Smart card interfaces are devices used in smart card readers to transfer data between a processor system and a smart card. They are used in a variety of applications, for example set-top-boxes, bank teller card readers, pay TV, and for personal identification. There are both contactless and contact varieties. Any access to or from a smart card must be a secure transfer of data call a conditional access. There are a number of conditional access systems in use. An example of this is a common system called VideoGuard –a digital encryption system for use in digital satellite broadcasting. Access Ffags are downloaded by satellite or modem to a subscribers card that allow for rapid changes to the channel data, scrambling the signal unless the codes match the broadcast.

Smart card interfaces that make electrical contact with the smart card do so over a standard interface that is visible as a set of metallic contact pads on the card. The interface device provides power to the card electronics by this interface, as well as the serial data interface. The power supply is usually built into the smart card interface chip. The chip carries out at the appropriate time a sequence of serial communications called activation and deactivation sequences should a fault occur on the card or there is an error in the communications. The serial channel has a clock derived from an oscillator internal to the device. Smart card interfaces have good ESD protection -usually 6kV or more due to the physically exposed environment they may operate in. When used in a payment system, the hardware is designed to comply with the Europay, Mastercard and Visa (EMV) standard. Contact positions and transmission protocols, access methods to files are defined by the ISO 7861 standard, and for GSM cellphone Smart Cards, which is all covered in the GSM11.11 standard.

Contactless smart cards communicate to a terminal via radio waves. Contactless smart card readers are typically located close to a pin pad, fare box or other place associated with payment.  They interface in a similar way to RFID and require close proximity between card and reader. The standard that contactless smart card Interfaces must comply with is ISO/IEC 14443. Interfaces can at up to 100mm for some readers, but are typically much nearer than this. A contactless smart card interface must incorporate the ability to power the card via its inbuilt inductor using resonant inductive coupling.