5 stars following more than 320 reviews at Home Depot, where this smoke alarm is sold as the Code One 21010019. This is a single unit, and is sold under both the First Alert and BRK brands. It's also available in a two pack as the First Alert SA511CN2 3ST Est. $70, and that's the version that actually gets the most feedback. For example, at Amazon it earns a score of 4. 1 stars following more than 320 reviews. Wirecutter does not test the smoke alarm, and hence its evaluation isn't relied on in making our selection. That said, based on their own research, Doug Mahoney calls the SA511CN2 3ST the best basic smoke alarm. The feedback on the SA511B is even better, albeit more limited: 4. 7 stars at Amazon, 4. 6 stars at Home Depot, but that's only based on around 20 reviews across the two sites.