> I've long been wanting RFID tags on everything sold so you could just
> pass the cart through a field, make your payment, and leave.  Never
> taking anything out of the cart, or your hands, etc.
>
>   

It's a nice idea and you can make it work well enough for a demo but in 
the real world it isn't practical.

Water and metal (cans/foil/metalised plastic packages) are all very bad 
for propogation of radio signals and are all found in substatial 
ammounts in random arrangements within a typical shopping trolly load. 
Theese are almost certain to block out some of the tags meaning those 
items won't be accounted for.
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