Yagendoo Mobile Detection
The plug-in has a really simple design and helps users and developers find out, in their code, whether the device that the website is being visited on is a mobile device, such as a mobile phone or tablet PC, or not.
In addition, lots of other information, such as the operating system, user agent or exact type of mobile device, can also be checked and/or used.
Particularly in terms of "responsive web design", you will have some real tricks up your sleeve with the "Mobile Detection" - Joomla! Plugin – keen users and developers will know what we mean and know how to use it. ;-)
There is already a function in Joomla! that allows you to do this, but due to the complexity, Joomla! itself does not do this reliably enough, which is, of course, more or less the nature of the beast as the number of different mobile devices and operating systems is growing rapidly.