Contactless bank cards

[Roland Perry]

In article <20101116163933.GL535 at snowy.squish.net>, Jon Ribbens 
<jon+ukcrypto at unequivocal.co.uk> writes
>> In most shops my observation (from the customer side of the till) is
>> that to "put through" a card transaction you first need to ring up a
>> sale on the till, and then link that transaction to the C&P terminal.
>> You can't just "invent" a transaction out of thin air (the way you used
>> to be able to with carbon paper receipts and the mechanical swipe
>> machines).
>
>Oh, well in small retailers my observation, and also as I understand
>it, reality, is that the merchant terminal is usually not connected to
>the till and you can put any number of transactions through without
>the till knowing anything about it.

As the terminal isn't touched by the merchant (unless it's a cordless 
one) how do they instruct it to initiate a transaction.

Meanwhile, is there any such thing as a cordless (handheld, like in a 
restaurant) paywave terminal?
-- 
Roland Perry