On iOS it still uses multi-association wifi for the actual sharing, but it uses Bluetooth LE for the discovery. That allows it to be active at all times, which

On iOS it still uses multi-association wifi for the actual sharing, but it uses Bluetooth LE for the discovery. That allows it to be active at all times, which is very important given that on iOS most of the time AirDrop will be initiated while the app receiving the drop is completely inactive. Just tested this, and my iPad doesn't show up until I open the "control panel". Still it'll save battery by using only bluetooth for the initial scan.