助手类如下：
原理就是验证header头

<?php
/**
 * Created by PhpStorm.
 * User: QQ: 1716771371
 * oschina:http://git.oschina.net/zhaojunlike
 * github: http://github.com/zhaojunlike
 * Date: 2016/8/14
 * Time: 8:55
 */

namespace Common\Helper;


class MobileHelper
{


    static private $instance;


    public static function isMobile()
    {
        $_SERVER['ALL_HTTP'] = isset($_SERVER['ALL_HTTP']) ? $_SERVER['ALL_HTTP'] : '';
        $mobile_browser = '0';
        if (preg_match('/(up.browser|up.link|mmp|symbian|smartphone|midp|wap|phone|iphone|ipad|ipod|android|xoom)/i', strtolower($_SERVER['HTTP_USER_AGENT'])))
            $mobile_browser++;
        if ((isset($_SERVER['HTTP_ACCEPT'])) and (strpos(strtolower($_SERVER['HTTP_ACCEPT']), 'application/vnd.wap.xhtml+xml') !== false))
            $mobile_browser++;
        if (isset($_SERVER['HTTP_X_WAP_PROFILE']))
            $mobile_browser++;
        if (isset($_SERVER['HTTP_PROFILE']))
            $mobile_browser++;
        $mobile_ua = strtolower(substr($_SERVER['HTTP_USER_AGENT'], 0, 4));
        $mobile_agents = array(
            'w3c ', 'acs-', 'alav', 'alca', 'amoi', 'audi', 'avan', 'benq', 'bird', 'blac',
            'blaz', 'brew', 'cell', 'cldc', 'cmd-', 'dang', 'doco', 'eric', 'hipt', 'inno',
            'ipaq', 'java', 'jigs', 'kddi', 'keji', 'leno', 'lg-c', 'lg-d', 'lg-g', 'lge-',
            'maui', 'maxo', 'midp', 'mits', 'mmef', 'mobi', 'mot-', 'moto', 'mwbp', 'nec-',
            'newt', 'noki', 'oper', 'palm', 'pana', 'pant', 'phil', 'play', 'port', 'prox',
            'qwap', 'sage', 'sams', 'sany', 'sch-', 'sec-', 'send', 'seri', 'sgh-', 'shar',
            'sie-', 'siem', 'smal', 'smar', 'sony', 'sph-', 'symb', 't-mo', 'teli', 'tim-',
            'tosh', 'tsm-', 'upg1', 'upsi', 'vk-v', 'voda', 'wap-', 'wapa', 'wapi', 'wapp',
            'wapr', 'webc', 'winw', 'winw', 'xda', 'xda-'
        );
        if (in_array($mobile_ua, $mobile_agents))
            $mobile_browser++;
        if (strpos(strtolower($_SERVER['ALL_HTTP']), 'operamini') !== false)
            $mobile_browser++;
        // Pre-final check to reset everything if the user is on Windows
        if (strpos(strtolower($_SERVER['HTTP_USER_AGENT']), 'windows') !== false)
            $mobile_browser = 0;
        // But WP7 is also Windows, with a slightly different characteristic
        if (strpos(strtolower($_SERVER['HTTP_USER_AGENT']), 'windows phone') !== false)
            $mobile_browser++;
        if ($mobile_browser > 0)
            return true;
        else
            return false;
    }
}

Mobile_Detect是轻量级php库通过User-agent和特定的人Http头部来判断：

• Mobile_Detect

function is_mobile() {
    if(empty($_SERVER['HTTP_USER_AGENT']))return false;
    $user_agent = strtolower($_SERVER['HTTP_USER_AGENT']);
    $mobile_agents = Array("240x320","acer","acoon","acs-","abacho","ahong","airness","alcatel","amoi","android","anywhereyougo.com","applewebkit/525","applewebkit/532","asus","audio","au-mic","avantogo","becker","benq","bilbo","bird","blackberry","blazer","bleu","cdm-","compal","coolpad","danger","dbtel","dopod","elaine","eric","etouch","fly ","fly_","fly-","go.web","goodaccess","gradiente","grundig","haier","hedy","hitachi","htc","huawei","hutchison","inno","ipad","ipaq","ipod","jbrowser","kddi","kgt","kwc","lenovo","lg ","lg2","lg3","lg4","lg5","lg7","lg8","lg9","lg-","lge-","lge9","longcos","maemo","mercator","meridian","micromax","midp","mini","mitsu","mmm","mmp","mobi","mot-","moto","nec-","netfront","newgen","nexian","nf-browser","nintendo","nitro","nokia","nook","novarra","obigo","palm","panasonic","pantech","philips","phone","pg-","playstation","pocket","pt-","qc-","qtek","rover","sagem","sama","samu","sanyo","samsung","sch-","scooter","sec-","sendo","sgh-","sharp","siemens","sie-","softbank","sony","spice","sprint","spv","symbian","tablet","talkabout","tcl-","teleca","telit","tianyu","tim-","toshiba","tsm","up.browser","utec","utstar","verykool","virgin","vk-","voda","voxtel","vx","wap","wellco","wig browser","wii","windows ce","wireless","xda","xde","zte");
    $is_mobile = false;
    foreach ($mobile_agents as $device) {
        if (stristr($user_agent, $device)) {
            $is_mobile = true;
            break;
        }
    }
    return $is_mobile;
}

贴一下THINKcmf里面的代码

/**
 * 判断是否为手机访问
 * @return  boolean
 */
function sp_is_mobile() {
    static $sp_is_mobile;

    if ( isset($sp_is_mobile) )
        return $sp_is_mobile;

    if ( empty($_SERVER['HTTP_USER_AGENT']) ) {
        $sp_is_mobile = false;
    } elseif ( strpos($_SERVER['HTTP_USER_AGENT'], 'Mobile') !== false // many mobile devices (all iPhone, iPad, etc.)
            || strpos($_SERVER['HTTP_USER_AGENT'], 'Android') !== false
            || strpos($_SERVER['HTTP_USER_AGENT'], 'Silk/') !== false
            || strpos($_SERVER['HTTP_USER_AGENT'], 'Kindle') !== false
            || strpos($_SERVER['HTTP_USER_AGENT'], 'BlackBerry') !== false
            || strpos($_SERVER['HTTP_USER_AGENT'], 'Opera Mini') !== false
            || strpos($_SERVER['HTTP_USER_AGENT'], 'Opera Mobi') !== false ) {
        $sp_is_mobile = true;
    } else {
        $sp_is_mobile = false;
    }

    return $sp_is_mobile;
}

/**
 * 判断是否为微信访问
 * @return boolean
 */
function sp_is_weixin(){
    if (strpos($_SERVER['HTTP_USER_AGENT'], 'MicroMessenger') !== false) {
        return true;
    }
    return false;
}

当然，如果你还需要判断安卓或者ios的话，有一个简单的方法，移动端自定义HTTP_USER_AGENT的值，然后从服务端获取$_SERVER['HTTP_USER_AGENT']，例如，增加一个my_webapp,判断这个字符是否存在

$user_agent = $_SERVER['HTTP_USER_AGENT'];
            if (stripos($user_agent, 'my_webapp') !== false) {
                $this->assign("is_webapp", true);
        }

这个问题我在segment fault回答过，当时题主表示有效：/q/101...