Detect User Agent

index.php

<?php

include_once('functions.php');
if(isfrommobile()){
echo 'The user is from mobile'; 
}else {
echo 'The user is from PC'; 
}
?>

functions.php

<?php

function isfrommobile($useragent='') {
$useragent=(empty($useragent))?$_SERVER['HTTP_USER_AGENT']:$useragent;
if (preg_match(

'/android|avantgo|blackberry|blazer|compal|elaine|fennec|hiptop|
iemobile|ip(hone|od)|iris|kindle|lge |maemo|midp|mmp|opera m(ob|in)i|palm( os)?|
phone|p(ixi|re)\/|plucker|pocket|psp|symbian|treo|up\.(browser|
link)|vodafone|wap|windows (ce|phone)|xda|xiino/i', 
$useragent) || preg_match('/1207|6310|6590|3gso|4thp|50[1-6]i|770s|
802s|a wa|abac|ac(er|oo|s\-)|ai(ko|rn)|al(av|ca|co)|amoi|an(ex|ny|yw)|
aptu|ar(ch|go)|as(te|us)|ttw|au(di|\-m|r |s )|avan|be(ck|
ll|nq)|bi(lb|rd)|bl(ac|az)|br(e|v)w|bumb|bw\-(n|u)|
c55\/|capi|ccwa|cdm\-|cell|chtm|cldc|cmd\-|co(mp|nd)|craw|
da(it|ll|ng)|dbte|dc\-s|
devi|dica|dmob|do(c|p)o|ds(12|\-d)|el(49|ai)|em(l2|ul)|er(ic|k0)|
esl8|ez([4-7]0|os|wa|ze)|
fetc|fly(\-|_)|g1 u|g560|gene|gf\-5|g\-mo|go(\.w|od)|
gr(ad|un)|haie|hcit|hd\-(m|p|t)|hei\-|
hi(pt|ta)|hp( i|ip)|hs\-c|ht(c(\-| |_|a|g|p|s|t)|tp)|hu(aw|tc)|
i\-(20|go|ma)|i230|iac( |\-|\/)|ibro|idea|ig01|ikom|im1k|inno|
ipaq|iris|ja(t|v)a|jbro|jemu|jigs|
kddi|keji|kgt( |\/)|klon|kpt |kwc\-|kyo(c|k)|le(no|xi)|
lg( g|\/(k|l|u)|50|54|e\-|e\/|\-[a-w])|libw|lynx|m1\-w|m3ga|m50\/|
ma(te|ui|xo)|mc(01|21|ca)|m\-cr|me(di|rc|ri)|mi(o8|oa|ts)|mmef|
mo(01|02|bi|de|do|t(\-| |o|v)|zz)|mt(50|p1|v )|mwbp|mywa|
n10[0-2]|n20[2-3]|n30(0|2)|n50(0|2|5)|n7(0(0|1)|
10)|ne((c|m)\-|on|tf|wf|wg|wt)|nok(6|i)|nzph|o2im|op(ti|wv)|oran|owg1|
p800|pan(a|d|t)|pdxg|pg(13|\-([1-8]|c))|phil|pire|pl(ay|uc)|
pn\-2|po(ck|rt|se)|prox|psio|pt\-g|qa\-a|qc(07|12|21|32|60|
\-[2-7]|i\-)|qtek|r380|r600|raks|rim9|ro(ve|zo)|s55\/|sa(ge|ma|mm|ms|ny|
va)|sc(01|h\-|oo|p\-)|sdk\/|se(c(\-|0|1)|47|mc|nd|ri)|sgh\-|
shar|sie(\-|m)|sk\-0|sl(45|id)|sm(al|ar|
b3|it|t5)|so(ft|ny)|sp(01|h\-|v\-|v )|sy(01|
mb)|t2(18|50)|t6(00|10|18)|ta(gt|lk)|tcl\-|tdg\-|tel(i|m)|
tim\-|t\-mo|to(pl|sh)|ts(70|m\-|m3|m5)|tx\-9|up(\.b|g1|si)|
utst|v400|v750|veri|vi(rg|te)|vk(40|5[0-3]|\-v)|vm40|voda|
vulc|vx(52|53|60|61|70|80|81|83|85|98)|w3c(\-| )|
webc|whit|wi(g |nc|nw)|wmlb|wonu|x700|xda(\-|2|g)|yas\-|
your|zeto|zte\-/i', substr($useragent, 0, 4)))
                return true;
            else
                return false;
        }
?>

Sample Code