iMore:

Want to be able to unlock your Mac using Touch ID? Now you can. What’s more, it’s free for the next two days.

Beginning March 16th, the MacID iOS app is free, but only for 48 hours. It’s normally $4. It’s an app for your Touch ID-based iOS device, and it works in conjunction with a second app that you install on your Mac. MacID lets you lock your Mac with a swipe of the finger on your Touch ID-equipped iPhone or iPad.

Doesn’t work with my 2011 Macbook Pro but should work on Macs that are capable of using Bluetooth LE.