CUser::IsOnLine

static function IsOnLine($id, $interval = null)
{
	global $DB;

	$id = intval($id);
	if ($id <= 0)
	{
		return false;
	}

	if (is_null($interval))
	{
		$interval = CUser::GetSecondsForLimitOnline();
	}
	else
	{
		$interval = intval($interval);
		if ($interval <= 0)
		{
			$interval = CUser::GetSecondsForLimitOnline();
		}
	}

	$dbRes = $DB->Query("SELECT 'x' FROM b_user WHERE ID = ".$id." AND LAST_ACTIVITY_DATE > DATE_SUB(NOW(), INTERVAL ".$interval." SECOND)");
	return $arRes = $dbRes->Fetch()? true: false;
}