Google has revolutionised web advertising with its AdSense system, which displays adverts for products related to the page being viewed. Now it wants to do the same for billboard ads.

In a patent the company has filed, it argues that however glitzy the ads that run on electronic billboards in shopping malls and out on the street, they are all but useless if local stores have not got the advertised products in stock. Google has come up with a system that only advertises products available nearby.

Stores buying advertising time on local electronic billboards are able to connect their stock-control computers to the network. The ads are displayed in rotation, but only until the stock-control computer reports the product as sold out. At that point, the ad is omitted from the cycle until the product is restocked.