PHP - Quiero saber como detectar usuario conectados a mi web

<?php

function getIP() {

	$ip="";

	if (getenv("HTTP_CLIENT_IP")) $ip = getenv("HTTP_CLIENT_IP");

		else if(getenv("HTTP_X_FORWARDED_FOR")) $ip = getenv("HTTP_X_FORWARDED_FOR");

		else if(getenv("REMOTE_ADDR")) $ip = getenv("REMOTE_ADDR");

		else $ip = "";

	return $ip;

}

function howManyIps() {

	$filename = "./howmanyip.log";

	$seconds = 300;

	$yourIP = getIP();

	if (file_exists($filename.".lock")) $readonly = true; else $readonly=false;

	$count = 0;

	//lock the file

	if (!$readonly) $fpLock = fopen($filename".lock", "w");

	//read data ips

	$fp = fopen($filename, "r");

	$arIPS=explode ("\n", fread($fp,filesize($filename)) );

	fclose($fp);

	//if file is locked get out

	if ($readonly) return count($arIPS);

	$s = "";

	$already=false;

	//update data and search user ip

	for ($i=0;$i<count($arIPS);$i++) {

		$arData= explode (" ", $arIPS[$i]);

		//update your user timer

		if ($yourIP==$arData[0]) {

			$already=true;

			$arData[1]=time();

		}

		// check if user is old

		if ( time()- (integer)$arData[1] < $seconds ){

			$s.=$arData[0]." ".$arData[1]."\n";

			$count++;

		}

	}

	if (!$already) {

		//your user is new, add it to the list

		$s.=$yourIP." ".time()."\n";

		$count++;

	}

	//save the list

	$fp = fopen($filename, "w");

	fwrite($fp,$s);

	fclose($fp);

	//remove thr lock

	fclose($fpLock);

	unlink($filename.".lock");

	return $count;

}

$usuariosConectados=howManyIps();

?>