Bob van Vliet's frustration about the new Dutch public transport RFID card (OV Chipkaart) led to an appealing concept: equipping RFID cards with an e-paper displays so they can give status messages or warnings.

As it turns out, passive RFID can provide enough energy for a simple e-paper display. And that gives you all kinds of cool options. Displaying your credit of course, but the card could also display friendly messages like “have a good trip” while you’re checked in.

I could have used the 'have a good trip' message that indicates that you are checked in last week, when the PDA of the conductor was buggy and he kept telling me I had not checked in, while I kept insisting I did check in. When he rescanned by card for the fourth time his PDA yielded and my RFID card was victorious. "Oh, you did check in." Anyway, kudos to Bob for turning frustration into inspiration.