only send a notification is server changes to status 'error'

app/Jobs/StatusChangeDetection.php

@@ -68,6 +68,11 @@ class StatusChangeDetection implements ShouldQueue
 
     public function sendNotificationIfRequired(StatusChange $change)
     {
+        // Only send a notification if server changes to status "error"
+        if ($change->status < \App\Status::ERROR) {
+            return;
+        }
+        
         $server = $change->server();
         $server_id = $server->id;
 

app/Sensor/Heartbeat.php

@@ -46,8 +46,9 @@ class Heartbeat extends \App\AbstractSensor
             $delta = \time() - $record->time;
         }
 
+        // > 15 minutes
         if ($delta > 900) {
-            return \App\Status::WARNING;
+            return \App\Status::ERROR;
         }
 
         return \App\Status::OK;