CA1301973C - Telephone call blocker - Google Patents
Telephone call blockerInfo
- Publication number
- CA1301973C CA1301973C CA000614819A CA614819A CA1301973C CA 1301973 C CA1301973 C CA 1301973C CA 000614819 A CA000614819 A CA 000614819A CA 614819 A CA614819 A CA 614819A CA 1301973 C CA1301973 C CA 1301973C
- Authority
- CA
- Canada
- Prior art keywords
- telephone
- call blocker
- telephone call
- connection
- blocker
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- 230000009977 dual effect Effects 0.000 abstract description 2
- 230000002093 peripheral effect Effects 0.000 description 5
- 238000012544 monitoring process Methods 0.000 description 4
- 238000012360 testing method Methods 0.000 description 4
- 238000010586 diagram Methods 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 241000700605 Viruses Species 0.000 description 1
- 239000000872 buffer Substances 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 238000013500 data storage Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000011017 operating method Methods 0.000 description 1
- 235000015277 pork Nutrition 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M1/00—Substation equipment, e.g. for use by subscribers
- H04M1/66—Substation equipment, e.g. for use by subscribers with means for preventing unauthorised or fraudulent calling
- H04M1/677—Preventing the dialling or sending of predetermined telephone numbers or selected types of telephone numbers, e.g. long distance numbers
Landscapes
- Engineering & Computer Science (AREA)
- Computer Security & Cryptography (AREA)
- Signal Processing (AREA)
- Telephone Function (AREA)
Abstract
ABSTRACT
A telephone call blocker is used to restrict calls to prohibited numbers by opening a relay and disconnecting the telephone line. The telephone disconnect device will operate with both pulse and dual tone multi-frequency telephone protocols and is separable being located between the telephone and the jack.
A telephone call blocker is used to restrict calls to prohibited numbers by opening a relay and disconnecting the telephone line. The telephone disconnect device will operate with both pulse and dual tone multi-frequency telephone protocols and is separable being located between the telephone and the jack.
Description
~3~t73 TELEPHONE CALL BLOCKER
INTRODUCTION
This invention relates to a telephone call 5 blocker and, more particularly, to a telephone call blocker used to disconnect the telephone line from a telephone which may be of either the pulse or dual tone multi-frequency protocolO
BACKG _ROUND~ OF~ THE INVENTION
It is often desirable, when a telephone is under the control of others, to restrict access of the telephone to the telephone line and, more specifically, to restrict the access of the user to certain telephone numbers. This reasons for this include cost, contamination and censorship. For example, computer viruses are rapidly spread over communication lines and it may be desirable to insulate a system for another. Similarly, the growth of the industry of "message lines" or "900" numbers may create large telephone bills to the telephone owner who would, i~` able, restriat the access of his telephone to CQrtain users.
Devices to restrict the use of telephones are, of course, well known. ~he first generation of such devices include a cylindrical lock which is physically located on a telephone and prevents the dial from being rotated. The second generation included devices internal to the telephone itself that electrically affected the placing of outgoing calls by means of switches or dials.
Such devices prohibited the dialling of individual digits such as the long distance prefixes "0" and "1" such as is disclosed in U. S. Patent 4,297,534, limiting the number of digits in a dialled number and limiting the time duration of a telephone call as is disclosed in U. S.
Patent 4,511,765. Such call restrictions were enforce by disconnecting the telephone from the line or by 3~ 3 intercepting the dialling signals before they reached the telephone line.
It is also known to use a microprocessor that can be instructed by a password user by a telephone pad to restrict calls such as is disclosed in U. S. Patent ~,2~7,534.
Such prior art devices have only provided support for DTMF or pulse dialling signals and not for both which is inconvenient. Likewise, the devices have been generally included within the telephone or its housing and such is undesirable to a user who has diferent expectations. Yet a further disadvantage is that such devices are reguired to be used with each telephone and are not operable to disconnect or restrict number access to extension telephones. Yet a further disadvantage is that the prior art devices are not able to restrict sequences of digits such as area code prefixes.
SUMMARY OF THE INVENTION
According to the invention, there is provided a telephone call blocker for connection between a telephone and an external telephone line, comprising first connection means for connection to the telephone and ; second connection means for connection to an external telephone line; means for interpreting a telephone number entered on said telephone to determine if it is a predetermined prohibited number; and means between the first and second connection means for disconnecting said telephone from the external telephone line responsive to ~.~., ~, , ` , .
.
~L3~ 3 2a said interpreting means determining that said telephone number is a prohibited number. The interpreting means may be programmed to determine if a long distance prefix i5 present in ~aid telephone number.
Also according to the invention, there is provided a telephone call blocker for connection to an external telephone line to block unauthorized calls made from a telephone connected to said telephone line, comprising first connection means for connection to the telephone and second connection means for connection to the external telephone line; means for interpreting a telephone number entered on said telephone to determine if it is a predetermined prohibited number; and means for sending a signal along the external telephone line to interfere with the signal generated by a prohibited number entered on the telephone, thereby preventing unauthorized use of the telephone.
An embodiment of the invention will now be described, by way of example only, with the use of drawings in which:
ib ~3~
Figure 1 is a block diagram of the hardware used in the telephone call blocker according to the invention;
Figure 2 is schematic diagram of the hardware illustrated in Figure l;
Figure 3 is a flowchart of the software routines used in the call blocker;
Figure 4 is the source code for certain of the software routines; and Figure 5 illustrates the port configurations according to the invention.
With re~erence now to the drawings, an overall view of the telephone call blocker, generally illustrated at 5 in Figure 1, is illustrated in block form. The blocker 5 comprises a microprocessor generally illustrated at 10, an EPROM generally illustrated at 30, an address bus generally illustrated at 20, a data bus generally illustrated at 21, an address decoder yenerally illustrated at 24, a DTMF detector generally illustrated at 70, a dial pulse detector generally illustrated at 60 and a line re.lay generally illustrated at 50.
Under control of a program stored in EPROM 30, the microprocessor 10 checks the DTMF detector 70 and the dial pulse detector 60 for incoming prohibited digits that would lead the relay 50 to open and thereby disconnect the telephone line at the line relay 50.
An overall schematic view of the circuit is seen in Figure 2. The heart o~ the circuit is the 6802 microprocessor 10 which contains a small amount of onboard nonvolatile RAM for data storage. EPROM 30 is connected ''`'` ' :
-~3C?~9'73 .
via the address bus 20 and the data bus 21 to the microprocessor 10. EPROM 30 permanently contains the preprogrammed software routines for running the system.
The data bus 21, 23, via line driver 22, feeds four peripherals through five I/O ports. The ports, to be described in greater detail hereafter, are "read only", "write only", and "read/write" as illustrated in Figure 5.
The address bus 20 connects the microprocessor 10 to decoders generally illustrated at 24, 25, respectively, which select among the ~ive(5) input/output ports using control lines 26.
The first peripheral is power light emitting diode ("LED") generally illustrated at 40 which indicates whether the unit is functioning properly. LED 40 is controlled by a write only port 41. Port 41 comprises latch 42 which is enabled by control line 43 to receive the state o~ one bit o~ the data bus 23 at 44.
The second peripheral is line relay 50 which is driven by SCR 51. Line relay 50 is used to connect and disconnect the telephone line at 56, 57. Line relay 50 is controlled by a write only port 52. The port 52 is comprised of a latch 53 enabled by control line 54 to receive the state o~ one bit o~ the data bus at 55.
The third peripheral is the dial pulse detector illustrated generally at 60. The dial pulse detector 60 comprises a comparator 61 and a counter 62. When a telephone number is dialled using the "dial pulse'~
protocol, the comparator 61 detects the number of electrical transitions or dial pulses on the line at 66 and the counter is incremented for each pulse. The value in counter 62 will then represent the telephone number puls~ dialled is read via the read only port illustrated generally at 63. When the pork is read, the value stored 3~
in the counter 62 is sent to data bus at 64 through four unidirecti~nal tri-state buffers generally illustrated at 65 as enabled by the control line 66.
The fourth peripheral is the DTMF detector illustrated generally at 70. The DTMF detector comprises DTMF decoder chip 71. The decoder chip 71 senses a DTMF
signal at 75, decodes it and stores the binary decoded version. This stored decoded version can be read via the read only port illustrated generally at 72. When the port is read, the value stored in the DTMF decoder chip 71 is sent to the data bus at 73 as enabled by the control line 74.
The fifth and final port, illustrated generally at 80, 90 is a read/write status and control port connected to the pulse counting circuitry 60 and the DTMF
decoding circuitry 70. Ports 80, 90 operate as follows.
Control lines 81, 91 ~nable the four unidirectional tri-state buf~ers 82, 83, 92, 93. Thus, one bit each of status data is received by the data bus 23 at 84 from the ~omparator 61 and at 94 from the DTMF decoder 71. At the same time, one bit each of control data from the data bus 23 is sent at 85 to the counter chip 62 and at 95 to the DTMF decoder 71.
OPERATION
In operation, reference is made to the main paths of the specific software flowchart or algorithm illustrated in Figure 3.
on power-up, the unit generally undergoes a self-test sequence. If the test is failed, the unit discomlects the phone line and gives an error signal. If the test is passed, the unit expressly cl~ars the security override that allows unrestricted dialling and then goes to a ready state.
`~ ~3~ 3 In the r~ady state, the unit monitors the telephone off-hook condition. If an off-hook signal is detected, the unit checks for dial pulse and DTMF signals, decoding them if they exist.
When the first digit is detected and decoded, it is subjected to two tests.
10Since the security override was cleared on start-up, the unit checks to see if the decoded digit is the beginning of the security code. If the digit is the beginning of the security code, the unit notes this information and monitors the line for further digits. If the security code is completely entered, the unit sets the security override.
If the first digit is not the beginning of the secuxity code, a check is performed to determine if the digit is a "0" or a "1" which would preface a long distance call. If it is, the unit briefly disconnects the phone line to disrupt the call. It displays an error condition and subsequently recommences the start-up routine.
If the first digit is not a "0" or a "1", then the unit stops monitoring digits until the receiver is placed back on the hook at which point the unit recommences the start-up routine.
If the security override has been set, the unit monitors the next digit to determine if the us~r wishes to change the security code.If the next digit is a "*" or a 'l2", the unit disconnects the phone line and commences the procedure to change the security code, finishing the procedure ~y recommencing the start-up routine.
~3~g'73 If the next digit is not a "*" or a "2", the unit stops monitoring the digits and allows the unrestricted use of the telephone until the receiver is placed back on the hook at which point the unit recommences the start up routine.
The selected portions of assembly code illustrated in Figure 4 provide further and enhance description of the routine.
Many modifications may be made in the apparatus and routines described which will still fall within the teachings of the invention. For example, although the flowchart illustratad in Figure 3 is specific in nature, many further operating methods for the flexible microprocessor based system could operate.
A further modification contemplates the unit monitoring sequences of numbers, such as long distance area code prefixes. Such monitoring could readily be accomplished according to tha invention by modifying the programming of the EPROM. For example, upon entering the unit's security override mode, the user would have the option of using the telephone's keypad to enter sequences of numbers to be restricted. These restrictions could be modified or bypassed from within the security override mode only. When the numbers were used outside of the security override mode, the unit would continue to monitor dialling after the first dialled digit, stopping only when it was satisfied that the number being dialled was not restricted.
Yet a further embodiment contemplated is the control of extension telephones. In this embodiment, the main unit would monitor the DTMF or dial pulse signals present on the telephone line and not just those originating from the nearest telephone. In response to the detection of any restricted number or numbers and as opposed to the previous embodiment which disconnected only the nearest telephone with the aid of a hardwired relay, th.is embodiment contemplates the master unit sending a special signal along the telephone line thereby preventing unauthorized use of each of the extension telephones.
Yet a further embodiment contemplates a battery backup for the telephone call blocker.
INTRODUCTION
This invention relates to a telephone call 5 blocker and, more particularly, to a telephone call blocker used to disconnect the telephone line from a telephone which may be of either the pulse or dual tone multi-frequency protocolO
BACKG _ROUND~ OF~ THE INVENTION
It is often desirable, when a telephone is under the control of others, to restrict access of the telephone to the telephone line and, more specifically, to restrict the access of the user to certain telephone numbers. This reasons for this include cost, contamination and censorship. For example, computer viruses are rapidly spread over communication lines and it may be desirable to insulate a system for another. Similarly, the growth of the industry of "message lines" or "900" numbers may create large telephone bills to the telephone owner who would, i~` able, restriat the access of his telephone to CQrtain users.
Devices to restrict the use of telephones are, of course, well known. ~he first generation of such devices include a cylindrical lock which is physically located on a telephone and prevents the dial from being rotated. The second generation included devices internal to the telephone itself that electrically affected the placing of outgoing calls by means of switches or dials.
Such devices prohibited the dialling of individual digits such as the long distance prefixes "0" and "1" such as is disclosed in U. S. Patent 4,297,534, limiting the number of digits in a dialled number and limiting the time duration of a telephone call as is disclosed in U. S.
Patent 4,511,765. Such call restrictions were enforce by disconnecting the telephone from the line or by 3~ 3 intercepting the dialling signals before they reached the telephone line.
It is also known to use a microprocessor that can be instructed by a password user by a telephone pad to restrict calls such as is disclosed in U. S. Patent ~,2~7,534.
Such prior art devices have only provided support for DTMF or pulse dialling signals and not for both which is inconvenient. Likewise, the devices have been generally included within the telephone or its housing and such is undesirable to a user who has diferent expectations. Yet a further disadvantage is that such devices are reguired to be used with each telephone and are not operable to disconnect or restrict number access to extension telephones. Yet a further disadvantage is that the prior art devices are not able to restrict sequences of digits such as area code prefixes.
SUMMARY OF THE INVENTION
According to the invention, there is provided a telephone call blocker for connection between a telephone and an external telephone line, comprising first connection means for connection to the telephone and ; second connection means for connection to an external telephone line; means for interpreting a telephone number entered on said telephone to determine if it is a predetermined prohibited number; and means between the first and second connection means for disconnecting said telephone from the external telephone line responsive to ~.~., ~, , ` , .
.
~L3~ 3 2a said interpreting means determining that said telephone number is a prohibited number. The interpreting means may be programmed to determine if a long distance prefix i5 present in ~aid telephone number.
Also according to the invention, there is provided a telephone call blocker for connection to an external telephone line to block unauthorized calls made from a telephone connected to said telephone line, comprising first connection means for connection to the telephone and second connection means for connection to the external telephone line; means for interpreting a telephone number entered on said telephone to determine if it is a predetermined prohibited number; and means for sending a signal along the external telephone line to interfere with the signal generated by a prohibited number entered on the telephone, thereby preventing unauthorized use of the telephone.
An embodiment of the invention will now be described, by way of example only, with the use of drawings in which:
ib ~3~
Figure 1 is a block diagram of the hardware used in the telephone call blocker according to the invention;
Figure 2 is schematic diagram of the hardware illustrated in Figure l;
Figure 3 is a flowchart of the software routines used in the call blocker;
Figure 4 is the source code for certain of the software routines; and Figure 5 illustrates the port configurations according to the invention.
With re~erence now to the drawings, an overall view of the telephone call blocker, generally illustrated at 5 in Figure 1, is illustrated in block form. The blocker 5 comprises a microprocessor generally illustrated at 10, an EPROM generally illustrated at 30, an address bus generally illustrated at 20, a data bus generally illustrated at 21, an address decoder yenerally illustrated at 24, a DTMF detector generally illustrated at 70, a dial pulse detector generally illustrated at 60 and a line re.lay generally illustrated at 50.
Under control of a program stored in EPROM 30, the microprocessor 10 checks the DTMF detector 70 and the dial pulse detector 60 for incoming prohibited digits that would lead the relay 50 to open and thereby disconnect the telephone line at the line relay 50.
An overall schematic view of the circuit is seen in Figure 2. The heart o~ the circuit is the 6802 microprocessor 10 which contains a small amount of onboard nonvolatile RAM for data storage. EPROM 30 is connected ''`'` ' :
-~3C?~9'73 .
via the address bus 20 and the data bus 21 to the microprocessor 10. EPROM 30 permanently contains the preprogrammed software routines for running the system.
The data bus 21, 23, via line driver 22, feeds four peripherals through five I/O ports. The ports, to be described in greater detail hereafter, are "read only", "write only", and "read/write" as illustrated in Figure 5.
The address bus 20 connects the microprocessor 10 to decoders generally illustrated at 24, 25, respectively, which select among the ~ive(5) input/output ports using control lines 26.
The first peripheral is power light emitting diode ("LED") generally illustrated at 40 which indicates whether the unit is functioning properly. LED 40 is controlled by a write only port 41. Port 41 comprises latch 42 which is enabled by control line 43 to receive the state o~ one bit o~ the data bus 23 at 44.
The second peripheral is line relay 50 which is driven by SCR 51. Line relay 50 is used to connect and disconnect the telephone line at 56, 57. Line relay 50 is controlled by a write only port 52. The port 52 is comprised of a latch 53 enabled by control line 54 to receive the state o~ one bit o~ the data bus at 55.
The third peripheral is the dial pulse detector illustrated generally at 60. The dial pulse detector 60 comprises a comparator 61 and a counter 62. When a telephone number is dialled using the "dial pulse'~
protocol, the comparator 61 detects the number of electrical transitions or dial pulses on the line at 66 and the counter is incremented for each pulse. The value in counter 62 will then represent the telephone number puls~ dialled is read via the read only port illustrated generally at 63. When the pork is read, the value stored 3~
in the counter 62 is sent to data bus at 64 through four unidirecti~nal tri-state buffers generally illustrated at 65 as enabled by the control line 66.
The fourth peripheral is the DTMF detector illustrated generally at 70. The DTMF detector comprises DTMF decoder chip 71. The decoder chip 71 senses a DTMF
signal at 75, decodes it and stores the binary decoded version. This stored decoded version can be read via the read only port illustrated generally at 72. When the port is read, the value stored in the DTMF decoder chip 71 is sent to the data bus at 73 as enabled by the control line 74.
The fifth and final port, illustrated generally at 80, 90 is a read/write status and control port connected to the pulse counting circuitry 60 and the DTMF
decoding circuitry 70. Ports 80, 90 operate as follows.
Control lines 81, 91 ~nable the four unidirectional tri-state buf~ers 82, 83, 92, 93. Thus, one bit each of status data is received by the data bus 23 at 84 from the ~omparator 61 and at 94 from the DTMF decoder 71. At the same time, one bit each of control data from the data bus 23 is sent at 85 to the counter chip 62 and at 95 to the DTMF decoder 71.
OPERATION
In operation, reference is made to the main paths of the specific software flowchart or algorithm illustrated in Figure 3.
on power-up, the unit generally undergoes a self-test sequence. If the test is failed, the unit discomlects the phone line and gives an error signal. If the test is passed, the unit expressly cl~ars the security override that allows unrestricted dialling and then goes to a ready state.
`~ ~3~ 3 In the r~ady state, the unit monitors the telephone off-hook condition. If an off-hook signal is detected, the unit checks for dial pulse and DTMF signals, decoding them if they exist.
When the first digit is detected and decoded, it is subjected to two tests.
10Since the security override was cleared on start-up, the unit checks to see if the decoded digit is the beginning of the security code. If the digit is the beginning of the security code, the unit notes this information and monitors the line for further digits. If the security code is completely entered, the unit sets the security override.
If the first digit is not the beginning of the secuxity code, a check is performed to determine if the digit is a "0" or a "1" which would preface a long distance call. If it is, the unit briefly disconnects the phone line to disrupt the call. It displays an error condition and subsequently recommences the start-up routine.
If the first digit is not a "0" or a "1", then the unit stops monitoring digits until the receiver is placed back on the hook at which point the unit recommences the start-up routine.
If the security override has been set, the unit monitors the next digit to determine if the us~r wishes to change the security code.If the next digit is a "*" or a 'l2", the unit disconnects the phone line and commences the procedure to change the security code, finishing the procedure ~y recommencing the start-up routine.
~3~g'73 If the next digit is not a "*" or a "2", the unit stops monitoring the digits and allows the unrestricted use of the telephone until the receiver is placed back on the hook at which point the unit recommences the start up routine.
The selected portions of assembly code illustrated in Figure 4 provide further and enhance description of the routine.
Many modifications may be made in the apparatus and routines described which will still fall within the teachings of the invention. For example, although the flowchart illustratad in Figure 3 is specific in nature, many further operating methods for the flexible microprocessor based system could operate.
A further modification contemplates the unit monitoring sequences of numbers, such as long distance area code prefixes. Such monitoring could readily be accomplished according to tha invention by modifying the programming of the EPROM. For example, upon entering the unit's security override mode, the user would have the option of using the telephone's keypad to enter sequences of numbers to be restricted. These restrictions could be modified or bypassed from within the security override mode only. When the numbers were used outside of the security override mode, the unit would continue to monitor dialling after the first dialled digit, stopping only when it was satisfied that the number being dialled was not restricted.
Yet a further embodiment contemplated is the control of extension telephones. In this embodiment, the main unit would monitor the DTMF or dial pulse signals present on the telephone line and not just those originating from the nearest telephone. In response to the detection of any restricted number or numbers and as opposed to the previous embodiment which disconnected only the nearest telephone with the aid of a hardwired relay, th.is embodiment contemplates the master unit sending a special signal along the telephone line thereby preventing unauthorized use of each of the extension telephones.
Yet a further embodiment contemplates a battery backup for the telephone call blocker.
Claims (18)
1. A telephone call blocker for connection between a telephone and an external telephone line, comprising:
first connection means for connection to the telephone and second connection means for connection to an external telephone line;
means for interpreting a telephone number entered on said telephone to determine if it is a predetermined prohibited number; and means between the first and second connection means for disconnecting said telephone from the external telephone line responsive to said interpreting means determining that said telephone number is a prohibited number.
first connection means for connection to the telephone and second connection means for connection to an external telephone line;
means for interpreting a telephone number entered on said telephone to determine if it is a predetermined prohibited number; and means between the first and second connection means for disconnecting said telephone from the external telephone line responsive to said interpreting means determining that said telephone number is a prohibited number.
2. A telephone call blocker as in claim 1, wherein said interpreting means is programmed to determine if a long distance prefix is present in said telephone number.
3. A telephone call blocker as in claim 2 and further comprising means for storing a security code and means for interrogating said telephone number to determine if said number is identical to said security code.
4. A telephone call blocker as in claim 1, 2 or 3, wherein said telephone is a pulse tone telephone.
5. A telephone call blocker as in claim 1, 2 or 3, wherein said telephone is a DTMF telephone.
6. A telephone call blocker as in claim 1, 2 or 3, wherein said telephone is a combination pulse tone and DTMF type telephone.
7. A telephone call blocker as in claim 1, 2 or 3 further comprising means for changing said security code.
8. A telephone call blocker as in claim 7 wherein said means for changing said security code is a keypad.
9. A telephone call blocker as in claim 7 wherein said means for changing said security code is a rotary dial.
10. A telephone call blocker for connection to an external telephone line to block unauthorized calls made from a telephone connected to said telephone line, comprising:
first connection means for connection to the telephone and second connection means for connection to the external telephone line;
means for interpreting a telephone number entered on said telephone to determine if it is a predetermined prohibited number; and means for sending a signal along the external telephone line to interfere with the signal generated by a prohibited number entered on the telephone, thereby preventing unauthorized use of the telephone.
first connection means for connection to the telephone and second connection means for connection to the external telephone line;
means for interpreting a telephone number entered on said telephone to determine if it is a predetermined prohibited number; and means for sending a signal along the external telephone line to interfere with the signal generated by a prohibited number entered on the telephone, thereby preventing unauthorized use of the telephone.
11. A telephone call blocker as in claim 10, wherein said interpreting means is programmed to determine if a long distance prefix is present in said telephone number.
12. A telephone call blocker as in claim 11, and further comprising means for storing a security code and means for interrogating said telephone number to determine if said number is identical to said security code.
13. A telephone call blocker as in claim 10 wherein said telephone is a pulse tone telephone.
14. A telephone call blocker as in claim 10, wherein said telephone is a DTMF telephone.
15. A telephone call blocker as in claim 10, wherein said telephone is a combination pulse tone and a DTMF type telephone.
16. A telephone call blocker as in claim 12, further comprising means for changing said security code.
17. A telephone call blocker as in claim 16, wherein said means for changing said security code is a keypad.
18. A telephone call blocker as in claim 16, wherein said means for changing said security code is a rotary dial.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000614819A CA1301973C (en) | 1989-09-29 | 1989-09-29 | Telephone call blocker |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000614819A CA1301973C (en) | 1989-09-29 | 1989-09-29 | Telephone call blocker |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1301973C true CA1301973C (en) | 1992-05-26 |
Family
ID=4140830
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000614819A Expired - Lifetime CA1301973C (en) | 1989-09-29 | 1989-09-29 | Telephone call blocker |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1301973C (en) |
-
1989
- 1989-09-29 CA CA000614819A patent/CA1301973C/en not_active Expired - Lifetime
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed |