Restricting user to one open tab in browser

Question

I had a requirement to restrict my web site's users to just one open tab in the browser. I am aware that this is not the best thing to do in terms of general user experience guidelines but its an internal application that doesn't play well with such a scenario so had to do it.

Following is what I came up with

function IsNewTab() {
  return $.cookie('TabOpen');
}

$(function() {
  if (!IsNewTab()) {
    $.cookie('TabOpen', "YES", {
      path: '/'
    });
    $(window).unload(function() {
      $.removeCookie('TabOpen', {
        path: '/'
      });
    });
  } else {
    alert('already some tab open')
      //OR
      //window.close()
  }
});

I'd like opinions on the above. Are there any loopholes (keeping in mind that the target audience isn't too technical and probably won't go hacking around with the browser console). Are there any possible improvements that can be made ?