A system comprises: a payment accessory including: a payment accessory including: at least one payment data sensor, and an accessory housing defining a mounting interface carrying a set of electrical contacts; and an adapter including: an adapter housing defining (i) an accessory bay configured to removably receive the mounting interface of the payment accessory, and (ii) a device interface opposite the accessory bay, the device interface configured to couple the adapter to a mobile computing device to interconnect the electrical contacts of the mounting interface with the mobile computing device.