The simplest method is a JavaScript to identify the device.
Another option is search "mobile" within the user agent (browser ID).
Safari on iPad running iOS 5.1 is identified as
Mozilla/5.0 (iPad; CPU OS 5_1_1 like Mac OS X) AppleWebKit/534.46 (KHTML, like Gecko) Version/5.1 Mobile/9B206 Safari/7534.48.3
The script can be as simple as
jQuery(document).ready(function ($) {
var $is_mobile = false;
if (/Android|webOS|iPhone|iPad|iPod|BlackBerry/i.test(navigator.userAgent)) {
$is_mobile = true;
// you can redirect directly from this point
// use one of the methods only - uncomment the chosen method
// similar to HTTP redirect
// window.location.replace("http://your_mobile_friendly.com");
// similar to clicking on a link
// window.location.href = "http://your_mobile_friendly.com";
}
// keep processing the full landing page or do anything else if is_mobile = true
});