Bluetooth 4, how do we take advantage of its low energy features?
Low Energy requires both ends to be updated. Apple has a knowledge base article explaining this at:


https://support.apple.com/en-us/HT202880 - iOS and iBeacon requirements


For Mac, open System Information and select the Bluetooth section on the left. If you have the following line towards the top, you are equipped for Low Energy bluetooth:


  Bluetooth Low Energy Supported: Yes


Magic Mouse 2, Magic Keyboard and Magic Trackpad 2 all support low energy bluetooth as well.