A financial transaction card reader device , comprising: a housing having a slot for swiping a magnetic stripe of a financial transaction card to complete a financial transaction between a buyer and seller; a read head in the housing for reading data stored on the magnetic stripe and for producing a signal indicative of data stored on the magnetic stripe; an output jack adapted to be inserted into a microphone input associated with a mobile device ; and passive ID circuitry in the housing of the financial transaction card reader device configured to deliver a unique ID of the financial transaction card reader device to the mobile device, wherein the passive ID circuitry further comprises: a unique ID storage comprising memory for containing the unique ID; a power subsystem , for providing power to enable communication with the mobile device ; a pathway subsystem for routing signals to the output jack ; a communication subsystem for reading and transmitting the unique ID from the unique ID storage ; and a control unit for configuring the pathway subsystem to allow the communication subsystem to transmit the unique ID via the output jack to the mobile device and then for configuring the pathway subsystem to allow the read head to provide the signal indicative of data stored on the magnetic stripe to the mobile device via the output jack . a housing having a slot for swiping a magnetic stripe of a financial transaction card to complete a financial transaction between a buyer and seller; a read head in the housing for reading data stored on the magnetic stripe and for producing a signal indicative of data stored on the magnetic stripe; an output jack adapted to be inserted into a microphone input associated with a mobile device ; and passive ID circuitry in the housing of the financial transaction card reader device configured to deliver a unique ID of the financial transaction card reader device to the mobile device, wherein the passive ID circuitry further comprises: a unique ID storage comprising memory for containing the unique ID; a power subsystem , for providing power to enable communication with the mobile device ; a pathway subsystem for routing signals to the output jack ; a communication subsystem for reading and transmitting the unique ID from the unique ID storage ; and a control unit for configuring the pathway subsystem to allow the communication subsystem to transmit the unique ID via the output jack to the mobile device and then for configuring the pathway subsystem to allow the read head to provide the signal indicative of data stored on the magnetic stripe to the mobile device via the output jack . a unique ID storage comprising memory for containing the unique ID; a power subsystem , for providing power to enable communication with the mobile device ; a pathway subsystem for routing signals to the output jack ; a communication subsystem for reading and transmitting the unique ID from the unique ID storage ; and a control unit for configuring the pathway subsystem to allow the communication subsystem to transmit the unique ID via the output jack to the mobile device and then for configuring the pathway subsystem to allow the read head to provide the signal indicative of data stored on the magnetic stripe to the mobile device via the output jack . <EOS>