If you would like to see it in all dashboards tabs you could use my flow as a base, then place an hidden template node in all tabs (in template node options place it in the body and not in the head section because if in the head it cannot receive msg inputs) in that template just set up the template node to watch for the input:
<script>
(function(scope) {
scope.$watch('msg.payload', function(data) {
// get the element from the dashoard header and change its status using normal js/html
var elem = document.getElementById("headerStatus")
elem.className = data.payload ? 'online' : 'offline';
});
})(scope);
</script>
