Bell Telephone Laboratories

American Telephone and Telegraph Company, At&t Technologies, Inc.

Arden Bernard Wright

Alan M Gordon

Ronald E Anglikowski

Edward Francis Mazurek

Nissin Habib

A security system for cordless telephones prevents unauthorized telephone lls over telephone lines. The system includes a base unit and a cordless handset unit which must share common information for proper operation. To prevent an unauthorized user in possession of a handset unit from easily matching a security code stored in the base unit and thereby obtain dial tone therefrom, the security code in the base unit is transferred to the handset unit while the handset unit is in a mating cradle in the base unit. Transfer circuits in the base unit and the handset unit respectively transmit and receive the security code and also an operating frequency channel over a direct-current charging path provided for charging of a battery in the handset unit whenever the handset unit is returned to the cradle.

Security arrangement for cordless telephone system

Telephone terminal equipments connected to the network through the device described herein are prevented from applying potentially human-hazardous voltages or currents to the network. The device includes a pair of bifilar relay coils, one in each connection to the central office. These operate an associated relay contact only when an unbalanced voltage or current condition occurs on the customer leads. A circuit path is thus completed to operate a second relay, which opens the connection between the customer terminal leads and the network leads; and establishes a path to ground through its own coils for the current from the unbalanced source. Means are included for assuring that the fraction of hazardous voltage appearing across the second relay remains essentially constant in the frequency range of 17 to 60 hertz. Only removal of the unbalanced current can release the relay and restore the network connection.

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Freehold, NJ, United States of America

Arden Bernard Wright