects in the house sound) and display a faint white light when you walk underneath it in the dark -- presumably on your way to get a late night snack, a feature it calls Pathlight.To allow for of all of this functionality, the Protect has built-in sensors to detect electrochemical CO, heat, humidity, occupancy and ambient light, as well as a microphone. Nest also upgraded its smoke sensor with a split-spectrum sensor that's exclusive to the Protect 2.0. This new sensor claims to be better at detecting both slow- and fast-burning fires, which, unfortunately, wasn't something that we could test directly.With Wi-Fi, you can do a lot more, including naming your Nest Protect(s) hallway\/basement\/bedroom, etc., opting out of the Pathlight feature, receiving alerts and auto-updates to software, using the Nest Android or iOS mobile apps and Web app, pairing your Protect with the Nest Learning Thermostat, Nest Cam and select Dropcam models for advanced integrations and even accessing IFTTT for third-party automations with color-changing bulbs like those from Lifx and Philips Hue .Getting things goingI used an iPhone 6 Plus to set up my Nest Protect. Since I already had the Nest app, I simply opened the app, selected "Add product" and followed the simple steps to start testing out the full functionality of the unit.Given that the Protect has to be installed near your ceiling, it might take you a little longer than a typical plug-and-play smart-home device. I opted for a battery-powered model so I could test it in different locations; it comes with six Energizer Ultimate Lithium (L91) AA batteries. Installing the hard-wired version yourself (also $99), will also require a basic comfort level with home electrical systems. For the initial setup, it took me about 10 minutes from start to finish. As always, consult a professional if you have any installation questions or concerns.