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Passive remote access control system

  • US 6,570,486 B1
  • Filed: 04/09/1999
  • Issued: 05/27/2003
  • Est. Priority Date: 04/09/1999
  • Status: Expired due to Fees
First Claim
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1. A method for controlling access to a vehicle which has a door and an engine, that method comprising the steps of:

  • (a) periodically transmitting a first interrogation signal at a first rate from a control circuit on the vehicle;

    (b) receiving the first interrogation signal at a remote control that is separate from the vehicle;

    (c) upon receiving the first interrogation signal, transmitting a first reply signal from the remote control;

    (d) receiving the first reply signal at the control circuit;

    (e) after receiving the first reply signal, periodically transmitting a second interrogation signal at a second rate from the control circuit;

    (f) receiving the second interrogation signal at the remote control;

    (g) upon receiving each second interrogation signal, transmitting a second reply signal from the remote control;

    (h) receiving each second reply signal at the control circuit;

    (i) measuring strength of each second reply signal at the control circuit;

    (j) activating a first function of the vehicle when the strength exceeds a first predefined threshold; and

    (k) activating a second function of the vehicle when the strength exceeds a second predefined threshold.

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