A mobile communications device is described which includes an input sensor, a memory unit, processing unit, and an antenna configured to wirelessly transmit and receive financial account data for a transaction. The antenna is configured to receive a request for data stored on the memory unit, and may also be configured to induce a voltage from a magnetic field to power certain components of the device. The input sensor may control whether the components can be so powered from the magnetic field. Alternatively, input from the input sensor may otherwise control the functionality of the device. By way of example, data representative of an input received by the input sensor may be transmitted in addition to the requested data.