US3587484A - Security container - Google Patents

Abstract

A PORTABLE SECURITY CONTAINER IS PROVIDED, AT A WALL THEREOF, WITH A GUARD CIRCUIT COMPRISING AN ELECTRICALLY CONTINUOUS ELONGATED CONVOLUTED CONDUCTOR, AND AT LEAST ONE OPEN CIRCUITED ELONGATED CONVOLUTED OR BRANCHED CONDUCTOR CLOSELY PROXIMATE THE CONTINUOUS CONDUCTOR BUT INSULATED THEREFROM, A FURTHER CIRCUIT WHICH CAN TAKE MORE THAN ONE STATE BEING ADAPTED TO CHANGE STATE IN RESPONSE TO A CHANGE IN THE RESISTANCE OF THE CONTINUOUS CONDUCTOR, OR TO CHANGE STATE IF CONTINUITY IS ESTABLISHED BETWEEN AN OPEN CIRCUITED CONDUCTOR AND THE CONTINUOUS CONDUCTOR, FOR EXAMPLE IF AN ATTEMPT IS MADE TO PENETRATE THE WALL.

Description

United States Patent [72] lnventor Edward A. Munton Thorpe Bay, Essex, England [21] Appl. No. 841,877 [22] Filed July 15,1969 [451 Patented June 28, 1971 [731 Assignee Vigil Security Limited 1 Brighton, England [32] Priority July 18, 1968 [3 3] Great Britain [31 34282/68 [54] SECURITY CONTAINER 13 Claims, 7 Drawing Figs.

[52] US. Cl 109/25, 317/134 [51] 1nt.C1 ..G08b 15/02 [50] Field of Search 109/25, 44, 29, 42, 36; 317/134; 340/164, 280, 276; 70/278 [56] References Cited UNITED STATES PATENTS 1,606,516 11/1926 Daly 109/25 2,436,809 3/1948 Joel 70/278 3,056,125 9/1962 Harry 109/44X 3,234,516 2/1966 Mitler 70/278X 3,321,673 5/1967 Wolfe 70/278X 3,392,558 7/1968 Hedin et al. 3l7/134X Primary Examiner-4. Karl Bell Attorney-Cushman, Darby & Cushman ABSTRACT: A portable security container is provided, at a wall thereof, with a guard circuit comprising an electrically continuous elongated convoluted conductor, and at least one open circuited elongated convoluted or branched conductor closely proximate the continuous conductor but insulated therefrom, a further circuit which can take more than one state being adapted to change state in response to a change in the resistance of the continuous conductor, or to change state if continuity is established between an open circuited conductor and the continuous conductor, for example if an attempt is made to penetrate the wall.

PATENTEU JUH28 1971 SHEET 1 [1F 5 lnucnlor Attorney c PATENTED auwzwi v3587.484 sum 2 OF 5 A ttarneys PATENTED JUN28 I971 SHEET 5 BF 5 SECURITY CONTAINER This invention relates to a security container.

In one aspect, although'not so restricted, the invention provides a security container or a structure adapted to form part thereof provided at a wall thereof, with a guard circuit comprising an electrically continuous elongated convoluted conductor, and at least one open circuited elongated convoluted or branched conductor closely proximate the continuous conductor but insulated therefrom, a further circuit which can take more than one state being adapted to change state. in response to a change in the resistance of the continuous conductor, or to change state if continuity is established between an open circuit conductor and the continuous conductor.

The conductors may be arranged in two layers, coextensive with each other and with the wall, the continuous conductor and at least one said open circuited conductor being provided in each layer.

The continuous conductor may have a plurality of spaced apart portions, the at least one open circuited conductor also having a plurality of spaced apart portions, each portion ofthe electrically continuous conductor being interposed in a respective space between neighboring portions of the at least one open circuit conductor.

The portions of the continuous conductor may be parallel to each other and to the portions of the at least one open circuited conductor.

In one embodiment, the portions in one layer may be aligned with the portions in the other layer when viewed normally of the layers.

In another embodiment, the portions in one layer may be offset perpendicularly to their parallel extents relative to the portions in the other layer when viewed normally of the layers, so as to be aligned with the adjacent edges of adjacent portions of the other layer.

Preferably the parallel portions of the conductors are pitched an equal distance apart in eachlayer the width of gaps between said adjacent edges being less than one half pitch.

The further circuit may be responsive to the capacitance between the continuous conductor and the at least one open circuited conductor, a significant change in the capacitance causing the further circuit to change state.

There may be provided a balanced capacitance measuring bridge the balance of which is disturbed if the said capacitance undergoes a significant change, the bridge then producing an output signal which if greater than a predetermined value causes the further circuit to change state.

Thus there may be a Schmitt trigger adapted to pass the output of the bridge to the further circuit.

There may be provided a trigger means adapted to compare a first voltage dependent upon the resistance of the continuous conductor with a second substantially constant voltage,

. the trigger means being adapted to cause the further circuit to change state if the resistance of the continuous conductor is significantly increased.

The first voltage may be derived from a potential divider of which the continuous conductor forms part, the second voltage being the Zener voltage developed across a Zener diode.

The trigger means may comprise a transistor operating in a switching mode and which conducts when the first voltage becomes less than the second voltage.

There may be provided a first temperature-sensitive means adapted to cause the further circuit to change state if the tem perature of the container or structure exceeds a first predetermined temperature, and/or a second temperature-sensitive means adapted to cause the further circuit to change state if the said temperature falls below a second predetermined temperature.

Preferably, the or each temperature-sensitive device comprises a respective pair of normally open contacts which when closed apply a voltage to the further circuit.

The further circuit may be adapted to destroy or characteristically mark the contents of the container on changing its state.

The further circuit may comprise an explosive fuse adapted to explode when the further circuit changes state.

The security container, or structure adapted to form part thereof may be a portable container adapted to be carried by hand.

The invention is also directed to any novel feature or combination of features herein described and/or shown in the drawings.

The invention will be described, merely by way of example, with reference to the accompanying drawings, wherein:

FIG. I shows a security container according to the inventron,

FIGS. 2a and 2b shows security circuit incorporated in the container or FIG. 1, FIGS. 20 and 2b interconnecting at A, B,

FIG. 3 shows part of the structure of FIG. 1,

FIGS. 3a and 3b are scrap plan sections of parts of the container incorporating the structure of FIG. 3, in two different embodiments.

FIG. 4 shows a further circuit incorporated in the container of FIG. 1, FIGS. 2b and 4 interconnecting at D.

FIG. 1 shows a security container 10 comprising an outer casing 12 and a removable inner tray 14, both of toughened glass fiber. The inner tray 14 has a recess or compartment 16 for containing valuable articles, particularly cash or negotiable bonds. The tray 14 is a sliding fit within the outer casing 12, and has a flanged end face 18 which abuts the end 20 of the outer casing 12 when the tray 14 is received therein. The tray 14 is locked inside the outer casing 12 by means of a suitably high-quality (e.g. l0 lever) lock 22 in the end face 18 of the tray. Alternatively, the lock 22 may be a magnetic or electrostatic lock. The container 10 is provided with a handle 24 for transportation thereof.

The inner tray comprises in its recess 16 and attached to one of the bounding thereof an explosive black powder fuse 26 which is arranged to explode if an unauthorized entry to the container is attempted. Adjacent the fuse 26 is a dye container 28 containing a quantity ofindelible dye. The container 28 and fuse 26 are separated by only a thin membrance such that if the fuse is detonated, the explosion forcibly disperses the dye throughout the recess 16, drenching its contents. The dye is of a characteristic color, rendering the contents of the container 10 instantly recognizable and, if cash, worthless to a thief. Alternatively a corrosive substance, e.g. acid may be substituted if it it is preferred to completely destroy the contents of the container 10 rather than to allow an unauthorized person access to them in any form. This is of use if the contents ofthe container are classified documents.

FIGS. 2a and 2b show the security circuit incorporated in the container 10 to react to attempted unauthorized access to the contents thereof.

The lock 22 comprises a normally open key operated switch (30 FIG. 2a) which is closed when the key is inserted in the lock and turned. If the security circuit of FIG. 3 has not previously been set in a predetermined condition, closing the switch 30 explodes the fuse 26.

The security circuit comprises a voltage source 32, e.g. a 12 volt dry battery housed in the recess 16 of the container. Across the battery 32 are connected in cascade a plurality of gating circuits 34, 36, 38, 40. Each gating circuit comprises a silicon controlled rectifier 35, 37, 39, 41, the input or anode terminals of which are respectively connected to the positive terminal of the battery 32 via respective resistors 42, 44, 46, 48. With the exception of the silicon controlled rectifier 35 of the gating circuit 34 forming the first cascade stage, the anode of each silicon controlled rectifier 37, 39, 41 of each cascade stage is also connected to the output or cathode terminals of the silicon controlled rectifier of the preceding cascade stage, this connection being in parallel with the connection ofthe silicon controlled rectifier to the positive terminal of the battery via the appropriate resistor 44, 46, 48.

The anode of the silicon controlled rectifier 35 of the first cascade stage 34 is connected, in parallel with its connection to the positive terminal of the battery, via the key operated switch 30 to a silicon controlled rectifier 50 forming part of a further circuit incorporating the fuse 26. The anode of the silicon controlled rectifier 50 is connected via the fuse 26 to the positive terminal of the battery 32. The cathode of the rectifier 50 is connected via a Zener dlode 52 to the batterys negative terminal, and to its positive terminal via a resistor 54.

The control or gating terminals of the silicon controlled rectifiers 35, 37, 39, 41 are respectively biassed from their respective cathodes via respective gate resistors 60, 62, 64, 66 and are also respectively connected to respective selectable outputs T T T and T of a l-position rotary selector switch 70 provided on the end face 18 of the inner casing 14 (FIG. 1).

The connections of the control terminals of the silicon controlled rectifiers 35, 37, 39 to the outputs T T T are via respective unilaterally conductive diodes 74, 76, 78v

The remaining selectable outputs T T T T T T are connected via a common line passing through a unilaterally conductive diode 72 to the control terminal of the silicon controlled rectifier 50.

The outputs T,,, T T, are also connected to the control terminal of the silicon controlled rectifier via respective leads from the anodes of the diodes 74, 76, 78 via further diodes 75, 77, 79.

The rotary switch 70 is connected via a pushbutton switch 80 (FIG. 1) on the end face 18 ofthe inner tray 14 to the battery positive terminal. Thus, by operating the rotary selector switch and briefly closing the Switch 80, a voltage pulse can be emitted from a chosen selectable output T --T,,.

Assuming the container to be closed and locked, the security circuit permits the container to be unlocked and opened only ifthe outputs T,, T T and T are selected in that order and the switch 80 briefly closed after each selection.

The circuit operates as follows: when the selectable output T is selected and the switch 80 briefly closed, a voltage pulse is applied to the control terminal of the silicon controlled rectifier 41, rendering it conductive and reducing the voltage at the cathode of the silicon controlled rectifier 39. If the output T is then selected and the switch 80 briefly closed a voltage pulse is applied to the silicon controlled rectifier 39, rendering it in turn conductive. if the outputs T and T are selected in turn and a similar procedure adopted, then all four silicon controlled rectifiers 35, 37, 39, 41 are rendered conductive. When the silicon controlled rectifier 35 is conductive, the voltage at its anode is reduced. The resistances 42, 44, 46, 48 are chosen such that this anode voltage is sufficiently reduced that if the key switch 30 were closed the voltage applied to the control terminal of the silicon controlled rectifier 50 would not be sufficient to make it conduct. Conversely, if the key switch 30 is closed before the silicon controlled rectifier 35 is conducting, a much higher voltage is applied to the silicon controlled rectifier 50, causing it to conduct and exploding the fuse 26. Thus, if the key switch is operated before a predetermined number (i.e. four) of the gating circuits 34, 36, 38, 40 have been rendered conductive the further circuit comprising the silicon controlled rectifier 50 and the fuse 26 changes state.

If the outputs T,, T T T are not selected in the correct order, then again the fuse 26 is made to explode. For example, if a given gating circuit (eg 38) is not conducting, then the cathode of the silicon controlled rectifier (e.g. 37) of the preceding gating circuit 36 is at the full positive voltage developed by the battery, since the gating circuit 38 represents an infinite impedance. Consequently, the control terminal ofthe silicon controlled rectifier 37 is also at substantially the full battery voltage, being connected from its cathode via the gate resistor 64. Thus when a voltage pulse is wrongly applied via output T to the diode 76, there is no potential drop across the diode which therefore does not conduct. The pulse instead passes via the diode 77 to the silicon controlled rectifier 50, causing it to conduct and explode the fuse 26.

Thus, if the voltage pulses are not applied to the gating circuits in a predetermined sequence starting with the gate 40 forming the last stage of the cascade and finishing with the gate 34 forming the first cascade stage, the further circuit 50, 26 changes state.

The resistor 54 and the Zener diode 52 ensure that the maximum forward voltage drop of the silicon controlled rectifiers 35, 37, 39, 41 in series is not quite sufficient to cause the silicon controlled rectifier 50 to conduct.

if any of the remaining outputs T T T T T T-, are selected then the voltage pulse is applied directly to the control terminal of the silicon controlled rectifier 50, exploding the fuse 26.

In order to prevent a prospective thief gaining access to the interior of the container by keeping it until the battery is exhausted, the security circuit embodies a voltage sensing circuit including a trigger to explode the fuse 26 if the battery voltage falls below a predetermined value.

A potential divider 84, 86 is disposed across the battery terminals, and biases the emitter of a transistor 88 at a constant fraction of the battery voltage. The base of the transistor 88 is connected to the junction of the Zener diode 52 and the resistor 54 and is initially at a lower potential than the emitter. The potential at the base is thus the Zener voltage and is substantially constant.

As the battery voltage falls with time, the emitter voltage of transistor 88, initially greater than the base voltage, finally falls below a substantially constant voltage which is the Zener voltage minus the emitter-base bias voltage (characteristic of the transistor) necessary for the transistor 88 to conduct. The transistor 88 then conducts, switching on a further transistor 90 and applying a voltage via the emitter-collector circuit thereof to the control terminal ofthe rectifier 50. The rectifier 50 conducts, exploding the fuse 26.

A large capacitor 92 is provided across the battery terminals to ensure that sufficient energy is available, even when after a considerable life the impedance of the battery has increased, to explode the fuse 26 when the rectifier 50 conducts.

Disposed at the walls of the outer container 12 and the tray 14 (including the end face 18 thereof) is a guard circuit such that an attempt to cut, burn or otherwise penetrate the walls of the container will result in the fuse 26 exploding. in this embodiment, the guard circuit is embedded in the walls by being moulded therein.

The guard circuit (P16. 3) comprises two'parallel layers 94 of closely spaced conductors (e.g. copper wires or strips), the layers being coextensive with each other and with the walls. One conductor 96 is electrically continuous and is convoluted, e.g. folded back upon itself. Each layer comprises two further open circuited conductors 98, having a plurality of open circuited branches. It will be appreciated that the open circuited conductors 98, 100 alternatively, or in addition to being branched may be convoluted, provided they remain, as a whole, open circuited. The conductors 96, 98, 100 are electrically separate from each other, being insulated by the glass fiber in which they are embedded.

The conductors 98, 100 are each connected at one end to a respective common lead 102, 104. The other (branched) ends 106, 108 of these conductors are left electrically discontinuous, that is to say unconnected or floating.

The conductors 96, 98, 100 have spaced apart parallel portions. The parallel portions of the conductor 96 are interposed between similarly spaced apart neighboring parallel portions of the conductors 98, 100. Consequently, an attempt to cut or drill through the walls of the container will result in the conductor 96 being severed, and/or continuity or a short circuit being established between adjacent portions of the conductors 96 and 98 or 100, exploding the fuse 26 as described hereinafter. Such a short circuit can of course occur between the conductors 96,98, 100 ofdifferent layers.

Although the conductors are shown as laminarly arranged in FIG. 3, they can of course be wrinkled in the plane of the drawing, to combat attempts to grind away the surface of the container wall until the guard circuit is completely exposed.

Referring to FIG. 3a, which shows a scrap section through a wall 93 taken perpendicularly to the conductors in the layers 94, it will be seen that the layers 94 are disposed relative to each other in the wall 93 so that the parallel portions of the conductors of one layer are aligned behind theparallel portions of the conductors of the other layer (i.e. directly one behind the other) when viewed normally of the layers. This conductor-for-conductor alignment results in the conductors presenting a confusing pattern if an attempt is made to X-ray the container to investigate its construction FIG. 3b shows an'alternative arrangement of the parallel portions of the conductors. The parallel portions of the conductors of one layer 94 are offset relative to the parallel portions of the conductors of the other layer, so as to be aligned with the adjacent edges of neighboring portions of the other layer. The parallel portions are pitched an equal distance apart in each layer, the width of the gaps between the said adjacent edges being less than one half pitch. This produces a confusing X-ray pattern of a different type.

As can be seen from .FIG. 3, the convoluted or branched pattern of the conductors is repeated at intervals, whether the conductors are arranged as in FIG. 3a or 3b. The conductor 96 is continuous throughout the repetitions of the pattern. The conductor 96 also extends through the other layer 94, although if desired a separate conductor 96a could be used, and connected in series with the conductor 96 as described hereihafter, to form an electrically continuous conductor. The exact number of layers, and the number of conductors in each layer is a matter of choice. Thus more than two open circuited conductors could be provided.

The guard circuit may extend by means of for example a connector across at least one of the interfaces between the outer casing 12 and the inner tray 14, so that any significant relative movement of the tray 14 and casing 12 (such as would occur if the tray was withdrawn from the casing) whilst the guard circuit is active breaks the continuity of the conductor 96 and results in the fuse 26 exploding.

The electrically continuous conductor 96 is connected in series with and thus effectively forms part of the potential divider 84, 86 of the trigger circuit shown in FIG. 2. Any further continuous conductors 96a may also be similarly connected; If the continuity of the conductor 96 is broken, or if its resistance is significantly increased due to it being partially cut through, then the voltage at the emitter of transistor 88 is decreased, as if the battery 32 were exhausted, and the silicon controlled rectifier 50 is caused to conduct, as described hereinbefore, exploding the fuse 26.

The conductors 98, 100 are connected via their common leads 102, 104 to the control terminal of the silicon controlled rectifier 50 (FIG. 2b). Normally there is no electrical continuity between the conductor 96 and the conductors 98, 100 and there is a very high resistance therebetween. If continuity is established however, e.g. by a would be thief trying to drill through the container 10 by means of a metal drill, or by attempting to bypass the continuous conductor 96 by injecting into the wall of the container 10 a conductive fluid, the positive battery voltage is applied via the conductors 98, 100 to the silicon controlled rectifier 50, exploding the fuse 26.

A pair of thermostats 108, 110 are provided on an inside wall of the inner tray 14.- Each comprises a respective pair of normally open contacts, one pair becoming closed if the temperature of the container 10 exceeds a predetermined value, the other pair becoming closed if the temperature of the container 10 falls below a second lower predetermined value (eg if an attempt is made to freeze the dye in the dye container 28). The pairs of contacts are connected in parallel between the battery positive terminal and the control terminal of rectifier 50. Thus if either pair of contacts close, the fuse 26 explodes.

The container 10 is also provided with a priming circuit which allows the container to be handled when opened by authorised persons. The priming circuit comprises a normally open pushbutton switch 112 (FIGS. 1 and 2b) connected in the main lead from the positive terminal of the battery. When the switch 112 is open, the security circuit of FIGS. 2a and 2b is isolated from the battery and from the capacitor 92. A relay 113 which is energized when the switch 112 is closed, is provided with a pair of hold on contacts in parallel with the switch 112. Thus, once the switch 112 has been briefly closed, the security circuit remains connected to the battery and the capacitor 92. A capacitor 114 is provided across the control and cathode terminals of the rectifier 50 to prevent any stray voltage surge that may occur when the switch 112 is closed, from causing the rectifier to conduct and exploding the fuse 26.

The lock 22 comprises a second key-operated switch 116 (FIG. 3b) having normally closed contacts 60. The lock is such that when the key is turned therein, the key operated switch 30 closes before switch 116 opens.

The switch 116 is in series with the contacts 118, and when open thus deenergizes the relay 113, allowing the inner tray 14 to be withdrawn without the fuse 26 being exploded when the continuity of the conductor 96 is interrupted. A modification of the security circuit is shown in FIG. 4. This modification makes the further circuit 50, 26 also change state in response to a significant change in another electrical property of the guard circuit, its capacitance.

In order to detect capacitance change, an alternating volt age is provided by an oscillator 120. The alternating voltage is typically sinusoidal at a frequency of'l000 Hz. The oscillator 120 comprises a pair of transistors 122, 124, the bases of which are connected via a center tapped secondary winding 128 of a three-winding transformer 126 and a resistor 130 to the positive terminal of the battery 32. The collectors of the transistors 122, 124 are similarly connected via a center tapped primary winding 132 of the transformer and a choke 136. The choke 136 is a constant current device, enabling the oscillator to produce a sinusoidal output. An approximately square wave output would be obtained if the choke were omitted.

The output ofthe oscillator 120 is applied via a DC blocking capacitor 137 across a balanced capacitance bridge 138 (e.g. a Wien bridge). A third winding 139 of the transformer 126 is also connected across the bridge 138 as shown in FIG. 4.

The bridge 138 has as one ofits arms the self capacitance of the guard circuit as measured for example between the conductor 96 and the conductors 98 and/or 100. The remaining capacitances of the bridge are chosen so that the bridge is balanced and produces no output in its different circuit. However, if the container 10 is tampered with and the capacitance between the conductor 96 and the conductors 98, 100 changes significantly (eg due to a wall of the container being deformed, or by the glass fiber insulation being partially cut away) then the bridge 138 becomes unbalanced, and produces an output. This output is amplified in an AC amplifier 140, rectified in a diode 142 and fed to a Schmitt trigger 144.

The Schmitt trigger 144 comprises a pair of transistors 146, 148, the emitters of which are biased from the negative terminal of the battery 32 via a bias resistor 15. The collector of the transistor 146 is connected to the base of the transistor 148 via a potential divider comprising resistors 152, 154. A capacitor 156 bridges the resistor 154.

The amplified rectified output of the bridge 138 is applied to the base of the transistor 146, and if it is above a predetermined threshold level chosen by suitably selecting the values of the components of the Schmitt trigger 144, the transistors 146 and 148 conduct, and apply a signal to the control terminal of the silicon controlled rectifier 50, thus detonating the fuse 26.

The capacitor 156 is provided to compensate for any stray capacitance between the base of the transistor 148 and earth (the negative terminal of the battery 32). Such a stray capacitance would reduce the steepness of the wave front of the pulse emitted by the transistor 146 when it starts to conduct with the result that the Schmitt trigger 144 may fail to trigger if a short pulse, e.g. of order milliseconds were applied to the base of the transistor 146.

An integrating capacitor 158 ensures that spurious transient signals (eg of order microseconds) that may be above the threshold level do not trigger the Schmitt trigger 144 and detonate the fuse 26.

The security container 10 specifically described herein by way of example only may have the advantage that once closed and locked by means of the lock 22, a messenger carrying the container is not required to resist an attempt to steal the container, since the thief could not gain entry to the container. Consequently, the messenger need not have the container 10 chained to his wrist, as is often the practice with known containers. Furthermore, the messenger need not take any action to protect the box, or to set off any alarm. The messenger is thus less exposed to physical danger.

It will be appreciated that the invention is applicable to other than portable containers. For example, it may be applied to a safe, either free standing or incorporated into a building, e.g. as a vault. It may also be applied to a vehicle such as a van used for transporting large amounts of cash.

Iclaim:

1. A security container provided, at a wall thereof, with a guard circuit, comprising an electrically continuous elongated convoluted conductor, and at least one open circuited elongated convoluted or branched conductor, closely proximate the continuous conductor, means insulating the continuous conductor from the open circuited conductor, a further circuit which can take more than one state, means to sense the resistance of the continuous conductor and to sense continuity between the continuous and theopen circuited conductor, and means to change the state of the further circuit in response to a change in the resistance of the continuous conductor, and in response to continuity being established between a said open circuited conductor and the continuous conductor.

2. A security container as claimed in claim I wherein the conductors are arranged in two layers, coextensive with each other and with the wall, the continuous conductor and at least one said open circuited conductor being provided in each layer.

3. A security container as claimed in claim 1 wherein the continuous conductor has a plurality of spaced apart portions, the at least one open circuited conductor also having a plurality of spaced apart portions, each portion of the continuous conductor being interposed in a respective space between neighboring portions of the at least one open circuited conductor.

4. A security container as claimed in claim 3 wherein the portions of the continuous conductor are parallel to each other and to the portions of the at least one open circuited conductor.

5. A security container as claimed in .claim 4 wherein the conductors are arranged in two layers, coextensive with each other and with the wall, the continuous conductor and at least one said open circuited conductor being provided in each layer, the portions in one layer being aligned with the portions in the other layer when viewed normally of the layers.

6. A security container as claimed in claim 4 wherein the conductors are arranged in two layers, coextensive with each other and with the wall, the continuous conductor and at least one said open circuited conductor being provided in each layer, the portions in one layer being offset perpendicularly to their parallel extents relative to the portions in the other layer when viewed normally of the layers, so as to be aligned with the adjacent edges of adjacent portions of the other layer.

7. A security container as claimed in claim 6 wherein the parallel portions of the conductors are pitched an equal distance apart in each layer, the width of gaps between said adjacent edges being less than one half pitch.

8. A security container as claimed in claim 1 comprising means to sense the capacitance between the continuous conductor and the at least one open-circuited conductor, the further circuit being adapted to change state upon a significant change in said capacitance. I

9. A security container as claimed in claim 1 comprising at least one temperature-sensitive means to sense the temperature inside the container, and means to cause the further circuit to change state when said temperature is outside a predetermined limit.

10. A security container as claimed in claim 9 wherein the temperature-sensitive means comprises a pair of normally open contacts which when closed apply a voltage to the further circuit.

11. A security container as claimed in claim 1 wherein the further circuit comprises means to destroy or characteristically mark the contents of the container on changing its state.

12. A security container as claimed in claim 11 wherein the further circuit comprises an explosive fuse adapted to explode when the further circuit changes state.

13. A security container as claimed in claim 1 the security container being a portable container adapted to be carried by hand.

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