United States Patent 3865984

A system for controlling the operation of a plurality of electrical actuating devices, located at diverse points, from a remotely located control station via the conventional communication or telephone lines. Direct current voltage is transferred from the remote station to the local stations wherein the power is conservatively utilized in a circuit to control and power an electro/mechanical device normally requiring much greater voltage. The voltage is also modified and retransmitted over the same line back to the control station as signals indicative of certain conditions. In a preferred embodiment the device actuated is a mechanical bolt for securing the doors of any one of a plurality of protected premises. The bolt alternatively being operative from a locked or an unlocked position by a solenoid energized by a circuit utilizing the voltage transferred from a supervisory control station. The voltage received at the local protected station is modified and returned via same lines to indicate to the supervisory control station, by distinctive signals, the bolt and door position. The interconnected lines also monitor sound and maintain a two-way communication system. The voltage transferred is a moderate to low direct current voltage from a power source at the control station. No local power is needed or utilized at the plurality of local stations.

Application Number:
Publication Date:
Filing Date:
Primary Class:
International Classes:
H04M11/00; H04M11/04; (IPC1-7): H04M11/00
Field of Search:
179/1H,2A,37 340
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Primary Examiner:
Claffy, Kathleen H.
Assistant Examiner:
Popek, Joseph A.
Attorney, Agent or Firm:
Cennamo Kremblas & Foster
What is claimed is

1. A closed loop system for controlling the actuation of an electrical or electro/mechanical device on one or more local stations from a single control station utilizing a single pair of communication wires comprising:

2. The system of claim 1 wherein said electrical or electro/mechanical device is a lock for a door and wherein said electrical actuating device is a solenoid.

3. The system of claim 2 further comprising relay means for applying said stored voltage to said solenoid.

4. The system of claim 3 further comprising means for controlling the energization period of said relay.

5. The system of claim 4 wherein said means, having an energization period, is a capacitor connected in series with said relay means.

6. The system of claim 5 further comprising a transistor circuit connected to said relay, and wherein said relay energization period capacitor is connected to said transistor circuit wherein a discharge of said capacitor causes said transistor circuit to conduct which in turn activates said relay to apply said stored voltage to said solenoid.

7. The system of claim 3 wherein said means connected to said actuating device is a first switch connected to said door having a first position indicative of said door being open and a second position indicative of said door being closed.

8. The system of claim 3 wherein said means connected to said electrical or electro/mechanical device further comprises a second switch connected to said lock on said door having a first position indicative of said lock being locked and of a second position of said lock being unlocked.

9. The system of claim 7 wherein said tuning circuit means includes tuning parameters representative of said door open and representative of said door closed; and wherein said first switch means connects said parameters to said signal generator to control its period of oscillation in accordance with said door being open or closed.

10. The system of claim 8 wherein said tuning circuit means includes tuning parameters representative of said lock locked and representative of said lock unlocked; and wherein said second switch means connects said parameters to said signal generator to control its period of oscillation in accordance with said lock being locked or unlocked.

11. The system as set forth in claim 1 further including means at said control station for visually and audibly indicating said states of actuations.

12. The system as set forth in claim 1 wherein said communication wires are the standard utility telephone lines and wherein the local stations further include switch means for indicating to said control station the position of said electrical or electro/mechanical device and for connecting a handset telephone to said telephone lines for indicating said connection.

13. The system as set forth in claim 7 wherein said first switch means further include a pair of switch means positioned adjacent said door for indicating to said control station the door position and for connecting a handset telephone to said telephone lines.

14. The system as set forth in claim 12 wherein said switches further disconnect a handset upon connecting the other of said handset, and to interconnect both of said handsets when said system is in standby.

15. The system as set forth in claim 1 further comprising a monitor station at said control station and a monitor station at each of said local stations.

16. The system as set forth in claim is further comprising sound monitoring apparatus and means connecting such apparatus to said monitor station and to said monitored station.

17. The system as set forth in claim 15 further comprising switch means for sound monitoring of said stations during standby periods.

18. The system of claim 13 wherein said indication is an audible tone returned to said control station.

19. The system of claim 1 further comprising condition monitoring stations connected to said communication wires in said control station and in said local station, and means in said control station to indicate said condition.

20. The system of claim 1 further comprising a security circuit interconnecting switch means to prevent tampering.


The security of a premise whether it be a bank, manufacturing plant, or an office building, is a problem. The lock and key has continued to be the means for securing the premises. Improvements on the lock and key retain the inherent disadvantages and are cumbersome, expensive, and difficult to install.

Other securing means such as a key, coded card, or combination lock are still inherently subject to tampering, picking, being lost, may be used at any time, and may be had by former employees. Further, the lock being locked or unlocked does not necessarily mean that the door is open or closed.

Supervisory communication systems have been utilized in the prior art to effect a control function--including the securing of premises-- over conventional telephone or communication lines. Certain of these systems require modification of the telephone line and interfere with the normal operation of the line. Certain of these systems are powered from the ringing pulses and others are operative from a transmitted alternating voltage and/or pulses requiring very sophisticated and costly circuits. This is especially true when the punched card or coded pulses are used. All of these prior art systems are susceptible to spurrious signals and noises and each must have a source of local power for operation at the local actuating station.

The control system of the present invention overcomes the above-enumerated attendant disadvantages, is considerably simpler, fool-proof, and less costly.


The present invention provides a means of remotely locking and unlocking a door with a signal transferred via a communications line on which a two-way communication is maintained. Position signals are generated from voltage received and returned via the same communication lines to indicate whether the lock is locked or unlocked and the door is open or closed. Relatively large forces are generated at each door lock with no local voltage. All local stations are monitored at the control center; loss of voltage at any local station or an attempt to activate the door will immediately be detected at the control center.

In the preferred embodiment the control station utilizes the conventional or communications line to communicate with the plurality of local stations. Direct current voltage is also transferred over the same lines to activate a solenoid to cause a bolt to move in one direction or another. Circuitry is provided as a storage and timing function to utilize the low voltage to accumulate and activate a mechanical member requiring a substantially greater power. Circuitry is also provided to modify the received power into signals indicative of the locked door, unlocked door, open door and closed door. These signals are returned from each local station via the same communication lines to the control station.


It is the principal object of the present invention to provide a system for controlling a plurality of local electrical actuating devices from a control point utilizing communication lines.

It is a further object of the present invention to utilize voltage actuating devices having no local voltage requirements.

Another object of the present invention is to transfer from the remote station, to the plurality of local stations, the necessary power to actuate an electro/mechanical device.

Another object of the present invention is to convert the received power at the local station to several signals indicative of certain conditions, and to retransmit the signals back to the remote station.

Another object of the present invention is to utilize the received low voltage at the local station in a voltage accumulator and timer voltage supply for actuating electrical devices normally requiring a substantially greater power.

Another object of this invention is to provide voice communication, signaling and monitoring circuitry so efficiently as to allow their use without impeding the storage of power for operating the device.

Further objects and features of the present invention will become apparent from the following detailed description when taken in conjunction with the drawings in which:


FIG. 1 comprised of 1A and 1B is a schematic illustration of the fundamental concepts of the invention illustrating in block in two parts--the command monitor station A and the monitored-locking station B.

FIG. 2 is a schematic circuit of the control station monitoring functions.

FIG. 3 is a schematic circuit utilized at the local station for accumulating and timing the received voltage into sufficient power for actuating a solenoid normally requiring a much greater power; and a schematic circuit of the station for converting the received voltage to condition representative signals.


Reference is now made to the two-part block-schematic illustration of a preferred embodiment of FIG. 1. That shown left of the dotted line divider and designated as A (on a first sheet) is the command/control/monitor station. This is the remote point for controlling the operation of an electrically actuated device positioned at several local points. That shown right of the dotted line divider and designated as B (on a second sheet) is the monitored and actuating station. This is one, of which there may be several, local stations to be controlled.

As shown generally in FIG. 1, the preferred embodiment is illustrated as a door opening and closing system. It is to be understood, of course that the system is equally applicable to any other remotely located electrical or electro/mechanical mechanism to be controlled from a central station.

The system as shown is a closed loop system--that is, a single voltage source provides a voltage that is transferred over the telephone or communication lines. At the local stations the voltage is modified to reflect certain condition and returned over the same lines to indicate execution of the control function, a change in position or tampering. No local power is utilized at the local stations.

The voltage source in this embodiment is 48 volts direct current. It is a low voltage that may be permissably transferred over telephone or say 22 gage communication lines. And, in that it is direct current, there is no effect on the communication acoustical alternating signals normally transferred over the telephone lines. Further, the telephone lines are no way altered and remain telephone lines for the purpose of voice communication.

At the control station or remote point a two wire connection places the 48 volts from source 12 on the telephone or communication line 16; and at the monitored station B the 48 volts-- via the telephone lines 17-- is connected to the bolt 37 actuating mechanism 13. The bolt actuating mechanism 13 also modifies a signal generator 19 whose signal output in turn is transmitted back via lines 17 and 16 to the control station A. In this way the loop is completed.

Referring now to FIG. 1 with particular reference to each function illustrated in block. The telephone lines 16 and 17, handset or sound amplifier transmitter 20 and speaker 50 in the remote control station A, and the telephone handsets 51 and 53 positioned on either side of the door 11 are the essentials of the conventional voice communication circuitry.

To initiate operation of the remote controlled door lock system, switch 31 or 33 in the local station B is depressed to cause momentary loss of contact. These switching circuits (shown schematically in FIG. 3) provide the function of signaling the control center A, connecting its respective telephone handset to the telephone lines 17, and of shunting out the other telephone handset. The momentary break in the circuit is recognized by the lighting of pilot light or lamp L1 on panel 10 of the control station A. Return voice communication is had be depressing S1 on the control panel 10. The purpose of shunting either telephone handset 51 or 43 is to assure privacy in communication when the one is connected to the control station. The system can also provide sound monitoring using the same components as for voice communication--above described--and still accomplish the same functions. In this case, during the monitor or standby periods, the contacts of the switches 31 and 33 are in an up position and both handsets 51 and 53 are connected in series-- as opposed to the previous description wherein they were not connected during the standby period. Thus, sound monitoring is provided as transmitted by one or both telephone handsets. Pushing either switch button 31 or 33 will still create a momentary open circuit, signaling the control center A as noted above and shunting the opposite handset. This is shown in the alternate connection schematic of FIG. 3 a.

In addition to voice communication, the system is compatible with, and provides connection for, other conventional sound monitoring or frequency shift control equipment. This connection is shown as monitor 25 at local station B with its input/output 23. And as monitor 24 at control station A with its input/output 22. In either instance, connection is obtained by using a universal type transformer; one winding of which is connected in series with the line 16 and 17, the opposite winding being connected to input/output 23 or 22.

A security circuit 35 interconnects both switches 31 and 33 to prevent tampering or cutting of the handset wires--from causing operation. The security circuit 35 of FIG. 1B shown as item 55 in FIG. 3.

The volume control V on panel 10 of control station A connects the 6VDC power supply to amplifier transmitter 20 and controls its amplification level. Push to talk switch S1, in its normal position, connects speaker 50 to the output of amplifier 20 while connecting the input of amplifier 20 to line 16. When S1 is depressed it connects 50 to the input of amplifier 20, while connecting the output of amplifier 20 to line 16. Thus, in the normal position of SW1 speaker 50 monitors all audio tones received on line 16 and in the depressed position of SW1, speaker 50 will transmit to line 16 all audio sounds generated at the speaker. This accomplishes standby audio monitoring and two-way voice communication.

Gate circuit 28 is operative to turn on SCR 30 and 36 in the absence or normal standby current on the line. When either signal button 31 or 33, at the door in the local station B is depressed, the voltage drop in the line will become smaller than normal--thereby causing the gate circuit 28 to become less conductive. At this point a larger portion of the power supply voltage will be applied to SCR 30 causing it and 36 to switch on. SCR 36 in turn lights the red indicator pilot light L1 and turns on the audible oscillator 38. This will occur even if the event occurs for only a fraction of a second.

Gate circuit 32 is operative to turn on SCR 40 and the green monitor lamp L2. The SCR 40 is switched on--as explained hereinafter-- as the current flow decays to a steady state--thereby indicating readiness for another cycle.

Gate circuit 34 is operative to turn on SCR 36 when an audio pulse or other noise is received. SCR 36 in turn lights the red indicator pilot light L1 and turns on the audible oscillator 38.

The reset switch 18 resets the pilot lights L1 and L2 by momentarily opening the normally closed circuit. If the signal originally energizing the pilot lights has been removed the indicator lamp will reset or extinguish.

Lock switch 42 when lever S3 in the control station A is depressed is operative to activate the lock mechanism in the local station B. Normally the switch 42 maintains continuity of the negative side of the 48 volt d.c. line--telephone line 16. When the switch is moved to another position and then back, it momentarily disconnects the negative and connects it to the positive side of the line. When the switch returns to its normal position, the lock mechanism is activated.

With reference to FIG. 1B, the locking mechanism actuation circuitry 13 and the signal generation circuitry 19 together with the door 11 and locking mechanism form the essential elements of the local station B. The primary components are the actuation circuit 13, solenoid 39, and positive acting bolt 37. Fundamentally the 48 volts direct current applied to the communication lines is insufficient to activate a solenoid having a size to provide a powerful positive action. In accordance with the general concepts of the invention, the low power transmitted is applied to a power accumulator in actuation circuitry 13 and then applied instantaneously to the solenoid as a burst. The details of the gating and storage circuitry are described later with reference to FIG. 3.

Continuing with FIG. 1B the solenoid 39 includes the mechanics for moving the bolt 37 in a way such that each time solenoid 39 is activated it alternates from a locked to an unlocked position and vice versa. The solenoid together with the mechanical linkage for the bolt 37 is described in detail and claimed in my co-pending patent application filed herewith.

The signal generator 19 is controlled in its output by an oscillator circuit operable at three distinct frequencies. A high speed 27, medium 47, and low speed 45 tuning circuit is connected to the oscillator circuit--depending on the position of the door 11, lock bolt 37 and perimeter protection switches 21. During standby the oscillator 19 is quiescent.

Switch 41 is physically connected to the door 11 and may be magnetic-reed switch with its fixed position mounted on the door frame and movable portion mounted on the door itself. When the door is closed the switch is open and when the door is open the switch is closed. When the switch 41 is closed it connects the slow speed tuning circuit 45 to the signal generator 19 to cause the oscillator to oscillate and thereby transmit, via lines 17, a slow speed pulse.

Switch 43 is physically positioned adjacent and activated by the locking bolt 37. This switch is closed when the door is unlocked connecting the medium speed tuning circuit 47 to the signal generator 19 to cause the oscillator to oscillate and thereby transmit via lines 17, a medium speed pulse.

Perimeter switches 21 may be either magnetic-reed switches or mechanical switches. These switches connect the high speed tuning circuit 27 to the signal generator 19 to cause the oscillator to oscillate and transmit via lines 17, a high speed pulse.

The door open low speed signal--since it is the most important--will override any other switch position. The lock open switch, next in importance, will override the perimeter switches.

The command and control station A of FIG. 1, which is the transmit or remote point, is shown in electronic schematic detail in FIG. 2. With reference now to FIG. 2 the 48V direct current voltage from source 12 is applied directly to the telephone lines 16. The 6V direct current voltage from source 14 is used in the circuit as to be described.

A first transformer 60 has its primary winding A connected in series with the one side of the two wire telephone line 16. The secondary or coupling winding B couples the line audio signal pulses to the amplifier 64. The speaker 50 connected to amplifier 64 is that shown in the panel 10 of FIG. 1. The speaker 50 is utilized as a microphone when the push to talk button of the amplifier circuitry is depressed. Also connected, through gate resistor 84, by a tap on to the secondary winding B of transformer 60 is the gate of the SCR 78. The function of SCR 78 is to turn on the red signal warning light 82 (L-1 of FIG. 1A) whenever audio pulses are present on line 16. As explained hereinafter, SCR 78 also turns on the audio oscillator 38 to give an audible warning tone when an audio pulse is received. The gate resistor 84 connected in series with the capacitor 86 and the bleed resistor 88 intensifies the audio signal pulses received via lines 16 and transformer 60.

Transformer 62 and the several windings A, B, C and D are impedance matching transformers to match the impedance of transformer 60 to the audio amplifier 64. Switch 54 is the on-off switch V shown in the panel 10 of FIG. 1. Capacitor 56 is relatively small having the function of passing higher audio frequency signals to the amplifier while enhancing the audio signal pulses tapped by gate resistor 84 to trigger the gate of the SCR 78.

Resistor 90 connected in series with the positive side of the 48 volt direct current source has a voltage drop thereacross indicative of the current flow. This in turn is also related to the state of charge on the storage capacitor 71 in the solenoid circuit of FIG. 3. It is also indicative of an open circuit. The voltage across resistor 90 is applied, through resistor 92, to the gate of transistor 70.

Transistor 70 is a NPN transistor operative to trigger SCR 76 and SCR 78 in the absence of normal standby voltage drop across resistor 90. That is, transistor 70 will conduct when the normal voltage across resistor 90 is applied to its gate. The gates of SCRs 76 and 78 are connected together and to the 6 v direct current voltage source 14 through current limiting resistor 96. These two SCRs have insufficient voltage applied to their gates to cause them to conduct during normal standby. When one of the signal buttons (31 or 33 of FIG. 1) is depressed, the voltage drop across resistor 90 will become smaller than normal. In this way transistor 70 will be less conductive resulting in a larger portion of the positive 6 v direct current being applied to the gates of the SCR 76 and 78. Gate resistor 106 and current limiting resistor 98 supply the conventional circuitry for SCR 76. With sufficient voltage at their gates the SCRs 76 and 78 become conductive and apply a current to pilot light 82 (red indicator). Also the audio oscillator 38 will go into oscillation-- transistors 66, 68, resistor 108, and capacitor 110-- providing an audible tone. Switch 58 provides discretionary silencing of this tone. The above change in condition will occur even though the signal button is depressed only for a moment. It will also occur if there is a malfunction in the loop, cut wires, or loss of power.

Transistor 72 is a NPN transistor operative to trigger into conduction SCR 74 to in turn provide current to pilot light 80 (green indicator). In circuit operation, the resistance in 48 volt direct current closed loop may vary from zero to some amount in the order of 5,000 ohms. Accordingly, potentiometer 100 is adjusted during normal or steady current state to increase the resistance value to that just sufficient to trigger the SCR 74. In this way the green pilot light 80 will light during a recharge cycle--of the storage capacitor in the solenoid actuating circuit-- as the current flow decays to a steady state. The lighted light 80 thusly indicates the closed loop circuit is ready for another operation cycle--the storage capacitor (71 of FIG. 3) in the solenoid circuit is fully charged.

The conventional circuitry for transistor 72 is provided by the gate resistor 94 and the current limiting resistor 102. Similarly resistor 104 is a gate resistor for SCR 74.

Switch 48, also shown as 42 in FIG. 1A, in the 48 v direct current line (telephone line) has as its function to activate the lock solenoid--as hereinafter described. In its normal position the switch 48 provides direct voltage continuity. Upon actuation-- pushed down--switch 48 connects the negative and positive sides of the (telephone) line. Since switch 48 is a spring-type switch it immediately returns to its normal position. When it makes contact again, the negative side of the line to negative, the solenoid actuation circuit is initiated-- also as described hereinafter.

The monitor-locking or local station B of FIG. 1 is shown in electronic schematic detail in FIG. 3. With reference generally to FIG. 1 together with FIG. 3, some mechanical movement is controlled in the local station by an electro/mechanical actuation system. The control power received in the local station B is entirely insufficient to perform the necessary function. Hence, an important aspect of the local station circuitry is to convert the insufficient power to a sufficient power. Since this is in fact accomplished, no local power of any sort is needed or utilized.

Another primary aspect of the local station circuitry is to modify the incoming voltage into an intelligible signal representative of certain mechanical or physical conditions. The modified signals are then returned to the control station--via same cummunications lines--to complete a closed loop.

Still the other most essential aspect of the local station circuitry is to maintain audio communication with the control station.

Referring now specifically to the circuitry shown schematically in FIG. 3, telephone audio communication is maintained by the same two-wire 17A and 17B connected directly to the two-wires 16A and 16B of FIG. 2. There is physically located on the door (11 of FIG. 1) a switch 31 on one side and the switch 33 on the other side. It can be appreciated, of course, that entry may be desired from either side of the door. To initiate the overall function a person desiring entry depresses either switch 31 or 33. These switches are double-pole double-throw and when depressed connect its respective handset 51 or 53 into the circuit and disconnect the other. The switch 31 or 33 upon break and then make further provides a signal that is transmitted via telephone lines to the control station A to establish voice communication. The voice communication does not in any way affect the locking function of the circuit herein described. Voice communication is essential to permit an operator or security guard at the control station A to identify the person requesting entry.

To monitor sound at the door location during standby periods, the switches 31 and 33 interconnect both telephone handsets 51 and 53 in series. This is shown as an alternate connection method FIG. 3. Upon actuation of either switch the other switch will be shunted. It is also characteristic of the circuit that the break and then make of the switch causes a momentary open circuit and an audible pulse to be transmitted both of which illuminates L1 and sounds 38 of FIG. 1A. In this way it becomes a secure system in that cutting of the wires would cause an unanswerable tone at the control station.

A bleeder resistor 55 is connected across both handsets 51 and 53 as a further precaution to cutting of wires, causing operation. This resistor insures that capacitor 83 remains fully charged.

Particular reference is now made to that portion of the circuit of FIG. 3 shown within the dotted line box b. This circuit includes the solenoid 75 for physically moving, when energized a metallic member. The circuit b also includes a voltage accumulating capacitor 71 circuit for providing the necessary power to the solenoid 75. Storage capacitor 71 has its positive side connected directly to the positive side 17a of line 17 and its negative side is connected to the collector of transistor 63 through current limiting resistor 65 and operable to provide sufficient power to energize solenoid 75 a set forth hereinafter.

The solenoid 75 is operable from relay 79. In that the solenoid actuates a two position lock, it must not be permitted to dwell in the energized position which causes a double cycle of unlock and relock. To control the energization period of relay 79 capacitor 83 is included in its circuit. The size of capacitor 83, is relatively small and only sufficient to momentarily actuate the relay 79.

The silicon rectifier 57 is a unilateral current flow component to permit the current to flow out of capacitor 83 to the negative side of the line. This occurs only when the negative and positive side of the line are shorted--as per depressing switch 48 of FIG. 2. As indicated above this is the lock-unlock switch. To continue with the operation of the circuit of FIG. 3--the current flow from capacitor 83 into the negative side of the line discharges capacitor 83.

When the switch (48 of FIG. 2) no longer connects the two lines, that is, when the negative side is again negative, no current will flow from the line to capacitor 83. The line current is blocked by silicon rectifier 57 forcing the current to flow to resistor 61 or to silicon rectifier 69. The discharge of capacitor 83 and the prevention of current flow--upon returning the negative side of the line to negative-- provide the proper activation of relay 79.

Also when the negative side of the line is temporarily positive-- as per above--unilateral current flow silicon rectifier 59 bleeds the negative potential from the gate of PNP transistor 67--thus making it non-conductive. Alternatively when the line returns negative, rectifier 59 blocks current flow to the gate of the transistor 67. In this way transistor 67 becoming non-conductive also provides for the proper discharge of capacitor 83. Also the blocking of the line current prevents the relay 79 coil from seeing a more slowly rising voltage. This is of significance since a sudden burst from capacitor 71 is needed to activate the solenoid 75.

Again upon actuation of the switch 48 (of FIG. 2), it is transistor 63 that initiates the action that ultimately causes the mechanism to lock or unlock. When the switch 48 (of FIG. 1) is in its "down" position--positive side of line to negative--transistors 63 and 67 become non-conductive. As indicated above capacitor 83 is discharged. When the switch returns the lines to its normal position negative current will flow--via gate resistor 61-- to gate of transistor 63 causing it to conduct and the voltage of power storage capacitor 71 to be applied through transistor 63 to the gate of transistor 67 through current limiter resistor 65. This causes transistor 67 to conduct.

Transistor 67 is also a PNP transistor and activates the coil of relay 79 for the brief interval of time required to charge capacitor 83. Its current is also drawn from power storage capacitor 71. It may be pointed out, however, that the total amount of current drawn by these two transistors and relay is negligible when considered in relation to the total amount stored in capacitor 71.

Relay 79 has a swinging contact 73a normally positioned to the left (in the circuit shown) leaving the solenoid 75 circuit open and the storage capacitor 71 circuit closed. When relay 79 is actuated, as above indicated, the contact 73a moves to its opposite position thereby connecting the solenoid 75 in the circuit. This energizes the solenoid 75 which in turn causes the lock to lock or unlock.

The silicon rectifier 69 permits current to flow into power storage capacitor 71, but blocks the reverse flow of current when the line is temporarily connected to positive. The zener diode 77 is a voltage regulator by draining off excess voltage. This gives the system a base operating voltage over wide changes in operating distances or loop resistance.

Particular reference is now made to that portion of the circuit of FIG. 3 that modifies the incoming voltage and retransmits the same as indicative of certain conditions. Transistor 85 together with its attendant circuitry forms an oscillator or pulse signal generator circuit. The tuning circuitry includes the inductance of coil 87, the capacitance of capacitor 97, and the resistances of resistors 95 and 103. The speed of the oscillator, i.e., pulse rate is determined by the amount of gate resistance connecting the junction of resistor 95 and capacitor 97 to the gate of transistor 85. Which resistor is in the circuit is determined by the position of the three or more switches, 41, 43, 105, and/or others in parallel with 105 (of FIG. 3). Switch 43 is in one position or another depending on whether the door is locked or unlocked; whereas switch 41 is in one position or another depending on whether the door is open or closed. Switch or switches 105 are in one position or another depending on the position status of the doors, windows, or other monitored devices. It can be appreciated that the slowest speed is with the lowest resistance.

During normal standby operations, the gate of transistor 85 is open and no oscillations are produced. When the door (11 of FIG. 1) is closed switch 41 is open; but when the door is opened it connects to the gate of transistor 85 and a slow speed pulse is generated. When the locking bolt is in lock position switch 43 is open; but when the bolt is in the unlocked position switch 43 connects resistance 99 to gate of transistor 85. A medium speed pulse is generated. The perimeter switches 105 are normally open; however, if any one of these switches should close the resistance 93 will connect to the gate of oscillator transistor 85. A high speed pulse is thusly generated.

Transformer 87 is a universal output transformer with the audio pulses generated by transistor 85 on the output side of the transformer. Transistor 81 is connected across and thusly triggered by the audio pulses from the secondary of transformer 87. This transistor conducts alternatively with the speed of oscillation and when conducting connects positive and negative sides of the line through capacitor 91. Capacitor 91 is selected to control the power output of the pulses and resistor 89 is a bleed resistor to bleed the voltage across capacitor 91 between pulses. Capacitor 97 alternatively charges and discharges with the speed of oscillation and resistance 95 is a bleed resistor for 97. 07.

Although certain and specific embodiments have been described and illustrated it is to be specifically understood that modifications may be made without departing from the spirit and scope of the invention.