Smart shopping - the retail trend of Christmas 2012 - what you should know.
Once your Smartphone app reads the product barcode (often called a QR Code) you have all you need to find the best deals.
This booming trend of Christmas 2012 is called "showrooming" ...because it risks leaving some stores as unwilling showrooms for products people will actually buy cheaper elsewhere.
Search the app stores and you will find plenty of them that help compare prices this way - give them a go, its all free.
I spoke to Philip Beeching (who runs a great internet marketing blog) who told me how he took "showrooming" to extremes when he went to a shop, smelled the perfume - got advice from the specialist staff - then saved £50 by buying online.
New industry figures we got today show 28% of people use smartphones to compare prices whilst in a shop.
That's around 10% higher than a year ago. After comparing, 9% then went on to buy elsewhere.
In High Street stores, 47% of shoppers now use their smartphones.
Rob Skinner of Paypal told me its "a retail revolution".
Many shops are fighting back.
I went to HMV who are improving their own internet offering - and who warn that if showrooming continues to gather momentum it could threaten the survival of some specialist stores.
The unstoppable force of the phone that's changed so much - is now reshaping shopping.
As the phenomenon called "showrooming" leaves stores not only there for the convenience of their customers - but also grudgingly benefiting their online rivals too.