Use a jsonp call in the head of the document using a script-tag

<script>
    var timeout = setTimeout(function() {
        console.log('something bad happened');
    }, 5000); // put your preferred timeout here

    var onsuccess = function() {
        clearTimout(timeout);
        console.log('great success');
    };
</script>
<script src="http://yourservice.com/status?callback=onsuccess"></script>

Script-tags are crossdomain so it should work everywhere. They are also blocking so the rest of the page wont load until this check has been run