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Physical presence digital authentication system

  • US 20040031856A1
  • Filed: 07/14/2003
  • Published: 02/19/2004
  • Est. Priority Date: 09/16/1998
  • Status: Active Grant
First Claim
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1. A one-way electronic card, comprising:

  • a card body that has a thickness less than 0.8 mm and a switch; and

    transmission electronics coupled to the switch that emit an ultrasonic acoustic signal when the switch is activated.

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