Alarm Apparatus For Facilitating The Detection Of An Unauthorized Removal Of Property

Abstract

An alarm packet of simulated paper currency contains alarm means and alarm-operating circuitry such that, when the packet is removed through an exit irradiated with a local field, the alarm means will thereby be automatically actuated to produce an alarm, as by the release of smoke, tear gas, or staining materials, or by producing alarm sounds, etc. Such a packet is placed with the currency given to a bank robber, and facilitates his apprehension and/or recovery of the loot. The electrical circuitry for actuating the alarm is constructed to prevent operation of the alarm until the packet has been taken into the local field and removed therefrom, so that it will not operate if the robber lingers in the exit area within the field. Preferably the removal of the packet from the local field initiates a timing cycle for further delaying actuation of the alarm means, and provision is made so that if the packet is returned to the local field at the exit before the timing cycle is completed the alarm means will not be actuated and the timing cycle will be reset. The field is preferably an alternating magnetic near-field radiation having a frequency of less than about 3,200 Hz, the preferred frequency range being about 400 to about 1,600 Hz.

Description

BACKGROUND OF THE INVENTION

This invention relates to alarm apparatus for facilitating the detection of an unauthorized removal of property from protected premises, and particularly to improvements in bogus-currency alarm packets useful in deterring bank robbers, in facilitating apprehension of the robber, and in recovering the loot.

Systems are known in the prior art which utilize alarm means associated with property subject to unauthorized removal in such manner that if the property is removed without authorization the alarm means will automatically operate to produce a visual and/or audible alarm, such as smoke, tear gas, or explosions which will not only draw attention to the person making the unauthorized removal, but also will facilitate his capture or frighten him so that he may abandon the loot. The alarm means may also produce a marking or staining of the loot or the unauthorized remover or his clothing, and thus further aid in apprehension of the unauthorized remover and in recovery of the loot.

While not limited thereto, the invention will be described with particular reference to the robbery of paper currency from a building such as a bank. For example, in U.S. Pat. No. 3,424,122 of S. M. DeAngelis, issued Jan. 28, 1969, it has been proposed to provide at the storage location for the currency, such as in a bank teller's drawer, a packet of bogus paper currency having hidden within it alarm means such as a body of explosible smoke powder, a delay fuse, and an electrical ignition device for the fuse. In the event of a robbery, the packet is given to the robber along with the real currency. When the bogus packet is given to the robber, the alarm means therein is manually or automatically actuated to start burning of the delay fuse, and at a predetermined time thereafter the charge of material explodes, releasing smoke, detonating explosives, or producting loud audible sounds, for example.

One difficulty with such an arrangement is that the delay time is normally fixed with respect to the time of giving the packet to the robber, while there is no way of anticipating the timing involved in his escape procedure. Accordingly, if the delay fuse is set for a short time the robber may still be within the bank lobby when the packet explodes, in which case (particularly if tear gas is released) there is a possibility of affecting innocent persons by the packet and, furthermore, the robber may thereby be incited to take action dangerous to persons within the bank or in its vicinity.

The above-cited U.S. Pat. No. 3,424,122 also proposes that the delay time may be initiated not by the giving of the package to the robber, but by his passage through an exit irradiated with a local field which operates an electrical receiver within the packet to start the burning of a relatively slow delay fuse. The theory in this case is that the packet then will not explode until the robber reaches the exit, and even then only after a short delay during which he likely will be moving well away from the bank exit, and perhaps in an automobile or other escape vehicle.

U.S. Pat. No. 3,564,525 to H. J. Robeson et al., issued Feb. 16, 1971, discloses in more detail one particular manner of constructing electronic circuitry and alarm means secreted in a packet of bogus paper currency and activated through reception of a local field which irradiates the exit from the bank. The circuitry disclosed therein utilizes silicon controlled rectifiers, one of which is turned on by the removal of the packet to the local field and thereafter remains turned on to charge a timing capacitor until, after a predetermined time interval, the other silicon controlled rectifier is turned on to accomplish ignition of a disabling charge, such as tear gas and smoke.

The latter system has the drawback that, should the robber decide to remain, in, or perhaps return to, the area near the exit at which the local field is produced, ignition may occur while he is in this position, and again persons in or around the bank premises may be greatly upset either by the charge or by the reactions of the robber to the functioning of the device.

It is also desirable that the field reaching the packet be reduced as little as possible by surrounding metal so that if the robber places the packet in a metal container the shielding thereby produced will not prevent proper operation of the system. If the shielding effect is strong, not only will more transmitted power be needed but some additional means for localizing the field will generally be necessary.

Accordingly, it is the object of the invention to provide new and useful alarm apparatus adapted to be removed during unauthorized removal of property and thereafter to provide an automatic alarm.

Another object is to provide such apparatus of a type which can be actuated only after the alarm apparatus has been moved to a point within a local field in the exit path of the person making the unauthorized removal, and will not be actuated so long as the person remains within the field or departs from it but returns within a prescribed time interval.

Another object is to provide apparatus of the last described type which is small, simple, reliable and inexpensive.

A further object is to provide a system using such apparatus in which the degree of shielding of the packet from the radiated field when the packet is placed in a metal container is reduced.

SUMMARY OF THE INVENTION

These and other objects of the invention are achieved by the provision of an improvement in apparatus for use in protecting against unauthorized removal of property from an area by way of a path extending through a localized field, which apparatus is adapted to be associated with said property so as to be removed from the area along with the property during unauthorized removal of the property and comprises an electrical alarm system responsive to the removal of the apparatus from the area through the field to produce an alarm. According to the improvement of the invention, said alarm system comprises means for preventing occurrence of the alarm until said apparatus has entered and then been removed from said local field, and means responsive to said removal from said field to enable said alarm. Since the alarm is not enabled until the apparatus has been removed from the field, there is no danger of alarm activation if the unauthorized remover should remain in the area of the exit, as he may do in awaiting an especially propitious time for an escape or in waiting for confederates or for an escape vehicle for example, etc. Accordingly, innocent persons in the vicinity of the exit will not be affected by operation of the alarm means or the reaction of the unauthorized person to the alarm.

Preferably, the removal of the apparatus from the field initiates a timing interval, so that the operation of the alarm is delayed for a predetermined time interval even after removal of the apparatus from the field, so that the alarm will not occur in the immediate vicinity of the exit.

In this event, the invention preferably also comprises means responsive to return of the apparatus to a position within the local field prior to the end of the time interval for preventing an occurrence of the alarm until the apparatus has again been removed from the field for longer than said time interval. Utilizing this feature of the invention, if the unauthorized person should leave the exit area briefly and then return to it, there would still be no danger of an actuation of the alarm while he remains at the exit nor until a predetermined interval has elapsed after he again leaves the exit area. Preferably also the field comprises an alternating magnetic near-field radiation having a frequency less than about 3,200 Hz, the preferred range being from about 400 to about 1,600Hz. This type of field has been found to be substantially less attenuated by metal containers, particularly ferromagnetic metal containers, in which the robber may place the packet at the start of his escape. In a preferred form, the invention comprises an alarm packet of simulated paper currency containing suitable alarm means and alarm actuating circuitry, the alarm-actuating circuitry responding to a local field irradiating an exit in the path of escape of a robber; the latter circuitry includes receiver means which responds to the local field to produce an input signal level sufficient to turn on a storage device, such as silicon control rectifier. Means are included which sense the simultaneous occurrence of the "on" state of the storage device and the absence of the input signal due to the local field, and produce an output signal which indicates that the packet has not only entered the field but has later left the field. The latter output signal can be used to operate the alarm immediately, but preferably instead initiates a timing cycle of predetermined duration after which the alarm means is automatically actuated. Also in the preferred form, the circuitry is so arranged that the received signal produced when the apparatus is returned into the local field terminates the timing cycle and causes the apparatus to revert to the condition it was in when the apparatus was first brought within the local field, thus preventing actuation of the alarm means until it has again been removed from the field for a time greater than the timing interval. Other features of the preferred embodiment of the invention include specific circuit arrangements for accomplishing the above-described functions in particularly advantageous ways.

BRIEF DESCRIPTION OF DRAWINGS

These and other objects and features of the invention will be more readily understood from a consideration of the following detailed description, taken in connection with the accompanying drawings, in which:

FIG. 1 is a schematic plan view of bank premises and the immediate vicinity thereof, at which the apparatus of the invention may be used;

FIG. 1a is a fragmentary schematic elevational view as viewed along lines 1a -- 1a of FIG. 1, showing the exit from the premises illustrated in FIG. 1;

FIG. 2 is a plan view, with parts broken away, of a dummy packet of paper currency containing alarm means constructed in accordance with the invention, and FIG. 2a is a side-elevational view thereof with parts broken away;

FIG. 3 is a block diagram of the alarm device of the invention; and

FIG. 4 is an electrical schematic of one preferred embodiment for the electrical circuit of the alarm device of the invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Referring now to the particular embodiment of the invention shown by way of example only in the accompanying drawings, FIGS. 1 and 1a illustrate bank premises comprising the bank walls 10 and the cashiers' counter 12, defining between them the bank lobby 14. The bank exit 16 comprises a pair of recessed doors 18 defining an alcove 20 opening upon the sidewalk 22 adjacent the street 24 upon which there is shown a vehicle 26, which may for example be a get-away car for bank robbers.

The cashiers' windows 30, 32, and 34 are shown at the cashiers' counter, behind which are normally stationed respective cashiers 36, 38 and 40. At each cashier's station there will normally be a cash drawer containing paper currency in banded packets.

A source 46 of radiation is positioned adjacent the exit 16 so as to produce a local radiation field, selectively in the immediate area of the exit, as indicated by the dotted volume 48. Preferred for this purpose are radiations producing a magnetic field, an electric field, or a combination of both, any of these being designated herein as an electromagnetic field. In the preferred embodiment, source 46 produces relatively low-frequency, near-field magnetic radiations, which are readily localized so that their principal effects are confined substantially to the volume 48 near the exit 16. Such apparatus is well known in the art and need not be described in detail herein.

Referring now to FIGS. 2 and 2a which show in detail a type of bogus-currency packet to which the invention is applicable, the packet of currency 50 is surrounded and held by the usual band 52, and typically only one or a few bills near the top and bottom of the packet are genuine, while those in the center may be bogus. A recess 54 formed within the packet of bogus bills contains an alarm device. In this example the device comprises a printed-circuit board 56 to which alarm means 58 are secured by means of suitable lacing tape 60, and which when actuated is effective to release smoke, stain, tear gas, explosives, or any combination thereof. Also mounted on the printed-circuit board are the electrical alarm-actuating means comprising electrical circuit elements embedded in a plastic block 62, plus the battery 64, the resistor 66 and the capacitor 68 which for convenience are separately mounted upon the circuit board in this embodiment.

The packet 50 normally is located in a cashier's drawer, the top inner surface of which drawer is represented at 69, the packet normally being positioned upon a magnetic keeper assembly 70 secured to the drawer surface 69. The latter assembly cooperates with the magnetically actuatable reed switch 71 within the packet to maintain the alarm-actuating means in a safe de-actuated state while in position upon the magnetic keeper assembly. In this example, the latter assembly comprises a plastic tray 72 having raised rim portions at and adjacent each corner to aid in positioning the packet thereon. The tray has a false bottom 73 below which extend a pair of transverse ribs 74, 75 defining a central transverse packet for receiving a magnet 76 having opposite magnetic poles at its upper and lower surfaces. A steel plate 78 glued to the magnet and the underside of the tray closes the bottom of the tray and holds the magnet in place. When the packet 50 is in position on the magnetic keeper assembly as illustrated in FIG. 2a, the magnetic field produced by the magnet 76 holds the reed switch 71 in its open state to prevent the application of supply voltage to the alarm actuating circuit, as will be described more fully hereinafter.

Referring again to FIG. 1, should a robber cause the removal of currency from any of the cashier's stations, it is arranged that the packet 50 will be among the packets of currency taken; for example, if the cashier is asked by the robber to fill a container with packets of currency, the cashier will place one of the dummy packets in the container along with the genuine currency. As soon as the packet 50 is thus removed from the magnet keeper assembly, the reed switch 71 closes, so that the electrical alarm-actuating circuit is enabled.

The packet of the invention is so made that the long as the robber remains within the bank lobby 14 and does not enter the irradiated volume 48 adjacent the exit 16, no further change will occur in the electrical conditions within the packet. However, when in the course of his escape he enters the irradiated volume 48, the circuitry within the packet is thereby automatically "primed" or "set," but it is not triggered until he leaves the irradiated volume 48; thus, so long as he remains within the volume 48 adjacent the bank exit, there is no danger of premature ignition of the alarm means. further, in the preferred embodiment of the invention the removal of the packet from the irradiated volume 48 does not produce immediate ignition of the alarm means, but rather initiates a timing cycle at the end of which such ignition occurs. Further in accordance with a preferred feature of the invention, the electrical circuitry is such that, should the robber return with the packet to the irradiated volume 48 after having once left the latter volume, and if he does so within the time interval of the timing cycle, actuation of the alarm will be prevented and the circuitry returned to its primed or set state, and so long as he again remains within the irradiated volume 48 ignition will not occur. Accordingly, actuation of the alarm means will occur only after the robber has removed the packet into the irradiated volume 48, has removed if from the volume 48, and has been absent from the latter irradiated volume for a time greater than the duration of the timing cycle. The latter timing cycle is preferably provided with a duration such that the robber will normally be well away from the exit area when the alarm means is ignited, thereby avoiding or minimizing danger to innocent persons in or around the bank premises.

Referring now to FIG. 3 which shows in broad outlines an arrangement in accordance with the invention, the electronic circuitry contained within the packet 50 comprises a receiver 80 including a pickup circuit 82 which picks up, or senses, the radiations from source 46; an amplifier 84 for amplifying the signals from pickup circuit 82; and the rectifier and filter circuit 86 for producing a substantial DC output voltage only when the pickup circuit 82 is within the irradiated region 48, and for discriminating against interfering radiations. Suitable receiver means for such purposes are well known in the art, and one preferred form thereof will be described in detail in connection with FIG. 4.

The output of the rectifier and filter circuit 86 is supplied to a storage circuit 88, the output of which is supplied to input terminal 90a of simultaneity circuit 90; the output of circuit 86 is also supplied directly to input terminal 90b of circuit 90. When, and only when, simultaneity circuit 90 is supplied with signal at its input terminal 90a but not at its input terminal 90b, it causes the initiation of a cycle of the timing circuit 92 to which its output is supplied, and after the latter timing circuit 92 has operated for a predetermined interval, the alarm means 94 will be actuated. Storage circuit 88 is set or primed by the output signal produced by rectifier and filter circuit 86 when the packet is moved within the irradiated volume 48, and remains in its set condition thereafter. It therefore thereafter continues to supply signal to input 90a of the simultaneity circuit 90. Input to the other input terminal 90b of the latter circuit is present only when the packet is later moved outside of the volume 48, and accordingly simultaneity circuit 90 is operated only when the packet has been moved into the irradiated volume 48 to operate storage circuit 88 and thereafter removed from volume 48 so that the output from rectifier and filter circuit 86 has disappeared.

Should the output from the rectifier and filter circuit 86 later reappear, as will occur if the packet is again brought into the irradiated volume 48, the simultaneity circuit 90 will be actuated again to terminate the timing cycle and to reset the cycle to its initial condition. Accordingly, the packet must have been removed from the irradiated volume 48 for a time greater than the timing cycle duration in order for the alarm means 94 to be actuated.

Referring now to the exemplary embodiment of the invention shown in detail in FIG. 4, in which parts corresponding to those of the earlier Figures are indicated by corresponding numerals, the battery 64 is connected between a low-potential line 100 and a high-potential line 102 which is positive with respect to the low-potential line. The reed switch 71 is connected in series in the high-potential line, and is normally open, as shown, when the packet is positioned on the magnet keeper assembly. When the packet is removed therefrom, the reed switch 71 is closed so as to supply the positive potential on line 102 to the various elements of the circuit.

Coils 106 and 108 represent pickup coils for sensing periodically varying electromagnetic radiations from source 46, the capacitor 110 connected across the series arrangement of coils 106 and 108 serving as a tuning capacitor to tune the circuit to the frequency of alternation of the electromagnetic radiations. In one specific embodiment, the source 46 may produce near-field magnetic signals of 1,600 c.p.s. frequency, in which case the inductance of each of the coils 106 and 108 may be about 350 millihenries, and capacitor 110 may have a value of about 0.01 microfarad. The coils 106 and 108 are preferably aligned at right angles to each other to minimize the effect of the orientation of the packet with respect to the source 46.

The output from the series combination of coils 106 and 108 is applied between the inverting terminal 2 and the non-inverting terminal 3 of the differential input operational amplifier 114, by way of a small current-limiting resistor 116, which may for example have a value of 1,000 ohms. The feedback resistor 120 is connected between the output terminal 6 of amplifier 114 and the inverting input terminal 2 thereof in the usual manner; terminal 7 thereof is connected directly to the high-potential line 102; and terminal 4 thereof is connected to the low-potential line 100. Typically, amplifier 114 provides a gain of about 200, for which purpose a value of resistor 120 of about 200,000 ohms is suitable.

Bias for the input terminals of the amplifier 114 is provided by the voltage divider made up of resistors 126 and 128, the tap point 130 of which is connected through resistor 116 to the inverting terminal 2 of the amplifier. A suitable value for resistors 126 and 128 is 2,200 ohms each, where the voltage of the battery source 64 is assumed to be about 126 volts.

The output from terminal 6 of operational amplifier 114 is supplied by way of series resistor 140 (typical value 10,000 ohms) and capacitor 142 (typical value 0.01 microfarad) to input terminal 2 of operational amplifier 146. Bias for terminal 3 of amplifier 146 is supplied from the tap point between resistors 150 and 152 connected as a voltage divider between the high and low-potential lines 100 and 102. Suitable values of the divider resistors are 2,200 ohms each. Terminal 7 of amplifier 146 is connected to the high-potential line 102 and terminal 4 to the low-potential line 100.

The output terminal 6 of amplifier 146 is connected to the input thereof by means of a feedback circuit comprising resistor 160 (typical value 200,000 ohms) connected directly to input terminal 2; capacitor 162 (typical value 0.01 microfarad) connected to the junction point 164 between resistor 140 and capacitor 142; and a further resistor 165 (typical value 536 ohms) connected between junction point 164 and input terminal 3 of the amplifier. The amplifier 146 and its associated circuitry operate as an amplifier tuned to the input signal frequency, in this case assumed to be about 1600 cycles per second.

The alternating output at output terminal 6 of amplifier 146 is then supplied to a circuit for deriving a DC voltage proportional to the amplitude of the alternating signal. Thus the signal at output terminal 6 of amplifier 146 is passed through capacitor 167 to junction point 168, which in turn is connected to the cathode of a diode rectifier 170, the anode of which is connected directly to the low-potential line 100, whereby negative half-cycles of the alternating signal are effectively clipped or removed. A typical value for capacitor 167 is 0.01 microfarad. Junction point 168 is also connected to the anode of diode rectifier 172, the cathode of which is connected to the resistive divider, made up of resistors 174 and 176, extending to the low-potential line 100. Typical values for resistors 174 and 176 are 33,000 ohms and 330,000 ohms respectively. The junction point 178 between resistors 174 and 176 is connected to the base of an NPN transistor device 180 and to capacitor 182, the other terminal of which capacitor is connected to the low-potential line 100. Capacitor 182 may typically have a value of about 4.7 microfarad.

Diode 172 passes the positive half-cycles of the alternating signals supplied thereto, while blocking negative half-cycles, and the combination of resistors 174 and 176 with capacitor 182 not only supplies appropriate operating bias for transistor device 180 but also provides a charging and discharging time constant for capacitor 182 appropriate for discriminating against certain types of spurious interfering signals having frequencies substantially different from the frequency of the signal from source 46.

While transistor device 180 is shown in the form of an ordinary transistor, which in some cases it may be, it is preferably a Darlington-type integrated circuit device providing greater isolation between input and output terminals thereof. The bias applied to transistor device 180 by the previously-described circuit is such as normally to maintain the latter device in a non-conductive state in the absence of received signals, but to change it to a highly-conductive state when signal is received from source 46 in greater than a predetermined minimum strength. The collector of transistor device 180 is connected directly to the high-potential line 102, and the emitter thereof is connected directly to the low-potential line 100 by way of an emitter load resistor 186. Accordingly, when the packet containing the circuit is moved into the irradiated volume 48, a substantial voltage is produced across emitter load resistor 186, and when the packet and circuitry is outside the irradiated volume 48, the voltage across resistor 186 is near zero. A suitable value for resistor 186 is 1,500 ohms.

The memory function is in this case provided by the silicon controlled rectifier (SCR) 190 and associated circuitry. The cathode turning the SCR 190 is connected directly to the low-potential line 100, and the anode thereof is connected through comprising 192, typically normally 1,500 ohm value, to the high-potential line 102. The gate electrode of the SCR is connected by way of isolating resistor 198 to the emitter of transistor device 180. When the voltage across emitter resistor 186 is near zero, SCR 190 is non-conductive. In the presence of a received signal, the increase signal voltage across the resistor 186 is sufficient to trigger SCR 190 and place it in its conductive condition; due to the inherent characteristics of silicon controlled rectifiers, it remains in its highly conductive state thereafter even though the voltage across resistor 186 may disappear entirely. SCR 190 therefore serves as a memory device for remembering the fact that signal has been received, i.e., that the packet has once been introduced into the irradiated volume 48.

The simultaneity circuit function is provided by the parallel combination of the NPN transistors 200 and 202, the emitters of which are connected directly together and to the low-potential line 100, and the collectors of which are connected directly together and through common load resistor 206 to the high-potential line 102. The base of transistor 200 is connected to the junction point 210 between the divider resistors 212 and 214, the latter divider being connected between the anode of the SCR 190 and the low-potential line 100. The bias voltage thereby applied to the base of transistor 200 is such that, when SCR 190 is not conducting, transistor 200 is in a high-conduction state, and when SCR 190 is rendered conductive, transistor 200 is cut off, or placed in a non-conductive state.

Transistor 202, on the other hand, is in its normally off, or non-conductive state, in the absence of received signal, by virtue of the connection of its base to the emitter of transistor device 180 by way of isolation resistor 206, the voltage at the emitter of transistor device 180 at such times being about zero. When a signal is received and the voltage across resistor 186 becomes more positive, transistor 202 is turned on, or placed in a highly-conductive state.

Typical values for the resistors just described are 1,500 ohms for resistor 198, 4,300 ohms for each of resistors 212 and 214, 33,000 ohms for resistor 206 and 33,000 ohms for resistor 216.

It will therefore be appreciated that the combination of transistors 200 and 202 is highly conductive before any signal is received, because transistor 200 is normally on; that it is highly coductive whenever the packet of bogus currency is within the irradiated volume 48, since transistor 202 is then highly conductive; and that once the packet has entered the irradiated volume and has subsequently been removed therefrom, the combination of transistors 200 and 202 is non-conductive, since SCR 190 remains conductive to hold transistor 200 turned off at all times, and there is then no voltage across emitter resistor 186 to hold transistor 202 on.

A capacitor 220, which may have a value of about 3.3 microfarads, is preferably provided between the low-potential line 100 and the section of high-potential line 102 beyond the reed switch 71, to smooth out, or reduce the effects of, large transients in the supply voltage, such as may be produced for example by the closing or opening of the reed switch 71, and which might cause false turn-on of SCR 190.

The collectors of the parallel connected resistors 200 and 202 are connected to a timing circuit comprising resistor 224 and capacitor 226, cooperating with the timing-start diode rectifier 228. More particularly, resistor 224 and capacitor 226 are connected in series between the high-potential line 102 and the low-potential line 100 so that, absent any diverting or parallel current paths, capacitor 226 will be charged through resistor 224 from zero toward the supply voltage when reed switch 71 is closed. However, diode rectifier 228 has its cathode connected to the collectors of transistors 200 and 202 and its anode connected to the tap point 230 between resistor 224 and capacitor 226 to provide a controllable current-diverting path from tap point 230 to the low-potential line 100 by way of the paralleled transistors 200 and 202. Thus when either of the transistors 200 or 202 is in its high-conduction state, the cathode of diode rectifier 228 will be held near the low supply potential of line 100 and capacitor 226 will be prevented from charging substantially above the latter potential. It is only when both of transistors 200 and 202 are non-conductive, i.e., when SCR 190 has been turned on and transistor 184 is non-conductive because no adequate signal is being received from source 46, that diode rectifier 228 will be blocked and capacitor 226 permitted to charge toward the high supply potential. Furthermore, even if charging of capacitor 226 has begun, should signal again be received from source 46 so as to turn on transistor 202, diode rectifier 228 will again become conductive and capacitor 226 discharged to its original state.

In one example in which a 20-second timing cycle was desired, the value of resistor 224 was about 560,000 ohms and of capacitor 226 was about 22 microfarad.

Tap point 230 is connected to the emitter of the unijunction transistor 250, one base of which is connected through resistor 252 to the high-potential line 102, and the other base of which is connected through resistor 254 to the low-potential line 100. In one particular application in which the unijunction was of the type 2N4870, resistor 252 had a value of 470 ohms and resistor 254 had a value of about 37 ohms. When the voltage at tap point 230 (i.e., at the emitter of unijunction transistor 250) is zero, the unijunction transistor is non-conductive, but when the latter voltage rises to a predetermined threshold level, the unijunction transistor becomes strongly conductive so as to produce a substantial output voltage across its output base resistor 254. Since it requires a predetermined time interval for the voltage at junction 230 to rise to this threshold level, unijunction 25 does not become conductive until the end of a predetermined timing interval following the time at which both transistors 200 and 202 become non-conductive. The voltage developed across resistor 254 when unijunction transistor 250 thus becomes conductive is supplied to the gate of another SCR 260, the cathode of which is directly connected to the low-potential line 100 and the anode of which is connected through resistor 262 to the high-potential line 102. In a typical application, resistor 262 may have a value of about 470 ohms. The high-potential line 102 is connected to an output terminal 266, and the anode of SCR 260 is connected to another output terminal 268, between which two output terminals there is connected the electric match 270, normally physically located in the alarm means 58 of FIG. 2.

SCR 260 is normally non-conductive, but responds to the voltage developed across resistor 254 when unijunction transistor 250 becomes conductive to itself become highly conductive and to remain so thereafter, the resultant conduction through electric match 270 causing the above-mentioned ignition.

In the overall operation of the circuit, when the bogus-currency packet is removed from the magnet keeper assembly, the reed switch 71 automatically closes, thus supplying operating supply potential to the entire circuit. When the packet is still in the lobby area 14 and remote from the irradiated volume 48, transistor device 180, SCR 190, unijunction transistor 250 and SCR 260 are all substantially non-conductive. Also under these conditions, transistor 200 is conductive and renders diode rectifiers 228 conductive, so that timing capacitor 226 is prevented from charging. When a signal is received by one or both of the pickup coils 106, 108 from source 46, i.e., when the packet has been moved into the irradiated volum 48 during the escape of the robber carrying the packet, the resultant signal is amplified, rectified and used to turn on transistor device 180, as a result of which SCR 190 is turned on permanently, transistor 200 is turned off permanently, and transistor 202 is turned on temporarily while the received signal is present. Under these conditions, the timing capacitor 226 still cannot charge. However, as soon as the packet is thereafter removed from the irradiated volume 48, as by the robber leaving the premises by way of the exit and proceeding upon the adjacent sidewalk, transistor 202 also becomes non-conductive and capacitor 226 begins to charge through resistor 224. When the voltage across capacitor 226 reaches a predetermined threshold level, which will occur following a predetermined time interval, unijunction transistor 250 becomes conductive and SCR 260 is turned on permanently so as to operate the electric match 270 and cause the ignition and alarm actuation.

However, if after the packet has been removed from the irradiated volume 48, and capacitor 226 has begun to charge but has not yet reached the threshold level necessary to turn on unijunction transistor 250, the packet is returned to the irradiated region (as may occur should the robber return to the vicinity of the exit 16 while waiting for a pickup car or while seeking to avoid nearby police), transistor 202 will again be turned on immediately to discharge capacitor 226 and to hold it discharged until the robber and packet again leave the irradiated volume, at which time the timing cycle will again become initiated. It is only when the packet has been moved into the irradiated volume, removed therefrom, and maintained away from the irradiated volume for a predetermined timing interval, that ignition of the alarm means can occur. Accordingly, the chances of alarming innocent persons in the bank or in the vicinity of the exit therefrom are substantially minimized, while providing that the alarm will occur at a somewhat later time.

As a preferred feature of the invention, the radiations from transmitter 46 comprise alternating near-field magnetic radiations of a frequency less than about 3,200 Hz and preferably about 400 to 1,600 Hz, and the packet receiver is designed to operate at the frequency selected. By "near-field" is meant the field existing within a distance small compared with the wavelength of the radiations. It has been found that if the robber places the packet in a relatively thick-walled ferromagnetic container such as a steel tool box of 0.036 inch wall thickness, the strength of the field reaching the packet is greatly reduced, for example by a factor of nearly 10 when the frequency is about 8,000 Hz. Using a frequency of 800 Hz this attenuation caused by electrical shielding is less than one-half that occurring at 8,000 Hz. If the frequency is further lowered the attentuation decreases even further. However, at very low frequencies interference from power-line radiations and the like becomes more of a problem, and a preferred practical value is in the range of from about 400 to 1,600 Hz, although useful improvement over the results obtained at 8,000 Hz can be obtained up to about 3,200 Hz.

It will be appreciated that if one attempts to make up for the attenuation produced by a shielding enclosure or container by merely increasing the transmitter power to the level for which the packet will be actuated even when in the container, then the region in which the packet will become actuated when not in a container will extend farther from the transmitter, for example to the stored position of the packet at the cashier's location. Under these conditions the packet would be undesirably "primed" as soon as it was lifted from its tray.

This feature of the invention is useful and advantageous as an improvement even in prior-art types of system not using the above-described inventive circuitry, for preventing actuation of the packet until the packet has first entered and then been removed from the field.

The invention may be utilized in protecting premises other than banks and for protecting against removal of property other than currency or money and if desired may be utilized to operate a remote alarm by turning on a transmitter within the packet, rather than by operating an alarm which is contained within the packet.

Thus although the invention has been described in the interest of complete definiteness with particular reference to specific embodiments thereof, it will be understood that it may be embodied in a variety of forms diverse from those specifically shown and described, without departing from the scope and spirit of the invention as defined by the appended claims.

Claims

What is claimed is:

1. In an alarm packet useful in impeding the successful robbery of paper currency from a bank having an exit irradiated with a local alternating electromagnetic field, said packet comprising a packet of simulated paper currency; electrically operable alarm means concealed within said packet and responsive to an electrical alarm signal to produce an alarm; and an alarm-signal generating circuit concealed within said packet for operating said alarm means; the improvement wherein said alarm-signal generating circuit comprises:

receiver means for receiving, amplifying and rectifying said local alternating magnetic field to produce a direct-voltage input signal of greater than a first level only when said packet is within said field, a first SCR, a direct-voltage supply source for supplying anode-to-cathode voltage for said first SCR, means normally biasing the gate electrode of said first SCR at a level for which said SCR is non-conductive, means supplying said gate electrode with said input signal to render said SCR conductive when said input voltage exceeds said first level, a timing resistor and a timing capacitor connected in series across said supply source, timing-cycle start means connected in parallel with said capacitor and normally conductive to prevent said capacitor from charging to a predetermined voltage level, means responsive to the simultaneous occurrence of said conductive state in said SCR and to the absence of said first level of said input signal for reducing the conductivity of said timing-cycle start means sufficiently to allow said capacitor to charge to said predetermined voltage level, and threshold means responsive to the occurrence of said predetermined voltage level across said capacitor to actuate said alarm means, said timing-cycle start means being responsive to the presence of said level of said input signal to resume its conductive state and discharge said timing capacitor.

2. The alarm packet of claim 1, in which said timing-cycle start means comprises a normally on transistor and a normally off transistor in parallel with each other, a load element connecting said parallel combination across said supply source, means connecting the control electrode of said normally on transistor with said SCR to turn off said normally on transistor when SCR is turned on, means for supplying the control electrode of said normally off transistor with said input signal, and unilaterally conductive means connecting said parallel combination to said timing capacitor in the polarity to be blocked when both of said transistors are in their off condition.

3. The alarm packet of claim 2, in which said alarm means comprises an electric match and a heat-releasable material adjacent said electric match, whereby when current is passed through said electric match said material is released to the exterior of said packet.

4. In apparatus for use in protecting against unauthorized removal of property from an area along a path extending through a localized field, said apparatus being adapted to be associated with said property so as to be removed from said area along with said property during an unauthorized removal thereof, said apparatus comprising an electrical alarm system responsive to removal of said apparatus from said area through said localized field to produce an alarm, said alarm system comprising means for preventing occurrence of said alarm until said apparatus has entered and then been removed from said localized field, means responsive to said removal from said field to enable said alarm, and means for delaying the occurrence of said alarm for a predetermined time interval after said removal from said field, the improvement comprising:

means responsive to return of said apparatus to a position within said localized field prior to the end of said time interval for preventing the occurrence of said alarm until said apparatus has again been removed from said field for longer than said time interval.

5. Apparatus in accordance with claim 4, in which said alarm apparatus comprises a packet of simulated paper currency and said alarm system is concealed within said packet.

6. In combination with the apparatus of claim 5, means for producing said localized detection field adjacent an exit from said area, said area comprising the public area of a bank.

7. In a robbery-protection alarm device adapted to be energized by the action thereon of an electrically produced local field located at an exit from the protected premises, and comprising a dummy packet of paper currency having secreted therein electrically-actuatable alarm means and electrical alarm-actuating means, the improvement wherein said alarm-actuating means comprises:

first means for sensing the presence of said alarm device in said local field and for producing a first output signal indicative thereof;

signal storage means having a normal deactuated state and an actuated state, and responsive to said first output signal to assume said actuated state and to remain in said actuated state after said first output signal disappears due to removal of said device from said field;

means responsive to said first output signal and to the state of said signal storage means for producing a second output signal only when said signal storage means is in said actuated state and said first output signal is simultaneously absent;

means responsive to said second output signal for operating said alarm means;

said signal storage means comprising a solid-state controlled rectifier having a control electrode supplied with said first output signal for turbing on said controlled rectifier when said first output signal occurs, said means for producing a second output signal co mprising a first nor mally on transistor and a second normally off transistor having their emitter-collector current paths in parallel with each other, means for maintaining said first transistor in its off state when said controlled rectifier is in its on state, and means for maintaining said second transistor in its on state only when said first output sitnal is present, whereby the parallel combination of said first and second transistor becomes non-conductive to produce said second output signal only after said first output signal has appeared and then disappeared;

said means for operating said alarm means comprising a timing circuit supplied with said second output signal to initiate a timing cycle for delaying operation of said alarm means for a predetermined interval of time following the occurrence of said second output signal;

said timing circuit comprising a timing capacitor effectively in parallel with said parallel combination of said first and second transistors so as to charge when said parallel combination is non-conductive and when said alarm device is returned to a position within said field said timing capacitor is discharged through said parallel combination and said timing circuit thereby reset.