Dave Liquorice wrote:

RFID, I wonder. Have to be pretty short range and directional for it
to be 100% sure that a given product response is from a product in a
given trolly not in the next checkout or on the rack next to the
checkout.

I believe that this is an area IBM is actively working on[1]. As I
understand it, a big part of the difficulty is with responses
interfering with each other when you excite a whole basket's worth of
tags at once. That and shiny foil crisp packets.

And how about shopping from a another store that you have
with you that is also stocked in this store?

This is really just a subset of the "detecting items after you've bought
them" problem. Not surprisingly, people (myself included) don't like the
idea that a scanner could be pointed at them in the street and report on
every item in their possession[2]. It doesn't take too big a tabloid
leap to characterise this as remote secret frisking. So there's clearly
a need for "one-shot" tags that are neutralised when the goods are sold.
These exist at present in the form of tags with their aerials in
perforated "wings" that get snapped off at the checkout, but that
doesn't really work for the "walk through an arch and get billed for
what you're carrying" model. Presumably you could fry the chips with a
strong enough transmission, but that's going to either (a) fry the
customers too or (b) be harmless to the customers but cause no end of PR
damage as they *think* they're being fried.

Pete

[1] I should point out that *I'm* not working on it, and have no special
insight in this area.
[2] If it's the kind of item that today would carry a barcode,
obviously. But that covers pretty much anything you buy in a shop.