[Roboprog]

Indeed. Google Wallet? As he described the scan-and-walk process, it sounds more like Google Shoplift -- but maybe that's just the first thing that came to my mind. Of course, if you had some kind of disposable "smart bag" to do an RFID scan of its contents, you might be getting somewhere with this.

[billybob]

I think that's overengineering. Why not just use weight, like they already do in the self-checkout line? Weigh the shopping cart full of groceries, subtract the weight of the cart itself, and compare to what they're paying for. If it seems wrong, investigate.