Card clash: What is it, and how to avoid it

By Marianne Curphey

Recent issues have highlighted problems surrounding contactless technology and inspired Transport for London (TfL) to start publicity campaigns reminding travellers to keep their contactless cards separate.

Almost 1,800 commuters have received refunds after Oyster card readers, which take payment for buses and trains in London, picked up signals from other contactless cards in riders' wallets. The readers charged the wrong card, two separate cards or none at all, rejecting payment altogether. Such contactless payment reader mix-ups are called "card clash."card-clash

"If you touch your contactless payment card on a yellow card reader when it's in the same wallet or purse as another contactless card [such as an Oyster card or a pass to enter your workplace building], the reader might detect more than one card," says a TfL spokesperson.

The result: the card reader doesn't know which card to read. "If this happens on a bus, your fare could be charged to a card that you didn't intend to pay with," says the TfL spokesperson.

Alternatively, the yellow card reader could read one card when you touch it at the start of your journey and a different card at the end when you touch out, charging you twice.

Paul Makin, principal consultant for mobile money at Consult Hyperion -- which is TfL's technical adviser -- weighs in on consumer concerns about card clash.

Why is this happening?
When you present your wallet at the train or bus gates, the terminal sends out a general query and waits for a reply. The card sends back a signal and the terminal takes payment from it. But if you have more than one contactless card, the terminal may choose the one with the strongest signal.

"There is a priority order built into the terminal which means that TfL is set up to choose the Oyster card first," Makin explains. "However, it could be that the bank card sends the strongest signal instead, and the terminal hears that one and uses it to make the transaction."

"It is a technology issue -- people are not familiar with the technology, and the technology is rushing ahead," says Makin. "However, we are dealing with people, and the technology should adapt to them, rather than the other way round."

Is it just a problem on buses and trains?
No, there have been incidents in retail outlets as well, Makin explains.

"There have been scenarios were people wanted to pay in shops and they were resting their purse on the payment kiosk. The payment terminal took a payment from their contactless card, but neither they nor the retail assistant were aware this had happened," he says. "Then they paid for their goods with another card, and later found that they had been charged twice."

What can you do to prevent this happening?
Separate your cards into different parts of your wallet so that you tap the part of the wallet containing your Oyster card first. Or take the card out of your wallet and tap it on the terminal.

"It's always a good idea to take your contactless card out of your wallet to touch the reader -- this will make sure the right contactless card is debited. Payments can only take place where the card is placed within a few centimetres of the card reader," says a spokesperson from the UK Cards Association.

Alternatively, you can insulate the cards you don't want to use with aluminium foil, though the foil may also interfere with your Oyster card.

Makin says that as technology advances, card clash will be more preventable.

"When we move into a mobile world where we are all using mobile phones with Near Field Technology to make payments, you will have apps on your phone which will enable you to set the priority order of your cards. Plastic is less sophisticated," he says.

See related: How safe are contactless cards?, Contactless card payments now accepted on London buses

Published: 20 March 2014