Have a Google sheets script run in the background

Question

I already have a script in place that sends out a notification when a new cell has been added to my spreadsheet. However, it only runs when I trigger it (through code editor) and does not run in the background. Essentially, I want to have this script run when something new is added to the spreadsheet, however, I'm unsure If this can be accomplished?

function sendNotification() {
      var ss = SpreadsheetApp.getActiveSpreadsheet();
      var sheet = ss.getActiveSheet();
  //Get Active cell
      var mycell = ss.getActiveSelection();
      var cellcol = mycell.getColumn();
      var cellrow = mycell.getRow();
  //Define Notification Details
      var recipients = "[email protected]";
      var subject = "THIS IS A TEST - Please Ignore "+ss.getName();
      var body = ss.getName() + " has been updated.  Visit " + ss.getUrl() + " to view the changes.";
  //Check to see if column is A or B to trigger
      if (cellcol == 1)
      {
  //Send the Email
      MailApp.sendEmail(recipients, subject, body);
      }
  //End sendNotification
  }

Thank you!