I did suggest a QR code but looked more into using the technology that the turnstiles use, NFC (Near Field Communication) technology, same as that used by the payment terminals so, the technology exists and is well proven. Apple initially restricted access to NFC for security but have opened it up to allow NFC tags to be read NDEF NFC Data Exchange Format types 1 to 5, I've no idea if the turnstiles are in this range. In theory City could introduce an app which could be used to access the ground. Lots of other advantages as well, fans forgetting their cards, people tend to have their phones with them at all times. Again as I suggested earlier a system could be implemented for all PL clubs so away tickets could be added to the app and then used to access the away grounds. NFC is available on most Android phones also