[BirdOPrey5]

In a plugin on global_start add this code

include('includes/functions_forumlist.php'); 
global $vbulletin, $lastpostarray;

// call fetch_last_post_array() first to get last post info for forums
cache_ordered_forums(1);
if (!is_array($lastpostarray))
{
	fetch_last_post_array(-1);
}

   $forumidx = 999;  //Set your forum id to check here

   $lastpostinfo = (empty($lastpostarray[$forumidx]) ? array() : $vbulletin->forumcache["$lastpostarray[$forumidx]"]);
   $forumx = $vbulletin->forumcache["$forumidx"];

   $isnew = fetch_forum_lightbulb($forumidx, $lastpostinfo, $forumx);

   if ($isnew == "new")
  {
          //Execute code here if the forumid chosen above contains new posts
        



  }

Replace 999 with the forumid of the forum (or category) you want to check

This works for me, I repeat this code multiple times in the plugin to check multiple forumids-

   $forumidx = 998;  //Set your forum id to check here

   $lastpostinfo = (empty($lastpostarray[$forumidx]) ? array() : $vbulletin->forumcache["$lastpostarray[$forumidx]"]);
   $forumx = $vbulletin->forumcache["$forumidx"];

   $isnew = fetch_forum_lightbulb($forumidx, $lastpostinfo, $forumx);

   if ($isnew == "new")
       {
          //Execute code here if the forumid chosen above contains new posts
        



       }