How to check if user is using mobile device in Drupal or PHP

Following regex can be used to determine if the user is using mobile or not.

echo preg_match("/(android|avantgo|blackberry|bolt|boost|cricket|docomo|fone|hiptop|mini|mobi|palm|phone|pie|tablet|up\.browser|up\.link|webos|wos)/i", $_SERVER["HTTP_USER_AGENT"]);

Global array  $_SERVER["HTTP_USER_AGENT"] can also be printed to get user information.