session expire

function check_session() {
    session_start();
    #set timeout period in seconds
    $inactive = 5400;
    #check to see if $_SESSION['timeout'] is set
    if (isset($_SESSION['timeout'])) {
        $session_life = time() - $_SESSION['timeout'];
        if ($session_life > $inactive) {
            session_destroy();
            header('Location: '.WWW_PATH.'public/login.php');
            exit;
        }
    }
    $_SESSION['timeout'] = time();
}