If you keep your Oyster card in your wallet or purse with your bank cards, you might occasionally see a red light when you touch it on a card reader at stations and on buses. The red light means you haven't paid for your journey and if you are at a ticket gate, it may not open. This can happen even if you've got enough pay as you go credit or a valid Travelcard on your Oyster card because you could be experiencing 'card clash'.
Many cards are now issued with contactless technology - the same as Oyster cards:
If you touch your Oyster card on a yellow card reader when it's in the same wallet or purse as another contactless card, the reader may detect more than one card. When this happens, the card reader doesn't know which one to read so rejects them and you could experience any of the following:
To avoid card clash:
Later in 2014, when contactless payment cards are accepted for travel on Tube, tram, DLR, London Overground and most National Rail services in London, one of the following could also happen:
Remember to separate your Oyster card from other contactless cards when touching in and out.