MyUserAgentComponent として定義

以下ソース
class MyUserAgentComponent extends Component {
    private $ua;
    private $device;
    
    public function initialize(Controller $controller) {
        $this->controller = $controller;
    }

    public function set(){
        $this->ua = mb_strtolower($_SERVER['HTTP_USER_AGENT']);
        if(strpos($this->ua,'iphone') !== false){
            $this->device = 'mobile';
        }elseif(strpos($this->ua,'ipod') !== false){
            $this->device = 'mobile';
        }elseif((strpos($this->ua,'android') !== false) && (strpos($this->ua, 'mobile') !== false)){
            $this->device = 'mobile';
        }elseif((strpos($this->ua,'windows') !== false) && (strpos($this->ua, 'phone') !== false)){
            $this->device = 'mobile';
        }elseif((strpos($this->ua,'firefox') !== false) && (strpos($this->ua, 'mobile') !== false)){
            $this->device = 'mobile';
        }elseif(strpos($this->ua,'blackberry') !== false){
            $this->device = 'mobile';
        }elseif(strpos($this->ua,'ipad') !== false){
            $this->device = 'tablet';
        }elseif((strpos($this->ua,'windows') !== false) 
            && (strpos($this->ua, 'touch') !== false && (strpos($this->ua, 'tablet pc') == false))){
            $this->device = 'tablet';
        }elseif((strpos($this->ua,'android') !== false) && (strpos($this->ua, 'mobile') === false)){
            $this->device = 'tablet';
        }elseif((strpos($this->ua,'firefox') !== false) && (strpos($this->ua, 'tablet') !== false)){
            $this->device = 'tablet';
        }elseif((strpos($this->ua,'kindle') !== false) || (strpos($this->ua, 'silk') !== false)){
            $this->device = 'tablet';
        }elseif((strpos($this->ua,'playbook') !== false)){
            $this->device = 'tablet';
        }elseif((strpos($this->ua,'docomo') !== false)){
            $this->device = 'Ktai';
        }elseif((strpos($this->ua,'kddi') !== false)){
            $this->device = 'Ktai';
        }elseif((strpos($this->ua,'vodafone') !== false)){
            $this->device = 'Ktai';
        }elseif((strpos($this->ua,'softbank') !== false)){
            $this->device = 'Ktai';
        }else{
            $this->device = 'others';
        }
        return $this->device;
    }

}


[ Controller 側 ]   ※AppController が良いかも。

public $components = array("Session","MyUserAgent");
public function beforeFilter(){
    parent::beforeFilter();
    
    $ua = $this->Session->read("ua");
    if(!isset($ua)){
        $ua = $this->MyUserAgent->set();
        //初回以降は session から呼び出せる
        $this->Session->write("ua",$ua);
    }
}