<?php

$user_agent = "Mozilla/5.0 (Linux; Android 4.4.2; SAMSUNG-GT-I9505 Build/KOT49H) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2272.96 Mobile Safari/537.36";

preg_match('/Android ([\d\.]+)/im', $user_agent, $matches);
$version = $matches[1];

echo $version;