How to used User agent in Codeigniter3.0.6?

I am testing with Codeigniter3.0.6 on User agent as below function then I try to testing IPhone, and Chrome inspect device mode but I got only number 1. I want to check if I view this website in Mobile phone it will echo number 2 if in PC browser echo number1 if can't detect browser show 0.

<?php
if (!defined('BASEPATH')) exit('No direct script access allowed');

class Main_Controller extends MY_Controller
{

    public $data = array();

    public function __construct()
    {
        parent::__construct();

        var_dump($this->CheckDevices());
        exit();

        $this->data['deviceType'] = $this->CheckDevices();
        if ($this->data['deviceType'] == 1) {
            $this->set_navigation();
        }
        elseif ($this->data['deviceType'] == 2) {
            retu false;
        }elseif($this->data['deviceType'] == 0){
            retu false;
        }
    }

    private function CheckDevices()
    {
        $this->load->library('user_agent');
        $agent = '';
        if ($this->agent->is_browser()) {

            $agent = 1;

        } elseif ($this->agent->is_mobile()) {

            $agent = 2;

        } else {

            $agent = 0;

        }
        retu $agent;
    }

    private function set_navigation()
    {
        $this->load->library('session');
        $this->load->library("nav_libs");
        retu $this->data['menus'] = $this->nav_libs->navigation();
    }
}

?>