A thin-client access card has a card body with partial or fully emissive magnetic data tracks. An emissive element is disposed in the card body under the location of the legacy magnetic data tracks. An electronic signal conditioner converts audio signals from a mobile device into magnetic data applied to the emissive element. A swipe sensor detects when the thin-client access card is being swiped by a legacy card reader, and triggers an output of magnetic data from the emissive element while proximal to the POS reader head. A cable attaches the thin-client access card as a peripheral to the mobile device with an audio output jack.