Bluetooth pairing without user confirmation
Can I pair two devices over Bluetooth without a need to confirm this in user interface, accept to pair this devices. Can I exchange some extra data over, for example NFC, and then safely pair those two devices over Bluetooth without any extra user action?
Answer
This need is exactly why createInsecureRfcommSocketToServiceRecord() was added to BluetoothDevice starting in Android 2.3.3 (API Level 10) (SDK Docs)...before that there was no SDK support for this. It was designed to allow Android to connect to devices without user interfaces for entering a PIN code (like an embedded device), but it just as usable for setting up a connection between two devices without user PIN entry.
The corollary method listenUsingInsecureRfcommWithServiceRecord() in BluetoothAdapter is used to accept these types of connections. It's not a security breach because the methods must be used as a pair. You cannot use this to simply attempt to pair with any old Bluetooth device.
You can also do short range communications over NFC, but that hardware is less prominent on Android devices. Definitely pick one, and don't try to create a solution that uses both.
Hope that Helps!
P.S. There are also ways to do this on many devices prior to 2.3 using reflection, because the code did exist...but I wouldn't necessarily recommend this for mass-distributed production applications. See this StackOverflow.