Of course, the simplest option is the addition of an RFID chip, the size of a grain of sand, which replicates the banknote serial number – so you can in theory count banknotes by scanning them with a suitable device as they move past. But that seems a little mundane.
Of far greater interest is the more complex idea of a smart banknote with a particular focus on their applications alongside mobile money in emerging markets. With the right combination of technologies, a smart banknote could be created whose appearance changed according to the value it currently represents; blank if it has no value, looking like a £10 note if it’s currently worth £10, etc.
It could then be integrated with your mobile phone and used to download money from your mobile money account (and change its face value accordingly) – and vice versa. Once it had value loaded, it could be used to buy things in shops just like ordinary notes.
Apart from the fact that this would reduce the need for ATMs and mobile money agents, it would also remove the huge costs associated with moving cash around – security guards, vans etc – the savings from which would allow blank smart banknotes to be issued for free (transporting them is cheap, because until you download cash onto them, they have no face value).
Of course, there’s always the crumple test standing in the way…