How do I Send and Recieve data Simultenously

 using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.IO.Ports;

namespace Securino
{
    public partial class Form1 : Form
    {
        SerialPort port = new SerialPort();
        
        public Form1()
        {

            InitializeComponent();
            port.PortName = "COM2";
            port.BaudRate = 9600;
            port.Open();
           // listen();
                  
        }

        private void button1_Click(object sender, EventArgs e)
        {
            port.Write("l");
            
        }

        private void button2_Click(object sender, EventArgs e)
        {
            port.Write("r");
        }

        private void button3_Click(object sender, EventArgs e)
        {
            port.Write("f");

        }

        private void button4_Click(object sender, EventArgs e)
        {
            port.Write("o");
        }

        private void button5_Click(object sender, EventArgs e)
        {
            port.Write("c");
        }

        private void button6_Click(object sender, EventArgs e)
        {
            port.Write("x");
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            
        }

        private void button7_Click(object sender, EventArgs e)
        {
            
            Console.WriteLine("listening");
            int ch = port.ReadChar();
            if (ch == 65)
            {
                MessageBox.Show("INTRUDER DETECTED");
            }
        }
        }
        

        
    }