How does air-drop detect other air-drop devices? It is clear from other posts that AirDrop "uses" Bluetooth Low Energy to "find" other AirDrop enabled devices. How does it do this? Specifically, how does an apple device differentiate between just another bluetooth device and one with airdrop enabled?

It could 1) try to pair with every transmitting device, 2) use the bluetooth friendly name, 3) additional data in the radio without pairing?

The BluetoothDeviceInfo structure that comes back from creating a radio on the Microsoft stack doesn't include any identifying info besides the Friendly Name: https://msdn.microsoft.com/en-us/library/windows/desktop/aa362924%28v=vs.85%29.aspx 

The other possibility is that it tries to pair with all broadcasting bluetooth devices - but that could be slow. 

Thanks for any help and/or insight!
I thought I would share what I found in case this information can shortcut someone else's learning.

Bluetooth Low Energy is a completely different Spec than older versions of bluetooth. There are completely different APIs from Microsoft to support BT LE: https://msdn.microsoft.com/en-us/library/windows/hardware/jj159880%28v=vs.85%29.aspx

Unlike older versions of bluetooth, a BT LE "Peripheral" device (sending device) can advertise it's capabilities so that a connecting device (Also known as a "Central") can tell what the Peripheral is capable of without actually connecting/pairing with the Peripheral.

The capabilities of a Peripheral are communicated using a Generic Attribute Profile, or GATT for short. 

Per my previous question, the BluetoothDeviceInfo structure is part of the older Microsoft API for bluetooth supporting non-BT LE devices: https://msdn.microsoft.com/en-us/library/windows/desktop/aa363058%28v=vs.85%29.aspx

Also, the C# 32feet.net library to help with Bluetooth does not support BT LE.

I hope that helps someone.