# US 4,393,278 A · Telephone security system

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- Number: US 4,393,278 A
- Document ID: US4393278A
- Status: Granted
- Kind: A
- Application number: 06/181,993
- Filed: 1980-08-26
- Granted: 1983-07-12
- Earliest claimed: 1980-08-26
- Inventors: Allan M. Miyoshi
- Web page: https://patentgrep.com/patent/US4393278A

## CPC

- H04M 1/665: by checking the validity of a code
- H04M: TELEPHONIC COMMUNICATION (circuits for controlling other apparatus via a telephone cable and not involving telephone switching apparatus G08)

## Abstract

A unit is interposed between a telephone outlet and the set to answer a call and to respond to absence or presence of a subsequently dialed-in security code. Only when that code is dialed will the call be completed by effecting a through connection and causing the set to ring. This private unlisting automatically restricts accepting of calls only from callers to whom the code was given.

## Claims

### Claim 1

An apparatus interposed between a telephone subscriber outlet and a telephone, comprising:
input means including ring detector means connected to the outlet and including a first switch, the detector means responding to incoming ring signals and being connected for closing the switch, the first switch being included in a circuit which, when completed, provides a through-connection from the subscriber outlet to the telephone, the circuit and through-connection being, however, not yet completed when the first switch is closed, the circuit requires for completion that the first switch be closed as a preparation for such completion;
means connected to be responsive to the closing of the switch and being connected to the outlet upon closing of the switch to be effective across the outlet for establishing impedance conditions equivalent to answering a phone so that ring signals arriving at the outlet will stop;
signal-detecting means connected to the circuit as prepared by said first switch closing and being responsive to dial signals received through the outlet after closing of the first switch and after the ring signals have stopped;
logic circuit means connected to the signal-detecting means to determine agreement between a sequence of the dial signals representing a dialed-in number and a preset number;
output means including a ring generator and a second switch operated by the logic circuit means to complete a connection from said circuit as prepared by the first switch closing, to the ring generator and causing the ring generator to generate ringing signals for the telephone when said logic circuit has detected said agreement; and
means for completing the through-connection of the circuit as prepared, to extend between the outlet and the telephone following an actual answering of the telephone by a person.

### Claim 2 (depends on 1)

An apparatus as in claim 1, said means for completing including another detector means connected to the telephone and responding to a change in impedance conditions indicative of whether or not the telephone has been answered.

### Claim 3 (depends on 1, 2)

An apparatus as in claim 1 or 2, wherein the generation of ringing signals is separate from the telephone, the output means including a separate ring-back generator connected to the circuit and further connected to be activated by the logic circuit means, for providing ring-back signals into the outlet.