ExtJS (2.2.1): making keypress event work

This doesn't work for me:

listeners:{
     keypress: function(field, e){
     alert("kp");
}

this one works just fine:

listeners:{
        'render': function(c) {
          c.getEl().on('keypress', function() {
               alert("kp");
      }, c);
        }
}

Source:
http://www.extjses.com/mensaje7282.html