MY_Exceptions.php

<?php
class MY_Exceptions extends CI_Exceptions {
  
    function My_Exceptions()
    {
        parent::CI_Exceptions();
    }

    function log_exception($severity, $message, $filepath, $line)

    {   
        $CI =& get_instance();
        $severity = ( ! isset($this->levels[$severity])) ? $severity : $this->levels[$severity];

    		log_message('error', 'Severity: '.$severity.'  --> '.$message. ' '.$filepath.' '.$line, TRUE);

        if($CI->config->item('base_url') == 'http://www.production-domain.com/') { 
          $CI->load->library('email');
          
          $uri = $CI->uri->uri_string();
          
          $CI->email->from('error-donotreply@YOURAPP.com', 'APP Error');
          $CI->email->to('youremail@example.org');

          $CI->email->subject('APP Error [severity: '.$severity.']');
          $CI->email->message('Severity: '.$severity.'  --> '.$message. ' '.$filepath.' '.$line."\n"."From URL: ".$uri);

          $CI->email->send();
        }
    }
}
?>

This might be a slightly better approach:

https://gist.github.com/2292191