gistfile1.txt

// ==UserScript==
// @name  JIRA Issue Change Notifier
// @include       https://jira.example.com/browse/*
// ==/UserScript==

var checkInterval = 5000;
var issueKey = JIRA.Issue.getIssueKey();
var updatedDate = new Date(jQuery('span#updated-date time')[0].dateTime).getTime()

var isIssueUpdated = function() {
  jQuery.ajax({
    dataType: 'json',
    url: "/rest/api/2/search?jql=updated > " + updatedDate + " and issue=" + issueKey + "&maxResults=0",
    success: function(data) {
      if ( data.total != 0) {
        jQuery('.aui-page-header').css('background-color', 'red');
      } else {
        setTimeout(isIssueUpdated, checkInterval)
      }
    },
    error: function() {
      setTimeout(isIssueUpdated, checkInterval)
    },
    timeout: 10000,
  });
}

isIssueUpdated();