问C# IMEI检测任何通过U盘连接的设备

EN

private string GetIMEINumber(string PortName) //Serial
{
    string key = "";
    SerialPort serialPort = new SerialPort();
    serialPort.PortName = PortName;
    serialPort.BaudRate = 9600;
    try
    {
        if (!(serialPort.IsOpen))
            serialPort.Open();
        serialPort.Write("AT\r\n");
        Thread.Sleep(3000);
        key = serialPort.ReadExisting();
        serialPort.Write("AT+CGSN\r\n");
        Thread.Sleep(3000);
        key = serialPort.ReadExisting();
        serialPort.Close();
        string Serial = "";
        for (int i = 0; i < key.Length; i++)
            if (char.IsDigit(key[i]))
                Serial += key[i];
        return Serial;
    }
    catch (Exception ex)
    {
        MessageBox.Show("Error in opening/writing to serial port :: " + ex.Message, "Error!");
        return "";
    } 
}