Use this Bookmarklet to start monitoring a page for changes. When a page change is detected you will receive an alert notifying the changes

pageChangesNotifier.js

javascript:(function(){
 /*@author Pablo Cantero - http://pablocantero.com/blog/2010/09/15/javascript-para-notificar-se-o-site-teve-alteracoes*/
 var xmlHttp = getXMLHttpObj();
 if(xmlHttp == null){
 	alert('Failed to load XMLHTTP');
 	return;
 }
 var actual = getPageContent(xmlHttp, window.location.href);
 var intervalId = window.setInterval(function(){
	 var current = getPageContent(xmlHttp, window.location.href);
	 if(actual != current){
	 	alert('This page has been modified since you opened it');
	 	window.clearInterval(intervalId);
	 }
 }, 1000);
 function getPageContent(xmlHttp, url){
	 xmlHttp.open('GET', window.location.href, false);
	 xmlHttp.send('');
	 return xmlHttp.responseText;
 }
 function getXMLHttpObj(){
 	if(typeof(XMLHttpRequest)!='undefined')
	 return new XMLHttpRequest();
	 var axO=['Msxml2.XMLHTTP.6.0', 'Msxml2.XMLHTTP.4.0',
	 'Msxml2.XMLHTTP.3.0', 'Msxml2.XMLHTTP', 'Microsoft.XMLHTTP'];
	 for(var i = 0; i < axO.length; i++){
	 try{
	 	return new ActiveXObject(axO[i]);
	 }catch(e){}
	 }
 return null;
 }
})()