US3559593A

US3559593A - Security container

Info

Publication number: US3559593A
Application number: US841878A
Authority: US
Inventors: Edward A Munton; Alan Birt Acres
Original assignee: Vigil Security Ltd
Current assignee: Vigil Security Ltd
Priority date: 1968-07-18
Filing date: 1969-07-15
Publication date: 1971-02-02
Anticipated expiration: 1988-02-02
Also published as: GB1248763A

Abstract

A portable security container adapted to contain valuable articles and comprising a lock which when opened permits access to the interior of the container, a security circuit comprising a plurality of gating circuits, means adapted to apply a voltage from a voltage source within the container to each gating circuit to render it conductive, a further circuit which can take more than one state and which is arranged to change state if the voltage is not applied to the gating circuits in a predetermined sequence, and if the lock is opened before a predetermined number of gating circuits have been rendered conductive, means adapted to destroy or characteristically mark the contents of the container upon said change of state of the further circuit, and voltage-sensing means to cause the further circuit to change state if the said voltage falls below a predetermined value.

Description

United States Patent 1,606,516 11/1926 Daly Inventors Edward A. Munton Thorpe Bay. Essex; Alan Birt Acres, Leigh-on-sea Essex, England Appl. No. 841,878 Filed July 15, 1969 Patented Feb. 2, 1971 Assignee Vigil Security Limited Sussex, England a British company Priority July 18, 1968 Great Britain 34283/68 SECURITY CONTAINER 10 Claims, 7 Drawing Figs.

US. Cl 109/25, 109/42, 109/44; 317/134 Int. Cl E05g 3/00 Field of Search 109/25, 29, 35, 42, 44; 70/278; 317/134, 135; 340/280 References Cited UNITED STATES PATENTS Primary Examiner-David .l Williamowsky Assistant ExaminerPhilip Cl Kannan Atr0rney-Cushman, Darby & Cushman ABSTRACT: A portable security container adapted to contain valuable articles and comprising a lock which when opened permits access to the interior of the container, a security circuit comprising a plurality of gating circuits, means adapted to apply a voltage from a voltage source within the container to each gating circuit to render it conductive, a further circuit which can take more than one state and which is arranged to change state if the voltage is not applied to the gating circuits in a predetermined sequence, and if the lock is opened before a predetermined number of gating circuits have been rendered conductive, means adapted to destroy or characteristically mark the contents of the container upon said change of state of the further circuit, and voltage-sensing means to cause the further circuit to change state if the said voltage falls below a predetermined value.

PATENTEDFEB mm SHEET 1 [IF 5 SECURITY CONTAINER This invention relates to a portable security container.

In one aspect, although not so restricted. the invention provides a portable security container adapted to contain valuable articles and comprising a lock which when opened permits access to the interior of the container. a security circuit comprising a plurality of gating circuits. means adapted to apply a voltage from a voltage source within the container to each gating circuit to render it conductive, a further circuit which can take more than one state and which is arranged to change state either if the voltage is not applied to the gating circuits in a predetermined sequence. or if the lock is opened before a predetermined number of gating circuits have been rendered conductive. means adapted to destroy or characteristically mark the contents of the container upon said change of state of the further circuit, and voltage-sensing means to cause the further circuit to change state if the said voltage falls below a predetermined value.

There may be a selector device having a plurality of outputs. some of which are selectable to apply respectively the said voltage to respective gating circuits, other outputs being connected to the further circuit whereby if a said output is selected and the said voltage applied thereto. the further circuit changes state.

The gating circuits may be arranged in cascade. an input terminal of each gating circuit being respectively connected to one terminal of the voltage source. the input terminals of the gating circuits, with the exception of the input terminal of that gating circuit forming the first cascade stage. each also having a respective parallel connection to an output terminal of the gating circuit of the preceding cascade stage, the said predetermined sequence starting with the gating circuit forming the last cascade stage and finishing with the gating circuit forming the first cascade stage.

The input terminal of each gating circuit may be an anode terminal, the output terminal being a cathode terminal, each gating circuit also having a respective control terminal, the control terminal being connected to the respective cathode terminal via a bias resistor and, except in the gating circuit forming the last cascade stage, being adapted to receive respectively the said voltage via a respective unilaterally conductive device arranged so that it only conducts if the potential at the control terminal is less than the potential at the anode terminal, the said voltage, when the said device is nonconductive being fed to the said further circuit to change the state thereof.

The said further circuit may comprise at least one siliconcontrolled rectifier, the cathode terminal of the gating circuit forming the last stage of the cascade being connected to the other terminal of the voltage source, the cathode of a siliconcontrolled rectifier of the further circuit also being connected to the said other terminal via a zener diode.

The cathode of the said silicon-controlled rectifier of the further circuit may be connected to the said one terminal of the voltage source via a further bias resistor, in parallel with its connection to the said other terminal.

The further circuit may comprise a control terminal to which are connected, in parallel, the said other outputs of the selector device and respective leads each adapted to receive the said voltage when the said respective unilaterally conductive device is nonconductive.

The voltage-sensing means may be adapted to compare a first voltage having a fixed relation to the voltage of the voltage source with a second substantially constant voltage, a trigger means causing the further circuit to change state when the first voltage becomes less than the second voltage.

There may be a potential divider connected across the terminals of the voltage source to derive the first voltage, the second voltage being the Zener voltage of the said Zener diode.-

The further circuit may comprise an explosive fuse which is arranged to explode when the further circuit changes state to release into the interior of the container an indelible dye or a corrosive substance.

The security container may be provided with a guard circuit comprising an electrically continuous elongated convoluted conductor. and at least one open-circuitcd elongated convoluted or branched conductor closely proximate the continuous conductor but insulated therefrom, the further circuit 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.

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 layerv 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 invention;

FIGS. 2a and 2b show a security circuit incorporated in the container of FIG. 1, FIGS. 2a and 2b interconnecting at A, B, C;

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; and

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

FIG. I shows a security container 10 comprising an outer casing 12 and a removable inner tray 14, both of toughened glass fibre. 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 Y 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. 10 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 walls 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 of indelible dye. The container 28 and fuse 26 are separated by only a thin membrane 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 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 of the container are classified documents.

FIGS. 2a and 21; 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 v. 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

siliconcontrolled 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 siliconrcontrollcd rectifier of the preceding cascade stage. this connection being in parallel with the connection of the silicon-controlled rectifier to the positive terminal of the battery via the appropriate resistor 44. 46. 48.

The anode of 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 diode 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 biased 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 lO-position rotary selector switch 70 provided on the end face 18 of the inner casing 14 (FIG. 1). I

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, 78.

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 push button switch 80 (FIG. 1) on the end face 18 of the 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 if the 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 tenninal 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. 1f 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 suffi' ciently 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.

1f 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 (e.g. 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 of the 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 siliconcontrolled 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. l 3

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 theremaining 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 ex hausted, 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 re-' sistor 54 and is initially at a lower potential than the'ernitter. The potential at the base is thus the Zener voltage and is substantially constant. 7

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 of the 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 (FIG. 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. foldedback upon itself. Each layer comprises two further open-circuited

conductors

98, 100 having a plurality of opencircuited 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 fibre 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 theses 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 coursc occur between the conductors 96. 98, 100 of different layers. 7 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 the parallel 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 10 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 offsetrelative to the parallelportions of the conductors of the other layer, so as to be aligned I 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 960 could be used, and connected in series with the conductor 96 as described hereinafter, 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 efiectively forms part of the

potential divider

84, 86 of the trigger circuit shown in FIG. 2. Any further sontinuous conductors 96a may also be similarly connected. If she continuity of the conductor 96 is broken, or if its resistance issignificantly 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 siliconcontrolled 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 tem' perature 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 (e.g.

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 the 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 authorized persons. The priming circuit comprises a normally open push button switch 112 (FIGS. 1 and 2h) connected in the main lead from the positive terminal of the battery. When the switch 112 is open. the security circuit of FIGS. 20 and 2h 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. 4

The lock 22 comprises a second key-operated switch 116 (FIG. 2b) having normally closed contacts. 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 voltage is provided by an oscillator 120. The alternating voltage is typically sinusoidal at a frequency of 1,000 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 centertapped primary winding 132 of the transformed 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 of the 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 one of its 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 difference circuit. However, if the container 10 is tampered with and the capacitance between the conductor 96 and the

conductors

98, 100 changes significantly (e.g. due to a wall of the container being deformed, or by the glass fibre 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 ofthe 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. c.g. of order milliseconds were applied to the base of the transistor 146.

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

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 freestanding 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.

We claim:

l. A portable security container adapted to contain valuable articles and comprising a lock which when opened permits access to the interior of the container, a security circuit compris-' ing a plurality of gating circuits, a voltage source within the container, means to apply a voltage from said source to each gating circuit to render it conductive, a further circuit which can take more than one state and which is adapted to change state if the voltage is not applied to the gating circuits in a predetermined sequence, and if the lock is opened before .a predetermined number of gating circuits have been rendered conductive, means controlled by the further circuit and adapted to destroy or characteristically mark the contents of the container upon said change of state of further circuit, and voltage-sensing means to sense said voltage and adapted to cause the further circuit to change state if the said voltage falls below a predetermined value.

2. A portable security container as claimed in claim 1 and comprising a selector device having a plurality of outputs, some of which are selectable to apply respectively the said voltage to respective said gating circuits, other outputs being connected to the further circuit whereby if a said other output is selected and the said voltage applied thereto, the further circuit changes state.

3. A portable security container as claimed in claim 1 wherein the gating circuits are arranged in cascade, an input terminal of each gating circuit being respectively connected to one terminal of the voltage source, the input terminals of the gating circuits, with the exception of the input terminal of that gating circuit forming the first cascade stage. each also having a respective parallel connection to an output terminal of the gating circuit of the preceding cascade stage, the said predetermined sequence starting with the gating circuit forming the last cascade stage and finishing with the gating circuit forming the first cascade stage.

4. A portable security container as claimed in claim 3 wherein the input terminal of each gating circuit is an anode terminal, the output terminal being a cathode terminal, each gating circuit also having a respective control terminal. the control terminal being connected to the respective cathode terminal via a bias resistor and, except in the gating circuit forming the last cascade stage, being adapted to receive respectively the said voltage via a respective unilaterally conductive device adapted to conduct only if the potential at the control terminal is less than the potential at the anode terminal, and means to feed the said voltage, when the said device is nonconductive. to the said further circuit to change the state thereof.

5. A portable security container as claimed in claim 4 wherein the said further circuit comprises at least one silicon controlled rectifier, the cathode terminal of the gating circuit forming the last stage of the cascade being connected to the other terminal of the voltage source, the further circuit comprising a silicon-controlled rectifier, the cathode of which is also connected to the said other terminal via a Zener diode.

6. A portable security container as claimed in claim 5 wherein the cathode of the said silicon-controlled rectifier of the further circuit is connected to the said one terminal of the voltage source via a further bias resistor, in parallel with its connection to the said other terminal.

7. A portable security container as claimed in claim 4, comprising a selector device having a plurality of outputs, some of which are selectable to apply respectively the said voltage to respective gating circuits, other said outputs being connected to a control terminal of the further circuit, there also being connected to said terminal respective leads each adapted to receive the said voltage when the said respective unilaterally conductive device is nonconductive.

8. A portable security container as claimed in claim 1 comprising means to provide a first voltage having a fixed relation to the voltage of the voltage source and means to provide a second substantially constant voltage, the sensing means being adapted to compare said first and second voltages, the sensing means comprising trigger means adapted to cause the further circuit to change state when the first voltage becomes less than the second voltage.

9. A portable security container as claimed in claim 8 comprising a potential divider connected across the terminals of the voltage source to derive the first voltage, and a Zener diode, the second voltage being the Zener voltage of the said Zener diode.

10. A portable security container as claimed in claim 1 wherein the further circuit comprises an explosive fuse, means to explode said fuse when the further circuit changes state to release into the interior of the container an indelible dye or a corrosive substance.

Claims

1. A portable security container adapted to contain valuable articles and comprising a lock which when opened permits access to the interior of the container, a security circuit comprising a plurality of gating circuits, a voltage source within the container, means to apply a voltage from said source to each gating circuit to render it conductive, a further circuit which can take more than one state and which is adapted to change state if the voltage is not applied to the gating circuits in a predetermined sequence, and if the lock is opened before a predetermined number of gating circuits have been rendered conductive, means controlled by the further circuit and adapted to destroy or characteristically mark the contents of the container upon said change of state of further circuit, and voltage-sensing means to sense said voltage and adapted to cause the further circuit to change state if the said voltage falls below a predetermined value.

3. A portable security container as claimed in claim 1 wherein the gating circuits are arranged in cascade, an input terminal of each gating circuit being respectively connected to one terminal of the voltage source, the input terminals of the gating circuits, with the exception of the input terminal of that gating circuit forming the first cascade stage, each also having a respective parallel connection to an output terminal of the gating circuit of the preceding cascade stage, the said predetermined sequence starting with the gating circuit forming the last cascade stage and finishing with the gating circuit forming the first cascade stage.

4. A portable security container as claimed in claim 3 wherein the input terminal of each gating circuit is an anode terminal, the output terminal being a cathode terminal, each gating circuit also having a respective control terminal, the control terminal being connected to the respective cathode terminal via a bias resistor and, except in the gating circuit forming the last cascade stage, being adapted to receive respectively the said voltage via a respective unilaterally conductive device adapted to conduct only if the potential at the control terminal is less than the potential at the anode terminal, and means to feed the said voltage, when the said device is nonconductive, to the said further circuit to change the state thereof.

5. A portable security container as claimed in claim 4 wherein the said further circuit comprises at least one silicon-controlled rectifier, the cathode terminal of the gating circuit forming the last stage of the cascade being connected to the other terminal of the voltage source, the further circuit comprising a silicon-controlled Rectifier, the cathode of which is also connected to the said other terminal via a Zener diode.