A technique for improving the security of a portable consumer device may include storing a first account identifier and a second account identifier associated with the first account identifier, the second account identifier and the first account identifier being associated with the same account on the portable consumer device. When the portable consumer device is interacting with a reader device to conduct a transaction, the portable consumer device may determine whether the transaction is a proximity transaction by sensing whether a wireless interrogation signal is being transmitted from the reader device, and determine which of the first account identifier and the second account identifier to provide to the reader device based on whether the transaction is a proximity transaction.