Contactless bank cards

Tony Naggs tony.naggs at
Wed Nov 17 01:49:27 GMT 2010

On 16 November 2010 10:37, Francis Davey <fjmd1a at> wrote:

> Actually my first worry on seeing these things advertised was
> something entirely legal. Along the lines of an unobtrusive sign
> saying "entrance fee £5" or something like that. Auto charge people as
> they walk in (does contactless have that range? Or will it) and then
> have plausible deniability for a criminal charge. Obviously some
> customers will complain and have a reasonable argument for restitution
> of the sum taken, but who cares.

Contactless credit cards are very similar to Oyster cards, and standard
readers have range of 2cm to 5cm or so. The radio power from the reader
is powering the chip in the card. Actually the electric field carries the
power, and as this follows an inverse square rule extending the range
significantly is hard (requiring lots of copper and current).

The Oyster card equivalents in Japan (Suica for local services in Tokyo)
are also used for small payments at booths and vending machines for
snacks & newspapers. This worked very well when I visited, and in the
nearly 10 years it has been operating I have not heard of any major
fraud incidents.

Possible defenses include keeping your credit cards in a screened tin
or wallet, or carrying detectors that light a warning LED when a field of
the appropriate frequency is detected.

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