US PATENT SUBCLASS 340 / 296
.~.~.~ Key obstruction type

Current as of: June, 1999
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340 /   HD   COMMUNICATIONS: ELECTRICAL

286.01  DF  SYSTEMS {24}
287  DF  .~ Signal box type (e.g., to call messenger, plural fire alarm boxes) {11}
295  DF  .~.~ Noninterfering (prevents break-in by another box during transmission) {1}
296.~.~.~ Key obstruction type

DEFINITION

Classification: 340/296

(under subclass 295) Subject matter provided with means to obstruct the entrance of the key which is used to operate the signal box, said means operating to prevent insertion of the key only during the transmission of a signal sequence.