I think the explanation given in the link below should give you the answer.

7 Real Mobile Duplicate Content SEO Issues

Hope this helps

Whilst that link is informative it seems a little outdated despite its post date? It refers to WAP sites... that's really old school - i know because i used to build them! LOL

You can find current examples of what to do to prevent duplicate content issues direct from Googles Webmaster Guidelines.

Remember though that this is Google talking from a "Search Stand Point" and NOT a "Best Mobile User Experience Stand Point" there's a big difference!

For specific info about duplicate content look under the header - "Annotation in the HTML" on the following page:

https://developers.google.com/webmas...-sites/details

Hope that helps

Jay

Don't mess with a separate site for mobile.

Hire someone to create a mobile CSS file for your existing site, having a single site for desktop & mobile is a lot less confusion for you & your traffic.

Google the keyword responsive theme

A responsive web page changes the page layout (with CSS code) depending on whatever the traffic is viewing the web page with (desktop, cell, ipad, etc...).

What Yukon said and "no index" or "rel canonical" pages that are dups or very close.

Lets clear this up once and for all...

Responsive design
- Good for desktops and tablets
- Is a quick lazy fix for mobile since it hides, squeezes, and moves elements around to fit the visitors screen.
- Despite elements being hidden, and scaled they are still downloaded which impacts download speed and performance.
- The content is arranged in such a way typically pages are unnecessarily long and make the user scroll downwards continuously to find basic information
- Downside is that it cant be implemented on an existing site without some heavy customization
- File sizes are typically much larger and therefore put a burden on download speeds
- Scripts are not typically designed specifically for mobile which cause performance and compatibility issues
- The content is bloated and not designed for people looking for quick information or information on the go
- Mobile validation is usually poor to non existent which means you limit yourself to only a select number of mobile visitors
- Overall you get a ok to poor mobile experience
- Plus that everything is managed on the same site
- Is not specifically identified in google.com/m mobile search portal with a green handset
- Responsive templates are readily available, especially for Wordpress
- Typically responsive themes are simply bought templates and making changes to the actually design can be overwhelming and complicated for the basic user.
- A responsive design requires a lot more knowledge of HTML and CSS than someone designing a standalone mobile website.
- The time taken to create a responsive design you could have probably created twice as many mobile sites!
- Doesn't need special SEO implentation for Google to crawl and is recommended by Google.
- There is no duplicate content issues.

Mobile optimized websites
- Present mobile optimized content specifically for mobile devices...
- Uses smaller file sizes - means quicker downloads
- Uses mobile specific/compatible files - which means better performance
- Uses mobile optimized content so visitors can find the most important information quickly
- Offers options to view regular site (recommended if sites responsive) - best of both worlds
- Offers backwards compatibility for the broadest range of mobile devices, means it will work on non smartphones too...
- Offers overall the best mobile user experience
- Excellent mobile validation scores and load load speed scores
- Is specifically identified with a green handset icon in Google.com/m mobile search portal when designed properly
- Downside is the content is typically separate from the main site
- Another downside is the time it takes to setup - however it can be sped up with the use of design tools and experience.
- Making simple changes doesn't have a snowball impact on the main site and is typically very easy to do.
- Mobile sites are very basic and therefore very easy to create.
- Mobile web site generators are typically limited in functionality and white label can be costly
- Mobile web site generator plugins for CMS's for Wordpress are far and few between and typically don't fully address mobile validation and load page speed.
- Requires additional action to make it SEO friendly for Googles search bots.
- There can be duplicate content issues if not addressed properly.

Adaptive mobile optimized web sites
- Has the same positives as a standalone mobile site
- Has the same positives as a responsive design
- The only downside is the learning curve and technical know how to implement something like this
- Can be self hosted
- Very few good ones currently available for Wordpress, Joomla, etc - WPTouch offers an optimized approach but lacks many features out of the box.
- Requires less implementation than mobile optimized websites to be search friendly by Google
- There is no to little duplicate content again depending if you address it properly.



Take a look at the top 250 corporate websites in Alexa and you will find that almost all of them have a mobile presence of which 98% of them are running a standalone mobile optimized site or a an adaptive mobile optimized website hardly any are using responsive design... why? they know and understand the importance of offering the best mobile user experience....

Responsive is great for desktops and tablets - but you can't beat a mobile optimized website when it comes to offering the best end mobile user experience to the broadest range of mobile users...

Our approach for new sites is to use a responsive design to accommodate desktop and tablet users but we implement our own adaptive design approach to provide a mobile optimized content to our mobile visitors... to us that's a winning combination

End of the day use what you think is best but be aware of all the pros and cons - responsive offers mobile readiness but is far from being mobile optimized and that seems to be the biggest misconception people have about responsive design.

I am interested to see other peoples pros and cons on this.


Hope this helps,

Cheers,

Jay

@John and OP - I would still follow Googles guidelines and implement what they recommend for standalone mobile sites ie Google mobile site map, canonical urls, etc

Whilst Google recommends responsive design from a search point of view so they can more easily search your content, just like they can any other desktop website (because that's what it is, basically a desktop website designed to fit any screen size). Yes in the same sentence they also accept that mobile sites and adaptive sites that deliver content dynamically on the same URL are also acceptable practices that will also get crawled. However from a user experience the Google Mobile initiatives clearly identifies that they recommend specific mobile optimized content from a mobile user standpoint.

For adaptive design you will need to add Vary PHP headers plus a mobile Google site map also isn't a bad idea

For responsive there are zero triggers to tell Google that site is designed for mobile - it will just consider it another desktop website

Google has made it quite clear that page speed is of importance when it comes to SEO - so makes sense that a mobile site MUST also be fast.

Thankfully for now the Google search portal for smartphones lumps all mobile and desktop sites into the same pool and doesn't differentiate with any form of identification which is specifically a desktop site or a mobile site - which is different from how Googles mobile search portal for non smartphones work.... ie it identifies mobile websites with a green handset icon

Should Google change or choose to identify mobile websites in the smartphone search portal there will be a lot of disappointed people with responsive designs that wont get identified.

They recently added more mobile search bots to their existing non smartphone mobile search bots - and along with the GoMo initiative its obvious they are very aware of the growing mobile scene.

You will find that using Googles Smartphone portal that sites that have a mobile site will get directly linked to and will have the desktop site completely bypassed.

Hope that helps

Jay

Hey guys (Jay and Yukon), you are confounding me with various types of mobile designs. I just asked whether having a separate mobile website (which is a sub-domain of my main domain) will trigger duplicate content issues ?
Please don't be antipathetic to one another. I respect your great amount of knowledge regarding various types of mobile designs, but that's not something i asked in the very first place. I just asked about

I thought you could just have one site with if statements to separate mobile and computer. i.e different css sheet and layout.

actually never though of this but how would google see that? Do they only take into account the computer version?

It will be a new site dude. So I think you can be in problem. So avoiding it is better.

Thanks to everyone for replying to my query, especially Yukon and Jay.
@ Yukon: i liked your idea of having just one website with a responsive theme. There is no need for redirection and link popularity/SEO remains intact. But can you tell me how can i do this for a blogger template? I am not at all into designing and coding related stuff.

@Jay: Your Google developers' link helped me a lot. Thank You.