Following is a simple script, written in PHP, which will send an E-mail alert to you when one or more of your Web servers is inaccessible.
<?php
/* things to edit/change */
$fileToFetch = "isalive.txt";
$mailTo = "shekhar@it4enterprise.com";
$mailFrom = "alert@it4enterprise.com";
$websites = array(
"Website 1" => "http://www.website1.com",
"Website 2" => "http://www.website2.com",
"Website 3" => "http://www.website3.com"
);
/* end of things to edit/change */
foreach($websites as $name=>$value)
if(!($fp = @fopen($value."/".$fileToFetch,"r")))
mail($mailTo,"WEBSITE DOWN: ".$name,"WEBSITE DOWN: ".$name,"From: ".$mailFrom);
?>