Ping Pong Gates
Patent number: 200902Imagine you are blind. Life is pretty difficult then. But sometimes things are made even more difficult. For example at the entrance gates to train or metro. These gates play a beep when you hold your chip card at the gate. For the seeing, there is a small screen that shows your last transaction too. The blind just hear tens of beeps, not knowing whether it is yours or your neighbour's.
That's why the blind get a "pong" card. Among all the people who hear "ping"you will hear "pong". That way you know your blind transaction succeeded.
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