It is possible to connect an external door reader to an entrance; the external reader would typically be connected outside the library and control only the outer door, after which the main entrance unit is installed, controlling the actual door to the library.

The external reader does not have a screen or a pin pad, only barcode - and optionally RFID/Mifare - reader. It does not validate patron PIN code, only that the patron exists and is valid for entry. Once the patron has been granted access from the external reader, a new validation needs to be done in the actual entrance unit with PIN code verification.

The external reader can control separate IO channels, to open a different door than the main entrance unit would open.