Automatic Logout after 15 minutes of inactive in php

Question

I want to destroy session if users are not doing any kind of activity on website. At that time after 5 users automatically redirect on index page. How is it possible? Is pos

Answer 1

                      session_start();
                      $t=time();
                      if (isset($_SESSION['logged']) && ($t - $_SESSION['logged'] > 900)) {
                      session_destroy();
                      session_unset();
                      header('location: index.php');
                      }else {$_SESSION['logged'] = time();}