if let bluetoothDevice = IOBluetoothDevice(addressString: "Bluetooth Device ID")
{
    if !bluetoothDevice.isPaired() || !bluetoothDevice.isConnected() { continue }
    // Device is connected and paired, everything works fine until here.
    if bluetoothDevice.isHandsFreeDevice
    {
       // This line will also be executed, so the device supports the HFP.
       let handsFree = IOBluetoothHandsFree(device: bluetoothDevice, delegate: self)
       // handsFree?.connect()
       // Swift.print(handsFree?.isConnected) // returns false.
       let batteryValue = handsFree?.indicator(IOBluetoothHandsFreeIndicatorBattChg)
       Swift.print(batteryValue) // Always returns zero, can't be true.
       Swift.print(handsFree?.outputVolume) // Always returns 0.5.
    }
}

extension Controller : IOBluetoothHandsFreeDelegate
{
    func handsFree(_ device: IOBluetoothHandsFree!, disconnected status: NSNumber!)
    {
        Swift.print("disconnected")
    }

    func handsFree(_ device: IOBluetoothHandsFree!, scoConnectionClosed status: NSNumber!)
    {
        Swift.print("scoConnectionClosed")
    }

    func handsFree(_ device: IOBluetoothHandsFree!, scoConnectionOpened status: NSNumber!)
    {
        Swift.print("scoConnectionOpened")
    }

    func handsFree(_ device: IOBluetoothHandsFree!, connected status: NSNumber!)
    {
        Swift.print("connected status: " + status.description)
    }

    func handsFree(_ device: IOBluetoothHandsFreeDevice!, batteryCharge: NSNumber!)
    {
        Swift.print("batteryCharge: " + batteryCharge.description)
    }
}