WO1987007800A1 - Telephone security system - Google Patents

Abstract

To prevent unauthorized use of a telephone, a 4-digit access code must be dialled before the desired number. The dialled access code digits are detected (at 21, 22, 23) and each digit in turn is compared (at 26) with a corresponding stored access code digit from memory (25). A line reset relay (13) is opened on each such digit, so signalling a dialling abort and hang-up to the exchange. If the dialled and stored access codes match, flip-flop (35) remains set, and after the 4th digit gate (36) inhibits further comparisons, so the desired number can then be dialled. Otherwise, the operation repeats, with the system again monitoring for the access code. Means also allowing calls to emergency and a single programmable number can be provided. The system can also provide logging of calls from a private exchange, and control of calls depending on time, whether the call is long-distance or international, etc.

Description

Telephone Security System

The present invention relates to telephone security systems; that is, to means which prevent the unauthorized use αf a telephone. The invention also relates tα telephone monitoring systems; that is, to means which monitor and manage the use of a telephone.

The mechanical barrel lack is a well-known type αf telephone security system. This lock is a device which can be fitted and locked into any selected fingerhole of a rotary telephone dial. It therefore mechanically prevents any higher digit than that αf the hole it is fitted into from being dialled, since it cannot be moved past the finger stop. It can be fitted in the 1 hale, thus preventing any use of the telephone, or in the 9 hole, thus allowing 999 calls but preventing any calls tα numbers which include a 0.

Some elaborate private exchanges incorporate electronic security systems, which can be set tα prevent calls tα specified numbers of classes of numbers.

The mechanical barrel lock is simple, but somewhat limited, and it cannot be readily adapted far use with modern digital (keypad or tone signal) telephones, The private exchange security systems are limited to private exchanges and are obviously out αf the question for individual telephones.

There is thus a need far an improved telephone security system which can be used with individual telephones and can be used with digital telephones.

For domestic users, a security system is often all that is required, but many businesses, bath large and small, not only need a security system but also have a need to monitor telephone calls. Such^" monitoring must produce a record of what calls have been made. This facility is provided by the more elaborate types of private exchanges. However, there is no system available which provides this facility, in combination with a security system, with a cost αf the order αf £100 tα £1000 instead of the cost of private exchanges with such facilities (which cost typically from around £5000 upwards⁾.

Accordingly the present invention provides a telephone monitoring system characterized by detection means for detecting, on a telephone line, a code sequence dialled from a telephone, and an interrupter fitted in the telephone line and operable under the control αf the detection means when the code sequence has finished.

The monitoring system thus requires a code sequence to be dialled from the telephone being monitored, followed by the desired number; the system detects the code sequence and operates the interrupter between the code sequence and the fallowing desired number. The public exchange tα which the telephone line is connected thus sees the code sequence followed by a termination signal which aborts the effect of the code sequence and resets the line. This is followed by the desired number, which the public system thus responds tα as the start of a new call and so connects correctly.

The invention further provides a telephone security system comprising such a monitoring system, characterized by comparison means, associated with the detection means, operable to repeatedly operate the interrupter if the . dialled code sequence does not match a stored cade sequence.

The security system thus checks whether the correct code sequence has been dialled, and if it has not, it repeatedly operates the interrupter if the user then attempts tα dial a desired number, causing the public exchange to see repeated aborts of the dialling and so preventing the user from obtaining the desired number.

The system has no effect on incoming calls, and can readily be designed tα operate with either pulse or tone dialling.

The invention finds its major practical applications in two different fields, domestic and business, and takes somewhat different forms in these two fields. In the domestic field, the inventio - is preferably embodied as a small unit, which may be attached to or incorporated in a junction bαx, and is powered from the telephone line itself . It will provide protection against unauthorized calls from any telephone on the far side of the installation from the exchange. It may be designed so that it also detects and prevents calls from telephones on the exchange side αf the installation.

The unit may be made programmable, with a separate control unit which can be plugged into it tα program it. Thus the code sequence - the access code - can be changed at will, on a regular basis if desired, or set tα a value easily remembered by the user. The control unit preferably retains the access code, with the unit accepting instructions from the control unit only if the access codes in the unit and the control unit match, to prevent reprαgramming by another unit.

In the business field, the invention is preferably embodied as a control unit which is installed on the public utility side of a private branch exchange, and is connected to a host computer system (which may conveniently be a micro¬ computer). The system then operates as a sophisticated call logging and analysis system, in addition to performing the basic security functions. These functions may be considerably more elaborate than in a domestic system. Thus control αf calls by time of day (inside or outside working hours), with barring αf certain types αf call (such as long distance or international calls) may be provided.

Both farms of the invention, domestic and business, are preferably arranged so that certain numbers - the emergency number (999) and one or more preset or preferably programmable numbers, - may be dialled without inter¬ ference from the system and without having to be preceded by any access code.

Various telephone monitoring and security systems in accordance with the invention will now be described, by way αf example, with reference to the drawings, in which:

Fig. 1 is a block diagram of a telephone security system;

Fig, 2 is a block diagram αf a telephone monitoring and security system;

Fig. 3 is a flow diagram of the operation of the system αf Fig. 2;

Fig. 4 is a block diagram αf a modified security system; '

Fig. 5 is a block diagram of a modified monitoring and security system; and

Fig. 6 is a more detailed block diagram αf a portion αf Fig. 5. Fig. 1 - basic security device

The system comprises circuitry which is attached to a telephone line 10^' (which consists αf 2 wires) between the user's handset 11 and the telephone exchange 12, at a point near the handset 11. A convenient location is in the domestic junction box (not shown) which forms the junction between the exchange line and the user's equipment (one or more handsets, etc) , or at any other suitable junction box in the system. The system is coupled to the line 10 in two ways: a line reset unit 13 is connected in the line 10, and power and signals are tapped off the line 10 by a tap 14. The line reset unit 13 comprises means for breaking the line 10 between the handset 11 and the exchange 12, such as one or two relays or electronic switches.

The power for the domestic telephone user is provided from the telephone exchange. Vhen the telephone is not in use, the line 10 carries an open line voltage αf about 50 7. When the handset is lifted, this voltage drops tα a "lifted handset" level, which is about 3.5 V far certain older type telephones and about 10 V for certain newer type telephones. Other variations of voltage may also occur, e.g. for the ring signal and for speech signals. In particular, the dialling signals (for a dial type handset) are as follows. The line voltage level first drops sharply from 50 V tα the "lifted handset" level when the handset is lifted. As each digit is dialled, so the line is open-circuited for brief intervals to generate a series of 50 V pulses at about 100 ms period. Between successive digits, there is an interval, the inter-digit pause, of at least 800 ms.

The tap 14 feeds a power supply unit 20, which regulates the varying line voltage to produce a steady power supply for the rest αf the system.

The tap 14 also feeds a pulse detector 21, which recognizes the dialling pulses and filters out other signals. The dialled pulses are fed from the unit 21 to a pulse counter 22, which counts them to determine what digit is dialled. The unit 21 also feeds a digit detector 23, which detects the inter-digit pause and so determines when a digit is complete.

The unit 23 feeds a digit counter 24, which counts from 1 up to 4 and in turn feeds a fixed memory 25 in which a 4-digit code is stored, sα as tα read out the 4 digits αf the cade in succession. The memory 25 feeds a comparator 26, which is also fed with the output of the pulse counter 22, which stores the dialled digits in succession. Hence as long as the dialled digits match the code sequence, the comparator will indicate a match; as soon as the dialled sequence differs from the stored sequence, a mismatch will be indicated.

The digit detector 23 also feeds the pulse counter 22 via a reset line, to reset the counter 22 after each dialled digit has been counted and compared with the stored code digit. The signal on this line is also used to enable the comparator.

The digit counter 24 has two output lines 27 and 28 in addition to the output tα the memory 25. Line 27 is energized on each αf counts 1 to 3; line 28 is energized an count 4. Line 27 feeds an OR gate 30 via a switch 29; line 28 feeds this OR gate directly, and this OR gate feeds a one-shot circuit which in turn controls the line reset unit 13. Switch 29 is set open or closed, as desired, when the system is installed. If it is closed, then the αne-shαt 31 will produce a pulse for each digit dialled, just after the digit has been dialled. This pulse will operate the line reset unit 13 to briefly open the line 10 after each digit is dialled, so that the exchange 12 will "see" 4 separate single-digit diallings, with a hang-up signal after each, and thus make nα response. If the switch 29 is set open, then the exchange 12 will "see" a dialling signal αf 4 successive digits, followed immediately by a hang-up signal. In either case, the dialled sequence will normally have no effect at all as far as the exchange is concerned, because of the hang-up signal or signals. However, if switch 29 is set open and a valid sequence of only 3 digits is dialled, the exchange will respond normally tα that. Thus 3-digit calls, such as emergency and operator calls, can be made if the switch 29 is set open.

The comparator 26 feeds a flip-flop 35,- which is initially in the reset state and is switched to the set state by any mismatch signal from the comparator. The reset output of the flip-flop is fed, via an ABO gate 36 which is enabled on the 4th count of the counter 24 by the line 28, to inhibit inputs to the pulse counter 22 and the digit detector 23. Thus if the 4 dialled digits match the stored 4 digit code, the flip-flop 35 will still be in the reset state after the 4th digit, and the AST; gate 36 will be enabled on the 4th digit, to pass an inhibit signal from the flip-flap 35 ta the pulse counter 22 and the digit detector 23 to inhibit them from responding tα any further - e -

dialled pulses. Thus if the correct 4 digit code sequence has been dialled, the system will not respond to any further digits, so that the sequence for the desired number can be dialled successfully. However, if the code sequence was wrong, the system will continue to operate as before (with counter 24 counting cyclically) to look for the correct sequence,- nd will disconnect the call by means αf the line reset unit 13 after every digit αr every 4th digit, depending on the setting αf the switch 29.

The tap 14 also feeds a call detector 38, which detects whether or not a call is in progress. This unit feeds a delay circuit 39, which has a delay of 10 s. If unit 38 detects that a call has ended, the delay circuit 39 is triggered, and after the 10 s delay it emits a reset signal tα the whole system, so that any further call is treated as described above. However, if a further call is detected within the delay period, the reset signal is not generated and the new call can therefore be dialled in the normal way, without having tα be preceded by the code sequence.

The system as described operates with dial-type telephones, and with keypad telephones of the type which generate sequences αf pulses corresponding to those from dial-type telephones. For tone signal telephones, the system would operate in the same general manner, but the pulse detector 21, pulse counter 22, and digit detector 23 would be replaced a a digit detector and decoder unit which would detect the occurrence of dialled digits and decode them, feeding the counter 24 and comparator 26 as before.

The system obviously has no effect on incoming calls.

If the system is fitted as a unit in the master junction box of an installation with several telephones, it will control all of them. It is possible to install a second unit in one of the other junction boxes αf the system, so that a call from a telephone connected tα that other junction box can only be made by first dialling the two access codes for the two units in succession. The second unit in this case will need some farm of temporary power storage, such as a small rechargeable battery, because the first unit will effect brief disconnections of it from the telephone line from the exchange.

The system has been decribed so far as fitting in an existing telephon junction box. Various other forms of the system are possible. For example it can be made as a security box which fits over an existing plug box (i.e. a box which a telephone can be plugged into), having a plug an its rear face which plugs into the plug box and a corresponding socket on its front face. It may be fixed in position by having a portion extending beyond the plug box so that it can be screwed to the wall aver the plug bax, by having self-tapping screws which can be screwed into the front of the plug box, or by having screw holes aligned with the screws of the plug box so that those can be taken out and put back in through the. security box as well as the plug box ⁽or replaced by longer screws if necessary).

It can also be fitted adjacent to the plug box, with a wire connector to the plug box. This arrangement is obviously liable tα have the connector unplugged from the plug box and the telephone unplugged from the security box and plugged into the plug box. Various forms αf locking for the connector may be used tα combat this. Alternatively, the security box can incorporate a disconnect indicator, which comprises a circuit which detects if the telephone line power is disconnected for more than a few seconds and thereupon triggers a visible alarm which automatically remains on for a suitable time, e.g. a day. The security box must obviously include a battery power supply for this; a rechargeable battery energized through a trickle charge circuit from the telephone line is suitable.

These arrangements, using the circuit of Fig, 1, will however obviously only give protection to a telephone plugged into the particular plug box involved.

The system has been described in terms of separate functional elements, but (as also for some αf the systems described later) certain αf the functions can be performed by a suitably programmed microprocessor.

If the system is constructed as a box or plate which is accessible, it may be provided with disabling means which are key-operated. Turning the key would operate a switch which could for example be placed between the gate 30 and the one-shot 31, or to connect a steady logic 1 to the inhibit inputs tα units 22 and 23. Fig. 2 - basic monitoring system

Referring now to Fig. 2, there is shown a system comprising a telephone security system 15, recording means 70, and a host computer 100. The security system 15 is broadly as described with reference tα Fig. 1, and corresponding references are used. However, the present system differs in certain respects from the system αf Fig. 1, as fallows.

First, the memory 25' is now a changeable memory, and its contents can be changed by means αf interface logic 45 which is fed with signals, from the recording means 70, on a line 46 which enters the security system through a dual buffer (eg an RS232 buffer) 47. The memory 25' may be a conventional RAM, but is preferably a reprogrammable ROM of a type which will retain the stored digits in the event of a momentary power failure. Also, the power supply 20* is modified to accept power from a line 48 from the recording means 70. Additional power is fed into the security system via the line 48 when the memory 25' is being reprogrammed and the power required is greater than can be supplied by the power supply unit from the line 10'.

Second, a resettable one-shot circuit 50 is provided, feeding an OR gate 51 which is connected between the AHT) gate 36' and the two units 22' and 23' which the gate 36' feeds. The one-shot 50 is fed from the recording unit 70 via a line 52, and is used tα turn the security system on and off - that is, to enable or disable it. Provided that pulses are supplied on line 52 at a sufficiently high rate, the one-shot 50 will be kept reset and its output will remain low, so that the security unit will function as previously described. However, if the pulses on line 52 cease, the one-shαt 50 will set, after its preset time interval. Its output will thus go high, and the functioning αf the security unit will be inhibited, so that calls can be made without the access code having tα be dialled first. Thus the recording unit 70 can inhibit the security system by sending pulses and enable it by ceasing to send pulses; and the security system will also become enabled, as a default condition, if the recording unit 70 loses power.

As an alternative, a conventional flip-flop may be used in place αf the resettable one-shot 50, with its state being toggled by signals from the recording unit 70. A power monitor unit (not shown) would also be provided, to monitor the voltage from the recording unit 70 on the line 48 and force the security unit into the default state ⁽calls only allowed if the access code is dialled) in the event of a power loss in the recording unit 70.

Thirdly, the call detector 38', which detects the end of a call, has its output fed via a line 54 tα the recording unit 70. Also, a ring detector circuit 55 is provided, fed from the lines 14' and feeding the recording unit 70 via a line 56. This circuit 55 detects the ringing signal, ie the interval between the end of dialling and when the called telephone is picked up.

The recording means 70 comprise a microprocessor 80 and associated apparatus, all mounted on a board (an "intelligent board") which can be fitted inside a commercially available microcomputer such as an Apple ⁽RTM⁾ or an IBM PC (RTM) or a minicomputer or mainframe computer, or mounted in a self- contained unit which can be coupled tα an expansion port on a computer such as the A strad PCV8256 or 8512 (RTM) which does not have space inside for an extra board. The computer to which the recording means 70 is coupled is shown as a host computer 100.

The unit 70 has a power supply consisting of a mains-energized power supply unit 71, a battery back-up unit 72 energized from the unit 71, and a selector unit 73. The unit 71 may be omitted if the host computer is of the type which can supply power tα the unit 70. The battery unit 72 and selector unit 73 can also be omitted if the host computer is of the type which can be put into a stand-by mode in which it continues tα provide such power while its main functions are turned off and one can be confident that the host computer will not be completely shut down. It is generally desirable for the recording means 70 to operate continuously, 24 hours a day, whereas the host computer may be turned off (at any rate as far as its main functions are concerned) outside normal office hours. The unit 73 also supplies power tα the line 48 tα the security unit 15. Isolation means (not shown) may be provided to ensure that damaging signals dα not get into the security unit and thence onto the telephone line 10' even in the event of a fault in the recording unit 70. Such isolation means may comprise a relay in the line 48, and possibly the connection αf line 48 to the battery unit 72 rather than the selector unit 73 and the provision αf a further relay (not shown) between the power supply unit 71 and the battery unit 72, which is open when the relay in line 48 is closed,so that there is never a direct path from the power supply unit 71 through the battery unit 72 tα the security unit. The microprocessor 80 is coupled tα a data bus 81, a control bus 82, and an address bus 83. These buses have coupled to them a timer 84, a programmable read-only memory PROM 86, a random access memory RAM 86, and interfacing means - a multiplexer 88 and a buffer 89 - with the security system 15. The host computer • 100 is coupled to the unit 70 by means of an input/output unit 90, also coupled tα the buses 81 to 83.

The buffer 89 is an RS232 buffer 89 corresponding to the unit 47 for the lines 46 and 53. The multiplexer MUX 88 is controlled by the control and address bus 82. The multiplexer 88 is also coupled, via lines 90, tα further interfaces (not shown) which are in turn coupled tα further recording means (not shown). This enables the unit 70 to monitor several telephone lines. Of course, if only a single line is to be monitored, the buffer 89 will be coupled directly to the bus 81 and the multiplexer 90 will be omitted.

As an alternative, a serial tα parallel converter (not shown) may be provided in the unit 70, fed from the line 53. The microprocessor 80 would monitor its output for changes, and would accept its output as representing a digit if it remained unchanged for a sufficiently long time (eg 500 s; the justification of this figure is discussed below) . The output so accepted would be stored in the RAM 86, and the counter reset in readiness to start counting the pulses for the next digit (if any). Because of the difference in the operating speeds of the security system 15 (in which events typically occupy a considerable number αf milliseconds) and the recording unit 70 (in which the cycle time is of the order of a microsecond), it may be necessary to provide an interface adapter unit (not shown) between the bus 81. (A similar unit may also be required between the input/output unit 91 and the host computer 100.)

The transmission αf the dialled digits from unit 15 tα unit 70 may alternatively be achieved by using a serial tα parallel converter as just described, and feeding line 53 from the pulse counter 22' via a parallel to serial converter (not shown) in the unit 15.

The PROM 85 contains the programs which control the operation αf the unit 70, and specifically the operation of the microprocessor 80. The timer 84 contains a continuously running date, day αf week, and time αf day timer, which is initially set from the host computer 100. This timer enables the duration of a telephone call tα be recorded, and it also enables the date, day of week, and time αf day at which the call is made tα be recorded. The RAM 86 is used tα accumulate records of calls made - the number called, the call duration, and the time of day. Obviously, the number called and signals indicating the start and end αf the call are obtained from the security system 15. The information stored In the RAM 86 can be passed tα the host computer 100 via the unit 91 when requested by the host computer. The RAM 86 also stares certain control data which is used by the system.

Fig, 3 - operation of Fig. 2 system

Fig. 3 is a flow diagram for the system of Fig. 2, indicating the main functions which the microcomputer 80 performs. These can be divided into two main groups; functions involving interaction with the host computer 100 (and therefore reflected in corresponding functions of the host computer), and functions which the unit 70 performs in conjunction with the security unit 15.

The program may conveniently be arranged to start with block 110, which is a test block which tests the input from the host computer 100 tα determine whether or not the system is to be initialized. If it is, then a system disc is inserted into the host computer and run, and appropriate data (control information⁾ is transferred from the host computer to unit 70, block 111. More specifically, the control data in the RAM 86 is replaced by fresh control data from the host computer.

The next test, block 112, determines whether the access code is tα be changed. If it is, then the new access code is typed into the host computer, transferred tα the unit 70, and transferred from there tα the security unit 15 tα change the contents αf the memory 25'. Of course, each security unit 15 will have its own access code and other control data.

The next test, block 114, determines whether new times (time of day, day αf week, date, and the times for enabling and disabling the security unit 15) are to be entered. If the time settings are tα be changed, then they are entered into the host computer and transferred to the RAM 86, and the timer settings are then used to reset the timer 84. The setting αf the timer may be checked far correctness against the new setting entered from the host ~ -

computer before it is reset. The security unit 15 can be set tα the operating state, in which it operates to permit a call to be made only if it first detects the security code, or to the off state, in which it allows all calls to be made. The start αf day time is set tα the start αf normal office hours and the end αf day time to the end αf normal office hours; the date and day αf week data may also be used tα allow selected days (eg weekends) and dates (eg Bank holidays) tα be treated specially.

In block 114, the microcomputer determines whether the current time, as indicated by the timer 84, has passed the start αf day time or the end of day time or a special day or date. If it has, then block 115 is entered, and control pulses are sent via the multiplexer tα the security unit 15 if it is to be set into and kept in the operating state. There can of course be different start and stop times far different security units.

The next test, black 116, determines whether the recording unit 70 is ta start monitoring the calls made. If it is not, then the next block is block 117, which tests whether αr not the settings are tα be changed. If they are, then block 110 is entered; if not, the system cycles between blocks 116 and 117 until monitoring is to be started. The test of block 116, αf course, involves checking the host computer to determine whether it has been set to cause monitoring to start. If the test in block 116 is satisfied, the program enters block 125, which tests the signals from the security unit tα determine whether dialling has started; ie whether a pulse has started on line 53. If no call has been started, black 118 is entered to see whether an interrupt signal from the host is present. It such an interrupt signal is present, the recording unit 70 determines whether the host computer is requesting the transfer αf the recorded information for the calls made, block 119. If it is, then that information is transferred tα the host computer 100, block 120, and black 110 is returned to. If no information transfer is being requested, then black 110 is returned ta direct from block 119. If there is no interrupt from the host computer, then the unit 70 cycles between blocks 125 and 118.

The program so far has involved the host computer 100 as well as the monitoring unit 70, though αf course some of the actions in blocks 113 and 115 have been between the recording unit 70 and the security unit 15. Once the recording αf calls is to start and a call is actually started, the program enters a phase which in substance involves only the recording unit 70 and the - 43 -

security unit 15. Block 125 can be regarded as the first block of this phase, since it is followed by block 126 if a call is found to have started. This test is made by monitoring the signals obtained from the security unit 15. If a call is found tα have started, the number called is recorded in RAM 86, the time at which the call started is taken from the timer 84 and recorded in the RAM 86, the time at which the call ends is temporarily recorded in RAM 86, and the duration of the call is calculated and recorded in the RAM 86.

More specifically, the recording unit 70 initially monitors the security unit by means of line 53 (block 125) to determine whether dialling has started. If it has, then the pulses from the pulse detector 21 are counted. The timer 84 is used tα measure the time interval between successive pulses. As long as the pulses appear at less than 500 ms spacing, they are part αf the train αf pulses representing a single dialled digit. (The nominal spacing of successive pulses of a single digit is 100 ms, the nominal interval between digits, the inter-digit pause, is 800 ms.) If this time is exceeded, then that digit is complete and either the next digit will follow or the full number has been dialled. The unit 70 therefore then checks the signal on line 56 from the ring detector 55 (block 127), tα determine whether dialling is complete and the called number is ringing. The unit 70 may start checking for the ring signal 200 ms after the end of a dialling pulse (assuming that a further dialling pulse is not detected before then) , tα ensure that the ring signal is not missed even if the called number responds immediately. Until the ring signal is detected, the unit 70 continues to monitor the line 53 tα determine whether there are any further digits being dialled, cycling between blocks 126 and 127. The time at which the call is started is taken as the time when the ring signal ends; this time is recorded temporarily in RAM 86 (block 128).

It is assumed that the timer 84 is capable of being used for timing intervals αf some milliseconds, as well as keeping time of day, day, and date, with the time intervals actually being measured by the microprocessor staring, in the RAM 86, the times of the start and end of the period tα be measured and then subtracting the first from the second tα determine the time interval. A separate interval timer cαuld αf course be used instead. However, such an interval timer cαuld not be shared between several telephone lines with their respective security units; a separate interval timer would be needed for each line. Once a call has been initiated, the ring tone has been detected, and the ring tone has ended (ie the called number has answered), block 129 is entered, and line 54 is monitored for the end αf the call. When the call ends, then (block 130) the time at which it ended is taken from the timer 84 and recorded in the RAM 86 and the duration αf the call is calculated from the call start and stop times and recorded in the RAM 86 (in place of the end αf call time, which is then deleted from the RAM 86).

From black 130, the system then checks whether the start αf day or end of day time has been passed (block 131), and if so, changes the control signal to the security unit tα enable or disable it (block 132). These blocks resemble blocks 114 and 115. The system then enters block 118, and either cycles between blocks 118 and 125 waiting for the next call, or goes tα block 119 if there is an interrupt from the host computer.

It will of course be realized that this specific flaw sequence is merely indicative of the functions which the system 70 has to perform; in practice, the details of the program may be arranged differently. In particular, the program would have tα be modified in conventional manner to incorporate multiplexing of various functions if the recording unit 70 controls more than one security unit. Also, αf course, the system may be modified so that an interrupt signal from the host computer can be responded tα at various points in the sequence αf blocks from 126 to 132, so that the stored information in the recording unit can be passed to the host computer without being held up if a call happens tα be in progress when the host computer calls for that information.

The host computer 100 contains programs for reprαgramming the recording unit 70, extracting information recorded in the unit 70, and displaying and analysing that information. The analysis program provides a call listing giving, for each call, the number called, the date, the time the call started, the duration αf the call, and the cost. The cost is calculated from a stared table giving costs in terms of time and area (local, national, international, etc). The display program is arranged tα provide a graphical indication αf the usage αf the telephone, eg the daily, weekly, monthly, or yearly usage pattern. A further analysis program may be provided, which comprises a stored list αf customer details, and checks the numbers called against that list so that the listing includes, far known customers, details αf the identity αf the customer (eg name and address) as well as merely the telephone number. - -

Fig. 4 - modified security device

The basic security device shown in Fig. 1 can be modified and expanded in several ways. Fig. 4 is a block diagram αf a modified circuit which provides additional functions, and provides protection for all telephones αf an installation without having to be connected on the exchange side of all αf them. Corresponding references to Fig. 1 are used.

The system of Fig. 4 is intended far use with a system having two (or more⁾ telephones 11A and 11B, and in which it is not feasible tα connect the system at a location between the exchange 12A and all the telephones. Thus the system is fitted in the line 10A at a location (indicated by the broken line 15A⁾ which is between one telephone 11A and the exchange but is not between the other telephone 11B and the exchange.

It is obvious that the system will operate to stop calls from telephone 11A in the same general manner as the system αf Fig. 1 operates. The system operates to prevent all calls from telephone 11B; thus outgoing calls can only be dialled from telephone 11A, though incoming calls can be received on telephone 11B, and calls initiated from telephone 11A can be continued from telephone 11B. Calls can αf course be made from telephone 11B if the system is disabled.

Tα achieve this, a small resistor 16 is connected in the line 10 in series with the telephone 11A. Substantial currents will flow through telephone 11A if a call is being made from that telephone. These currents will be detected by a current detector circuit 17, connected across the resistor 16, which will inhibit the operation of an extension inhibit circuit 18. This latter circuit 18 is fed from the pulse detector 21A and, if not inhibited, drives the one-shot circuit 31A via an OR gate 30A to repeatedly operate the line reset unit 13A. Thus if an attempt is made to dial a call from telephone 11B, -the system detects that a call is being dialled which is not from the telephone 11A, and generates interference pulses (by means of the line reset unit 13A⁾ which garble the number being dialled. If the call is being made from the telephone 11A, then this is detected by the current detector 17, and the operation of the extension inhibit circuit 18 is inhibited, so that there is normal operation far numbers dialled from telephone 11A. The line reset unit 13A includes a resistor 19 which is connected across the line 10 when the unit 13A is operated. The line voltage thus rises to less than the full open line voltage when the unit 13 operates. The operation αf the unit 13A is still sufficient tα garble calls from telephone 11B and to signal a hang-up and end αf call to the exchange 12A, but it is not sufficient to simulate an incoming call and induce a ring at the other telephone 11B. Without the resistor 32, the operation αf the system in response to the access code being dialled at telephone 11A may result the telephone 11B ringing briefly. This is liable to startle the user (although it does not affect the operation of the system) .

The system of Fig. 1 has two modes αf operation. In one, the line reset unit is only operated after the fourth digit of the access cade, sa that 3-digit calls can be dialled. This allows emergency calls (999 calls) to be made, but it also allows various operator-type calls to be made. Thus unauthorized calls can be made by calling the operator and obtaining them through the operator service. In the other mode, the line reset unit is operated after every digit αf the access cade. This prevents unauthorized calls being made by using the operator services, but it also prevents emergency (999) calls from being made.

The system αf Fig. 4 includes means for overcoming this drawback, b allowing emergency (999) calls but not other operator services. It als includes means far external programming of the access code, of a single numbe which is permitted without the use αf the - access code, and of a clock circui which is settable sα that the system is disabled for preset times αf day. I also provides means far call counting, with external readout αf the count.

The memory 25 A is constructed with three sections AC, PN, and EM, whic contain respectively a 4-digit access code, a multi-digit preset number, and th 3-digit emergency number 999. The counter. 24A is provided with an integra multivibrator and 2-bit fast counting section, sα that in response to an inpu pulse from the digit detector 23A, the fast counting section cycles through it 4 counts immediately after the main count αf the counter has been incremented All outputs αf the counter are fed tα the memory 25A, 3 αf the 4 counts αf th fast counting section being used to select the AC, PI, and EM sections of th memory 25A in turn. These three counts are also fed to three correspondin AND gates 32 to 34 tα which the output αf the comparator 26 A is fed, sα tha the outputs of these gates represent the results of the three respectiv " if -

comparisons of the digit which has just been dialled with the corresponding digits of the three stored sequences (access code, preset number, and emergency number).

The access code is thus compared with the dialled sequence by gate 32, and if the two sequences match, the flip-flop 35A will remain set at the end αf the four digits. As will be seen, the αne-shot 31A will be triggered and the line reset unit 13A operated far mast of these digits because the access code will not match the preset number or the emergency number. It is therefore not necessary tα feed the counts αf the counter 24A tα the one-shot 31A for each digit αf the access cade. It is however necessary to ensure that the one-shot 31A operates after the last digit αf the access code if the access code has been dialled. This is because the following number dialled ⁽the desired number) must not have any access cade digits preceding it; it must be preceded by a disconnect signal. The output αf gate 36A is therefore fed to OR gate 30A as well as tα the pulse counter 22A and the digit detector 23A. The output of gate 36A in effect "freezes" the system after the access code has been dialled.

The connection of the 4 count of counter 24A tα the OR gate 30A via the gate 36A, instead of direct, ensures that if the preset number is being dialled, this is not interfered with by an unwanted resetting resulting from the stored access code not matching the dialled digit sequence αf the preset number. This is because the flip-flop 35A remains set after the 4th digit, sα enabling the gate 36A, only if the access code has been dialled.

Of course, if the digit sequence being dialled does not match the access code, then the pulse counter 22A and the digit detector 23A will not be inhibited but will continue to operate, This means that the system can cape with a preset number which is longer .than the access code (which is 4 digits) , The counter 24A can count to the length αf the longest preset number which the memory 25A can hold, sα it will continue tα count up until it reaches its maximum ⁽equal tα the maximum design length for the preset number⁾, and then remain at that maximum count until the telephone handset has been replaced for a sufficient time (as detected by the call detector 38A, which detects when th line 10A is quiescent). Attempted comparisons of digits from the puls counter 22A with digits beyond the end αf the 4-digit access code or the 3 digit emergency sequence automatically fail. The AID gates 33 and 34 operate tα compare the current dialled digit with the corresponding digit αf the preset number and the emergency number respectively. Their outputs are combined by an OR gate 40, sα this OR gate gives a 1 output if the dialled digit matches either the preset number αr the emergency number. This gate feeds a pulse expansion circuit 41, which lengthens a 1 pulse fed tα it and feeds an inverter 42, sα a 1 from inverter 42 indicates that no match has occurred (i.e. with either the preset number or the stored number). An AED gate 43 is fed by the inverter 42, which is also fed^' by the digit detector 23A output to the counter 24A. The timings of the two signals tα the gate 43 are such that the pulse from the digit detector 23A is allowed tα pass through if there is a 1 output from inverter 42, i.e. if the pulse extender 41 has not received a 1 input, which means that neither the preset number nor the emergency number has been matched by the dialled digit. Thus as long as the dialled digit sequence matches the sequence αf the preset or emergency numbers, there is no output from the gate 43. As soon as there is a mismatch, however, the gate 43 will produce an 1 output, which is fed via the gate 30A tα the one-shot 31A tα operate the line reset unit 13A.

The preset number and the emergency number can thus be dialled out without interruption. It is also passible to dial out the preset number with any of its first 3 digits replaced by the corresponding digits of the emergency number ⁽999). However, this is not a serious defect of the system, because the ability to dial the preset number with such modifications is αf little use. If desired, the system can be modified sα that once a mismatch has occurred for either the preset number αr the emergency number, no further comparisons for that number are permitted. If the access cade is being dialled, then most αr all αf its digits will not match either the preset number or the emergency number, and sα will trigger the αne-shαt 31A, as noted above.

To prevent an unauthorized call from being dialled immediately after a call using the preset number or the emergency number, the delay circuit 39A, which delays the resetting of the whole system after a call ends, has the output of flip-flap 35A fed ta it. If flip-flop 35A is set, indicating that a call has been made using the access code, then the delay circuit 39A delays the system resetting; but if the flip-flap 35A is not set, indicating that an emergency αr present number call has been made, then the circuit 35A generates the system reset signal immediately on the end αf the call being detected. The system is controlled by a control unit 60, which is cαnnectable tα the system via a multiway plug and socket connector 61 with the .socket mounted on- the front of the bαx housing the system. The control unit 60 is not shown in detail; it may conveniently comprise a battery, an LCD display, a keyboard, a microprocessor, a PROM, a RAM, and a clock/timer unit (thus resembling a pocket calculator and a remote control TV unit⁾. A bus 62 from the connector 61 is connected to the memory 25A, sα that the access code and the preset number can be entered into it as desired. The memory 25A is a programmable memory, so that fresh access codes and preset numbers can be entered into it.

The system also includes a clock and timer unit 63 coupled tα the bus 62 and feeding an AND gate 64 connected between the one-shot circuit 31A and the line reset unit 13A. The unit 63 can be set from the control unit 60 tα disable the system for any desired periods during the day. (The unit 63 can thus also be used to disable the system completely, or a separate disabling unit may be provided instead αf or as well as the unit 63.) The system also includes a call counter 65, fed from the call detector circuit 38A and coupled tα the bus 62. The call counter 65 counts the number of calls made, and can be interrogated and reset by the control unit 60.

The control unit 60 can thus be used to determine how many calls have been made since it was last used, tα check the accuracy αf the clock portion αf the clock timer unit 63 and change the permitted periods controlled by the clock timer unit 63, to disable the system completely, to change the access code, and tα change the preset number. The changing αf the preset number allows the owner tα set the system sα that a baby-sitter, far example, can make calls tα a single number at which the owner can be reached but no other calls.

If desired, the system may include an access lack unit (not shown⁾ coupled ta the bus 62 ⁽or connected between the connector 61 and the bus 62⁾ which will allow the control unit 60 access to the system only if the access code is first entered from the control unit 60. The access lock unit would either use the access code stored in the memory 25A αr stare the cade internally as a separate copy. The control unit 60 would be constructed with a memory storing the access code, sα that the user would not have tα remember it. This stops unauthorized people from reprαgramming the system using another control unit. Figs. 5 and 6 - modified monitoring and security system

The basic monitoring and security device shown in Fig. 2 can be modified and expanded in several ways. Figs. 5 and 6 are block diagrams of a modified circuit which provides additional functions. Corresponding references to Figs. 1, 2, and 4 are used. The system αf Fig. 2 was shown as using and described in terms αf separate functional elements. In the system of Figs. 5 and 6, several of these functions are performed by a suitably programmed micro¬ processor.

Fig. 5 is a black diagram showing how the modified system is coupled tα a multi-line private exchange installation. There is a plurality of lines 101 from the public utility exchange (not shown) to a private branch exchange (PBX) 102, which may be either automatic or provided with operator control. The PBX 102 has a plurality of extensions 103 connected to it, and provides all the usual functions, allowing calls from one extension to another and between the extensions and outside lines (lines 101) .

The present system is attached to this installation via a plurality αf identical line units 15-1, 15-2, ... 15-n, one for each of the lines 101; the present system is thus wholly independent of and separate from the PBX 102. The units 15-1, etc. are all coupled tα a common monitoring and control unit 70A, which is in turn coupled to a host computer 100A, which can conveniently be a microcomputer. 'The units 15-1, etc can conveniently be connected by utilizing standard line connectors, which are normally present. The control unit 70A is conveniently mounted adjacent to these connectors, e.g. on a printed circuit board which plugs into them.

Fig. 6 is a block diagram αf line unit 15-1. There is a line reset relay 13-1 in the telephone line 10-1, driven by a relay drive control circuit 31-1; there is a line DC status detection circuit 21/38 coupled to the line 10-1 , which detects whether the telephone in on αr off the hook and also detects dialling pulses; there is a inward ring detector 67, which detects when the line is being used for an inward call by detecting a ring signal from the public exchange; and there is a charging pulse detector 68, coupled to a latching circuit 69, which detects charging pulses from the public exchange. The units 31-1, 21/38, 67, and 69 all effect conversion between line 10-1 level signals and logic level signals, and are coupled tα the control unit 70A via an interface 88A as indicated. The line reset relay is shown as a single simple αpen-and-close contact; however, a more elaborate circuit which gives a desired condition on the line (αr different desired conditions on the line as seen frαm the public exchange and the PBX 102⁾ can obviously be provided if desired, as was done in the Fig. 4 circuit.

The control unit 70A is broadly similar tα the control unit 70 of Fig. 2, having a microprocessor, control, address, and data buses, a timer, a RAM, a PROM, an I/O unit coupling the unit to the host processor 100A, a timer, and a multiplexer 88A (not shown) coupling the unit 70A to the units 15-1, 15-2, etc. The control unit 70A may also include means for monitoring the states of the external and internal (battery) power supplies, and signalling an alarm if either or both falls below a safe level. The unit 70A performs several of the functions performed by the hardware of unit 15 in the Fig. 2 system, e.g. counting the digit pulses on line 10-1. The additional functions provided by the present Figs. 5 and 6 system are provided by suitable programming, though of course they could be provided by pure hardware, just as the functions αf the Figs. 1 and 4 systems and many αf those of the Fig. 2 system are so provided.

To make a call, a user must first enter (dial) his extension number, αf 2 or 3 digits depending on the size αf the system. The call only reaches the lines 101 if it an outside call, of course, and which line it appears on is independent αf which αf the extensions 103 it originates from. The extension number is thus a logical extension number, identifying the caller, rather than a physical extension number. The extension number dialled is detected by the control unit 70A, which therefore knows which extension the call is coming from. The unit 70A thereupon automatically operates the line relay unit in the relevant line 100, sα clearing the line tα receive the next number dialled.

If the system, is in the disabled state, where it permits all calls tα be made, then it takes nα further active part in the call. It does however monitor the call, logging it by extension number, number called, time, length of call, and cost. At suitable intervals the log of all calls made is transferred to the host computer 100A, where it can be analysed in various ways. Listings can be produced and displays generated tα show such things as the usage and cost of a particular extension αr group αf extensions; the number, time and cost of calls tα a given number; and the variation αf usage for different times αf day. All calls are logged, whatever the state of the system. If the system is in the active state, it prevents certain calls from being made, and uses the extension number tα control the call. The use αf extension numbers by themselves is liable to reduce security considerably if the extension numbers are primarily the physical extension numbers, αr if they are logical extension numbers unrelated to the physical extension numbers but of only 2 or 3 digits (as a valid extension number can probably then be found fairly quickly by random trial). Tα overcome this, the extension numbers can be made sufficiently long so that they act as individual access cades; the security of a 6-digit code with 100 users on the system corresponds tα that of a 4-digit code for a single user. Alternatively, 2-digit or 3-digit extension codes can be used, with the users also having individual 4-digit access codes; the system will then require the access code tα be dialled after the extension number if the call being made is one which is restricted in some way - e.g. restricted for that extension number αr restricted for the time of day. The farmer arrangement requires access codes to be used at all times. The latter arrangement reduces the usage of access codes, but has the complication that the user must either remember when tα use his access cade or must accept that if he tries tα make a call during a period when the system is active and forgets to use his access cade, the call will be barred. (If he nevertheless uses his access code when he does not need tα, the system will recognize that the called number has started with the access cade and effect a disconnection after it, sα that he will obtain the number which he then goes on to dial.)

Either the control unit 70A or the host computer 100A can be arranged tα monitor calls tα recognize certain search patterns or exceptional activity which might be due to a more sophisticated search pattern.

It may be noted here that whenever the system is not disabled, it monitors all calls for the emergency number and allows those tα be made without interruption. Several such numbers can in fact be permitted, e.g. the standard ew ergency number 999 and other numbers such as a police station, a security company, etc.

The system preferably requires access codes to be used only in certain conditions, and these conditions are preferably in fact somewhat more elaborate than indicated above. The system can be arranged tα apply different security requirements at different times, sα that all calls are barred (except when preceded by the access cade far the extension number) outside normal office hours, local calls are unrestricted during office hours, and long-distance ⁽STD) and international (IDD) calls are restricted in dependence an the extension number. This is achieved as follows.

When the control unit 70A recognizes that a call is being made (by receiving the extension number), it first checks its timer (corresponding to timer 84, Fig. 2) to determine whether the time in inside αr outside normal office hours. If the time is outside, then it looks up the access cade far the extension number it has received. This information is held in a look-up table stored in the control unit's RAM (corresponding tα RAM 86, Fig, 2). The table may conveniently have a location far each possible extension number; this involves a slight waste αf space, but this is usually acceptable as long as a reasonably high proportion αf all passible extension numbers are actually used. Each location for an actual extension number includes the corresponding access code. The system then checks the next 4 digits dialled against the access code which it has looked up. As long as they match, it drives the relay control unit for the relevant line to disconnect after each of these digits, but then permits the following digits (the desired number) to be dialled freely. But if the access code dialled does not match the stored access code, the system disconnects the line after every dialled digit. If the caller is genuine but has made an error in his access code, he must hang up and restart the call from the beginning.

If the time is within office hours, then the system monitors the number being dialled and, if necessary, looks at two further entries in the look-up table, one for STD and the other for IDD (each of these entries being a single bit⁾. If the number starts with a digit which is not 0, then the call is permitted to proceed. If the call starts with the digits 01 and the third digit is not a 0, then the number is an STD one, and the call is permitted to proceed or not depending on the STD bit in the look-up table. If the call starts with the digits 010, then the call is an IDD one, and is permitted tα proceed αr not depending on the IDD bit in the look-up table. As noted above, a call which would be barred by this process is automatically permitted tα proceed if the extension number is followed by the correct access code.

The system can obviously monitor incoming calls, though since the information available from the line relating to such calls is limited, such monitoring will not usually yield a great deal αf useful information. If the PBX 102 has a direct extension dialling facility, then the extension number will αf course be available to the system, and can be lagged together with such details as the time and length of the call.

In many multi-line private exchange installations, certain incoming lines are dedicated far special purposes, e.g. for facsimile machines and for mode s. Monitoring such dedicated lines suffers in general from the same problems as the monitoring of ordinary incoming calls. However, monitoring dedicated lines connected tα modems permits an important function. A modem and its dedicated line are normally used to permit outside access tα a computer. The present system can readily be arranged tα monitor such a line for calls, and tα take action dependent on the time of day. If the call occurs within normal working hours, nα action is taken. However, if the call occurs outside normal working hours, the present system can readily be arranged tα repeatedly operate the line reset unit In the line. This will garble any instructions or enquiries being passed into the modem from outside, and will also garble any information which is generated in the computer and passed out dawn the line. Thus the system will prevent any use of _t the dedicated line outside normal office hours ⁽or other set periods) . Normal security measures must, of course, be used to prevent unauthorized access to the computer during normal office hours, but these can be designed to allow operator monitoring.

It will be clear that more elaborate call control can readily be achieve by elaboration of these principles.

Claims

- 2S -C AJ2S

1. A telephone monitoring system characterized by detection means (21-23) for detecting, on a telephone line (10), a code sequence dialled from a telephone ⁽11⁾, and an interrupter (13) fitted in the telephone line and operable (via 31) under the control αf the detection means when the cade sequence has finished.

2. A telephone security system comprising a monitoring system according tα claim 1, characterized by comparison means (26, 35), associated with the detection means, operable tα repeatedly operate the interrupter if the dialled code sequence does not match a stored code sequence (at 25).

3. A telephone security system according to claim 2, characterized by means (24, 27, 30) for operating the interrupter after each digit αf the code sequence.

4. A telephone security system according to claim 2, characterized by means (24, 28, 30) for operating the interrupter only after the last digit αf the code sequence.

5. A telephone security system according to any one αf claims 2 tα 4, characterized by delay means (39) far inhibiting the operation of the system for a predetermined period after the end of a call,

6. A telephone security system according tα any one αf claims 2 tα 5, characterized by a memory (25A) storing a code sequence and at least one other sequence (PN, EM), in that the comparison means (26A, 32-35, 40) further compare the dialled sequence with the other stored sequence αr sequences, an by means (40-43) for inhibiting the operation of the interrupter if the furthe comparison matches.

7. A telephone security system according tα claim 5 and 6, characterized i that the operation of the delay means (39A) is inhibited if the match was wit one of said other sequences.

8. A telephone security system according to any one αf claims 2 to 7 characterized in that the memory (25⁾ is -programmable, and by a detachabl control unit ⁽60⁾ far entering at least one further sequence into it.

9. A telephone security system according tα claim 8, characterized in tha the detachable control unit stores the code sequence and the security syste accepts instructions from it only if the code sequences in the security syste and the control unit match.

10. A telephone security system according tα either αf claims 8 and characterized by a clock/timer unit (63) programmable from the control unit an operable tα inhibit the operation αf the interrupter.

11. A telephone security system according to any one of claims 8 tα 1 characterized by a call counter (65) which can be read by and reset from t cαntrαl unit.

12. A telephone security system according tα any one αf claims 2 tα 1 characterized by means ((16-18) for detecting a call being made from anoth telephone (11B) in the installation, and thereupon operating the interrupter garble the number being dialled.

13. A telephone security system according to any one of claims 2 to 1 characterized by a power supply unit (20) energized from the telephone line.

14. A telephone monitoring and security system according to claim characterized by means (70A, 100A) for lagging the cade sequence, the fallowi desired number dialled, the time, the length of the call, and/αr the cast af t call.

15. A system according to claim 14 characterized in that the system compris a plurality αf telephone lines each with a respective interrupter ⁽13', etc⁾, a multiplexing means (88) coupling a single cαntrαl means (70⁾ to all the lines.

16. A system according tα claim 15 characterized in that the cade sequen starts with an extension number, and in that the control means ⁽70⁾ thereup lαok up information associated with the relevant extension number from a loo up table.

17. A system according tα claim 16 characterized in that said information includes an access code and bits indicating whether predetermined types αf call (STD, IDD) may be made without being preceded by the access code.

18. A system according to claim 17 characterized in that the cαntrαl means includes a clock/timer (84) and controls which types of call may be made in dependence on the time.

19. A system according to any one αf claims 15 tα 18 characterized in that the control means (70) stores at least one other sequence (PN, EM) and permits direct dialling αf such a sequence αr sequences,

20. A system according tα any one αf claims 15 tα 19 characterized in that the cαntrαl means monitor dedicated lines and, on detecting an incoming call on such a line, repeatedly operate the associated line reset means in dependence on the time.