Sample Bluetooth printing from Unity

BluetoothTest.cs

        var devices = DeviceInformation.FindAll(RfcommDeviceService.GetDeviceSelector(RfcommServiceId.SerialPort));
        var deviceInfo = devices[0]; // this makes some assumptions about your paired devices so really the results should be enumerated and checked for the correct device
        var device = BluetoothDevice.FromDeviceInformation(deviceInfo);
        var serResults = device.GetRfcommServices(BluetoothCacheMode.Cached);
        foreach(RfcommDeviceService serv in serResults.Services)
        {
            if(serv.ServiceId == RfcommServiceId.SerialPort)
            {
                var stream = serv.OpenStream();
                byte[] buff = System.Text.Encoding.ASCII.GetBytes("Testing\r\n");
                stream.Write(buff, 0, buff.Length);
                stream.Flush();
                stream.Close();
                break;
            }
        }