Redirecting them isn't really a great idea. You end up frustrating more people than it's worth. The better option is a banner that displays at the top of the page. Here's how I've done it in the past for clients:

<body>

<div id="my-app-banner">yada yada yada</div>
</body>

css:

#my-app-banner {
display:none;
position:absolute;
top:0;
left:0;
width:100%;
(whatever else you want)
}

.show-app-banner {
    padding-top: {same height as your banner}
}

.show-app-banner #my-app-banner {
display:block;
}

Javascript:

if (navigator.userAgent.match(/Android|iPhone|iPad|iPod/i)) {
    $('body').addClass('show-app-banner');
}


Depending on your theme you will have to play with the css. Best thing about this approach is you can easily do it in a module or the theme and even exclude pages by path. And since this is targetting smartphones with support for modern CSS, you can really design something nice in pure CSS (gradients, shadows, border radius, etc.), plus use CSS3 transitions to animate things.

Also adding a close button is considered very friendly.
Jamie Holly
http://hollyit.net
On 3/11/2014 7:09 PM, Néstor wrote:
I need information on how to detect mobile devices on our desktop site and
once detected then display a splash or page or redirect the user to a page


The page or splash will have information that will ask the user to either continue to
the desktop site or to go to the "APP store"  (android, Iphone).  I will also set a cookie
so the user does not get this page/splas over and over.

Now, I managed to add some code on my page.tpl.ph that check the HTTP_USER_AGENT
it will set a cookie and then it will redirect them to another page (mobileandoir or mobileiphone)

This is working fine but I was wondering if there are site out there done in Drupal that have
a similar system set in place.

Can anyone provide information about this and how other people have done it..

I am using Drupal 6

Thanks,

Rotsen