Methods, systems, and apparatus, including computer programs encoded on computer storage media, for modulating card information between a card reader and a user device. One of the methods includes receiving, from a read head of the card reader, card information associated with a card. The card information is encoded in a first format to be sent to the user device at a first data rate. The card information is encoded in a second format to be sent to the user device at a second data rate lower than the first data rate. The card information is sent to the user device encoded in the first format and the second format.