Maybe you own an Apple Watch and you waited for the feature to unlock your Mac with your watch in macOS Sierra. Now you recognized that your Mac is not supported for this feature in macOS Sierra, as my model is.
I still use a MacBook Pro mid 2012, which I tweaked with 16GB RAM and 600GB SSD. So there is no need to buy a new computer all the time. I was really upset, when I figured out that macOS Sierra does not support my model. When I searched for „best apps for Apple Watch“, I fortunately found „Knock“. With a helper on your Mac, you can get this missing feature. Be sure to check the list of supported computers before buying the software! Read carefully through the app description.
At least for me this was a 5 star decission