The Octopus card uses radio frequency identification (RFID) technology so that users need only hold the card in front of the reader. Physical contact is not required, and the card need not even be taken out because the reader can penetrate through material. This fare collection system has been so popular that many cities such as Singapore, London, Chicago, and Taipei have adopted the idea, launching their own version of smart cards, respectively named EZ-link, Oyster card, and EasyCard.