Consumer Reports says that the first generation Nest Protect worked well as a CO detector, though it was more effective in sounding an alarm when it spots high CO concentrations than low. User reviews, once mixed, are now much stronger as the product has been updated and tweaked since release. It currently earns a 4. 6 star rating following nearly 6,000 reviews at Amazon. While there are other smart smoke detectors available, none that we spotted have received the positive feedback that we saw for the Nest Protect. For example, the First Alert OneLink Est. $110 looks to directly compete with the Nest, but both expert and user reviews are underwhelming. Among other issues, both CNET and Wirecutter note shortcomings in the connected features, including slow response times pushing notifications to the iOS only app and for the app to silence a nuisance alarm. Reviewers hold hope that software improvements will eventually make the OneLink a contender, but for now, as Wirecutter notes, "many of the Onelink's features are just pale imitations of the Protect's offerings. "We also saw a little expert buzz around the Halo Smart Smoke and CO Alarm Est. $130, a hardwired smart smoke and CO detector.