Excluir outras referencias para mobile dentro da pasta de js, css, html, etc.
Atencao para o opera-mobile: Nos testes, o opera mobile emulator (rodando no windows) nao foi reconhecido como mobile


1.a) Javascript Simples

if( navigator.userAgent.match(/Android/i)
 || navigator.userAgent.match(/webOS/i)
 || navigator.userAgent.match(/iPhone/i)
 || navigator.userAgent.match(/iPad/i)
 || navigator.userAgent.match(/iPod/i)
 || navigator.userAgent.match(/BlackBerry/i)
 || navigator.userAgent.match(/Windows Phone/i)
 || navigator.userAgent.match(/ZuneWP7/i)
 ){
 // some code..
}

-------------------------------------------------

1.b) JavaScript Simples
function is_mobile() {
    var agents = ['android', 'webos', 'iphone', 'ipad', 'blackberry', 'Windows Phone', 'ZuneWP7'];
    for(i in agents) {
        if(navigator.userAgent.match('/'+agents[i]+'/i')) {
            return true;
        }
    }
    return false;
}

1.b.etc) Outra opcao

if( navigator.userAgent.match(/Android/i) || navigator.userAgent.match(/webOS/i) || navigator.userAgent.match(/iPhone/i) || navigator.userAgent.match(/iPad/i) || navigator.userAgent.match(/iPod/i) || navigator.userAgent.match(/BlackBerry/i) ){
	//Action
}

-------------------------------------------------

2) JavaScript incorporado

// Web Site: http://www.mobileesp.com
// Source Files: http://code.google.com/p/mobileesp/
// http://code.google.com/p/mobileesp/source/browse/
// http://code.google.com/p/mobileesp/source/browse/JavaScript/mdetect.js

<script type="text/javascript" src="mdetect.js"></script>
<script type="text/javascript">
	<!--
	if(DetectSmartphone() || DetectIpad() || DetectGameConsole()){
		//Action
	}
	//-->
</script>

-------------------------------------------------

3) JQuery simples


/*** sniff the UA of the client and show hidden div's for that device ***/
var customizeForDevice = function(){
    var ua = navigator.userAgent;
    var checker = {
      iphone: ua.match(/(iPhone|iPod|iPad)/),
      blackberry: ua.match(/BlackBerry/),
      android: ua.match(/Android/)
    };
    if (checker.android){
        $('.android-only').show();
    }
    else if (checker.iphone){
        $('.idevice-only').show();
    }
    else if (checker.blackberry){
        $('.berry-only').show();
    }
    else {
        $('.unknown-device').show();
    }
}

-------------------------------------------------

4) CSS at-rule

@media all and (max-width: 600px) { /* Largura do #screen */
	#elemento {}
}