How to detect user coming from mobile device or desktop device?

The following module will help to identify the user agent with device:

Mobile Tools

Browsecap

The Browscap module provides a replacement for PHP's get_browser() function. get_browser() is difficult (or impossible) to configure for most users in shared webhosting situations, and requires attention to keep the underlying data (browscap.ini) up-to-date. This module avoids the configuration issue by storing the data in a database table, and the freshness issue by automatically retrieving the latest data on a weekly basis (if cron.php is run regularly).