GB2466721A - A security system for a secure unit - Google Patents

Abstract

This invention relates to a security system 10, particularly but not exclusively, for automatic teller machines, safes, safe-rooms, and safety deposit boxes 14. The system consists of piezo electric or strain gauge sensors 12 which can be retro fitted to existing structures to detect small changes in the strain of the structure from tampering to the device. The sensors can detect compression of the structure from cutting tools and expansion of the structure from heat generated by the friction of the cutting tools. The sensors are thermally insulated to stop the sensors detecting changes in the ambient conditions which may cause false attack alarms. An attached processing means 18 monitors the magnitude, polarity and rate of change of the signal and compares these to predetermined characteristics of classified attack signals to determine whether or not an attack is occurring.

Description

SECURITY SYSTEM

Field of the Invention

This invention relates to a security system, particularly but not exclusively, for secure structures such as automatic teller machines, safes, safe-rooms, and safety deposit boxes.

Prior Art

The applicant's previous UK patent application, relating to the subject-matter hereof, is published under GB-A-2 365 187. The earlier patent application discloses a security system comprising one or more piezo-electric sensors in contact with a panel of an automatic teller machine (ATM).

Sensors are connected to an electronic control circuit which processes electrical output from the sensor and selectively provides an alarm. The piezo-electric sensors sense attacks against the ATM by producing an electric charge or potential in response to changes in the structure of the panel of the ATM due to cutting tools such as angle grinders, power-saws, drills or acetylene torches. *.S. * S *5S5 *

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* The control circuit comprises four sub-channels for detecting different types of attack. The first to third sub-channels detect increasing changes in S..

the panel structure, starting with small changes detected by the first sub-* I I..

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channel to very large changes detected by the third sub-channel. A fourth sub-channel detects high frequency changes in the structure due to the cutting action of a drill bit, power-saw or grinder wheel.

In more detail, the first three sub-channels incorporate a low pass filter for filtering low frequency outputs from the sensor. A first of these sub-channels detects small structural changes due to pressure applied to a panel by a cutting tool such as an angle grinder. A second sub-channel detects larger structural changes due to a more severe attack or by rapid heating resulting from an acetylene torch or similar heat cutting devices. A third sub-channel also incorporates a low pass filter and is adapted to detect if attempts are made to move the whole ATM. A fourth sub-channel comprises a high pass filter and detects high frequency changes in panel structure due to the vibrations created when a high speed cutting tool is used.

Although successful, there were scenarios in which possible false alarms may have been triggered, for example, as a result of a combination of extreme ambient temperature fluctuations.

GB-A-2 124 763 (Securiton AG) uses a piezoelectric element as part of an acoustic sensor. The acoustic sensor detects sounds in the structure on * which the acoustic sensor is mounted. These sounds tend to either be short, high frequency or longer, lower frequency signals. The acoustic sensor * detects mechanical vibrations in the structure and cannot detect pressure or ** * I * *I* temperature changes in the structure; the latter being detected by a separate temperature monitoring circuit C. The temperature monitoring circuit C detects the magnitude of changes on the detection equipment itself. The purpose of the monitoring circuit C is therefore to identify tampering, rather than temperature effects in the structure perse.

GB-A-2 320 349 ( NCR International mc) describes a system where the walls of a safe or secure structure are formed from or include a layer of piezoelectric material to detect different types of mechanical attacks or a layer of material adapted to detect mechanical and thermal attacks. These materials are expensive and are normally incorporated with the safe or secure structure when fabricated. They have the advantage of covering the whole area of the safe or secure structure so that retro-fitting is in theory possible; in practice it is difficult and expensive.

EP-A-0 277 679 (Seculock BV) describes a device that employs a layer of piezoelectric material that covers the structure. The device ensures that an attack on the structure that crushes or damages the layer is detected, but no qualitative assessment is performed. Furthermore the material that is needed is customised and is expensive. * * * e.

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* The present invention arose in order to provide an improved security

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system for secure structures, particularly but not exclusively, for automatic OSd

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teller machines, which system improves the detection and identification of a particular attack, has improved integrity and reduces the risk of false alarms.

Summary of the Invention

According to the present invention there is provided a security system comprising: at least one sensing device which is in direct contact with a surface of a structure of a secure unit and thermally insulated from ambient changes in temperature, such that in use, said at least one sensing device generates signals in response to strain changes introduced in said structure; and a processor is adapted to receive the signals from the at least one sensing device and to classify the signals according to specified criteria; and means to derive from the classified signals and/or predetermined combinations of classified signals, the cause for the strain changes in the said structure.

Preferably the sensing device is a piezo electric transducer.

Alternatively it may be a strain gauge, an optical fibre arranged to monitor strain or any other suitable sensor arranged to provide a signal of an incremental change in the surface of the material forming the structure of the a..' secure unit. Ideally signals are classed in groups arising as a result of causes

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* of the strain. One such class is signals arising as a result of heat generated by friction of a cutting tool against the surface of the structure. Another class *5* * is signals arising as a result of heat generated by thermal cutting tools (such * ,, * .-* as oxy-acetylene cutters) imparting heat to the surface of the structure. A further class of signals arises as a result of ambient temperature changes that are for example associated with the weather. Another class of signals arises due to instantaneous or prolonged mechanical shock or force, for example as arise due to an attack with heavy objects such as a sledge hammer, pressing a cutting tool against the surface of the structure and cutting into the structure with a cutter such as a drill, angle grinder or power saw. Another class of signals arise due to noise transmitted in to the structure from tools used in an attack, for example the engine of a power saw or noises emitted by a thermal cutter in use. A still further class of signals occurs due to background ambient noise, which may arise as a result of vibrations caused by passing traffic or remote operation of plant and machinery that gives rise to transmission of intermittent mechanical shocks through the sub-soil, ground or foundations of a building.

Another example of such intermittent noise is the intermittent vibrations that arise from underground (subway) trains which vibrational energy can be coupled through foundations and structure of a building to an automatic teller machine. S...

Combinations of types of mechanical and thermal attack, amounts of * distortions, as well as the direction of distortion -whether it is positive strain

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due to expansion or negative strain due to compression -can be used to *.

provide a characteristic signature of the activity causing the signals. a..

Additionally the rate of change of distortion and time interval between types of distortion can be employed to assist in the classification of signals. In addition to the foregoing the duration of application of a particular type of force as well as the time interval between forces, may be stored on a look-up table. It is also within the scope of the invention that transforms of the signals arising from the forces may be stored, such transforms include, for example Fourier transforms.

Preferably, said sensing device and said processor are configured to detect a predetermined combination or sequence of signals. For example, signals arising as a result of the size and direction of the distortion of said structure, and the subsequent magnitude and rate of expansion of the said structure due to heat generated by friction, that may arise as a consequence of a force of a cutting tool being placed against the structure and the cutting process started.

Alternatively said sensing device and said processor are configured to detect a combination of magnitude and rate of expansion due to heat generated by friction and the size and direction of the distortion of said structure due to the force of a cutting tool against the structure and the high S...

frequency vibrations of said structure due to the effects of a tool cutting into S..... * .

the structure.

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As a result of the processor for processing said electrical output signal as part of a classification stage, a discriminator is used in order to determine the nature of an attack, with reference to the look-up table, and a decision is reached in order to determine whether a set of sensed criteria are as a result of an attack or a random combination of events. Decisions may include a probabilistic weighting function which is employed as part of the decision making process or used in the event of a decision clash' and so as to ensure that no impasse' is reached.

A neural network may be used to learn' what forces or devices give rise to which types of malicious effects as well as the types of signal arising as a result of harmless effects -such as person leaning on the structure or dropping a heavy object on it. It is apparent therefore that the system is able to recognise differences between vibrations, shocks or other transients that arise from relatively harmless events and those vibrations and changes that arise from potential or actual malicious attacks, such as those that occur as a result of vibrations form an angle grinder.

The sensing device preferably incorporates a thermal insulator to insulate the sensor from ambient temperature changes, thereby ensuring that * I S... . . . * any strains arising from thermal sources are, so far as possible, attributable S..... * S

solely to those thermal sources and minimum thermal background noise is *.I..* detected. I.. S. * S * S.. *S. *

The present invention also provides a kit for a security system comprising: a sensing device which is ideally a piezo-electric sensor, that in use directly contacts a surface of a structure of a secure unit and thermally insulated from ambient changes in temperature, such that said at least one sensing device generates signals in response to strain changes introduced in said structure; and a processor is adapted to receive the signals from the at least one sensing device and to classify the signals according to specified criteria; and means to derive from the classified signals and/or predetermined combinations of classified signals, the cause for the strain changes in the said structure.

A preferred embodiment of the invention will now be described, by way of example only, with reference to the drawings, in which:-

Brief Description of the Drawings

Figure 1 is a graph showing structural distortion changes to a panel of an secure structure, which is an automatic teller machine (ATM) sustained during an attack by a cutting tool such as angle grinder, power-saw or drill; * *** * * *S..

* Figure 2 shows a security system for detecting an attack; and * S.... * S

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* Figure 3 shows a secure unit and security system. * . S *�S

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Detailed Description of the Preferred Embodiment

In the prior art described above, the first sub-channel detects relatively small changes in the structure of a secure unit due to pressure of a cutting tool such as an angle grinder against the structure. The second sub-channel detects relatively large changes in structure due to heat generated by a heat-based cutting tool such as an acetylene torch.

The prior art is not however configured to detect changes in structure due to relatively small amounts of heat generated by friction of a cutting tool such as a grinder against the structure. The detection of such friction caused heat has been found to be a good indicator of an attack, particularly when detected in combination with changes in structure due to pressure and the presence of high frequency vibrations. The present invention detects friction caused heat and is therefore able to provide an improved security system.

Figure 1 shows a graph of changes in structural distortion, or structural displacement, of a secure unit (on the y-axis) and time (on the x-axis) during a typical attack using a cutting tool such as a grinder. It is understood that although only a single sensing device is depicted, ideally two or preferably * * S...

three independent devices are deployed in the same region of the same surface of the secure structure.

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During an attack, initially when a cutting tool is used against the secure unit, the force of the tool causes the structure to rapidly distort or to be displaced in a first direction as indicated by the positive movement at instant A in Figure 1. This distortion remains relatively constant as indicated by B in Figure 1. After a relatively short period of time, heat generated by friction of the tool against the structure causes the temperature of the structure to rise.

This temperature rise causes the structure to expand or be displaced in a second, opposing, direction at a certain rate, as indicated by the negative strain, caused by contraction (negative movement) in Figure 1, typically commencing at instant C. The change in the structure due to friction becomes greater than the change in the structure due to the force applied by the tool, giving rise to the structure displacing in a negative direction for a period of time indicated by F. Finally, as the rate of increase in temperature reduces, as a result of conduction of energy throughout the bulk of the body of the structure, the rate and magnitude of the negative displacement reduces, as indicated at D on the graph.

A further characteristic of the graph, in Figure 1, is that as the wheel of **** an angle grinder (not shown) is by its very nature a cutting tool with a rough edge, typically in the form of a cutting disc, then at all times there is superimposed on the graph a higher frequency component of distortions.

This is a complex waveform but is shown in a simple form by the inset image S.

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E, showing a sample of output at F. The inset shows a superimposed higher frequency with a period shown as C. In the case of an angle grinder, within this complex high frequency waveform, there may also be a component associated with the rotation speed of the rotating cutting disc, and a higher frequency component associated with the roughness of the cutting edge of the disc.

The characteristic signature of structural displacement defined in terms of magnitude and rate of change in both a positive direction (strain caused by expansion), due to pressure of a cutting tool, and negative displacement (strain caused by compression or recovery), due to friction induced heat of the cutting tool, together with the characteristic signature of the high frequency distortions in the structure, are sensed and recognised by embodiments of the invention and used to determine the nature of an attack against the secure unit, which is typically an ATM.

Data corresponding to the characteristic signature of different methods of attack are stored, for example in a dynamic memory or erasable programmable memory, (EPROM), so that real time detected structural ***.

* displacement can be compared with the stored, representative, data. Remote S..... * .

* updating of data stored on such memory may also be performed and as such **.S..

* relate to an alternative embodiment of the invention. In addition a database of intrinsically safe or non-threatening signatures may be stored for example for 5.

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remote access and likewise a store of classified signals relating to and arising from malicious attacks may also be stored.

Referring to Figure 3, a security system 10 is shown which comprises one or more piezo-electric sensing devices 12 for contacting or fixing to a surface of a structure of a secure unit 14, which may be an ATM, such that in use the sensing device generates an electrical output signal due to changes in the structure.

Two sensing devices 12 are shown, although only one or more than two sensing devices, may be provided depending on requirements, complexity and cost restrictions. Each sensing device 12 as shown is located proximate a hinge 16 of the secure unit where an attack against the secure unit may take place. Alternative locations of the sensing device may be appropriate depending on the nature of the secure unit and the predicted position or positions of attack.

The system 10 further comprises a processor 18 for processing the electrical output signals from the sensing devices 12 and determining the occurrence of an attack against the secure unit 14 by detecting changes of * * * the structure due to heat generated by friction of a cutting tool and/or * *I*.S * . expansive forces and/or high frequency vibrations occurring in the structure.

* ***** * The sensing devices and the control are connected by way of electrical connections 20.

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Sensing device 12 and the processor 18 are configured to detect the characteristic signature of an attack as shown generally in Figure 1. In this regard, the system detects initial contraction of the structure due to force of a cutting tool against the structure, at the hinges as shown in Figure 3.

Subsequently, the system detects expansion of the structure due to heat generated by friction of a cutting tool against the structure.

The displacement of the structure of the secure unit caused by pressure and friction induced heat is relatively small and therefore the sensing device or devices 12 are selected to be capable of sensing such displacement, which may be as small as 1-100 pm. The sensing devices 12 are also capable of sensing movement in first direction and then subsequently in a second direction. The first and second directions may be perpendicular one to another but are typically parallel when a single sensing device is used.

As the amount of heat generated by friction of the cutting tool is relatively small, the sensing device must be highly sensitive and capable of detecting changes in distortion generated by a rate of temperature change of around 10 micro-degrees Celsius per second. Such a sensing device is S.,. * S *S*.

* however susceptible to sense displacement of the structure of the secure unit **.* * * due to changes in ambient temperature. Accordingly, the sensing device * .** S. * incorporates a thermal insulator for insulating the piezo-electric sensor from ambient changes in temperature. Preferably, the thermal insulator also S..

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insulates an area of the surface of the structure around the sensor from changes in ambient temperature.

Additionally, a false alarm can be avoided, or its occurrence reduced, by assessing a combination of detected and classified signals, arising from, for example: detection of an instantaneous impulse force and subsequently, after a given time period, within a specified time window, a strain caused by friction induced heat in accordance with the characteristic signature, for example as shown in Figure 1. Such a sequence is likely to indicate that an attack is occurring; whereas if a different sequence of classified signals is detected, for example a modest shock followed by a slow thermal transient, this could indicate a window blind has been opened and thermal expansion is occurring as a result of ambient conditions.

Alternatively a person may harmlessly lean against the secure unit which may give rise to an increase in pressure. However, as this is unlikely to also give rise to any sufficient increase in temperature, such a detected event would not cause the alarm to be triggered. Further, the action of sunlight on the secure unit may cause an increase in temperature similar to an increase produced by friction induced heat. However, as such an increase in * S * temperature is not combined with a sudden initial increase in pressure, the *.S**. * *

detection of this particular sequence of signals would be determined as non-**SS..

threatening and so the alarm would not be triggered. Similarly the onset of ** * * * S..

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rise in ambient temperature is likely to be at a much lower rate of change than a thermal transient caused by local friction heating.

Additionally, a false alarm can be avoided, or its occurrence reduced, by using a combination of detected signals and/or their order of detection and/or their duration and/or the time interval (delay) between one type of signal and another. For example the signal signature in Figure 1, namely of pressure and friction induced heat and high frequency induced distortions are typical of the characteristic signature of an attack on the secure unit.

The processor 18 comprises means for processing low frequency low threshold electrical outputs from the sensing device and for comparing the historic data profiling an attack, for instance as corresponding to the graph shown in Figure 1. The processor is configured to detect relatively small outputs from the sensors due to friction induced heat preferably in combination with further relatively small outputs due to pressure. The control 18 can detect such small outputs due to both positive and negative displacement of the structure of the secure unit and compare those outputs with historical data representative of an attack. * 0. * e *.**

Alternatively, or in addition to the foregoing, the control 18 may be arranged to detect high frequency distortions and combine detected signals *..S..

with the low frequency displacements when comparing the signals with " historically collected and stored data, as part of for example a neural network. **a a

Such data may be pooled or shared between for example, similar systems or similar configurations of sensors or even location of sensors on a particular system, so that optimisation of sensors and their functionality may be achieved.

A more detailed description of one embodiment of a security system is shown in Figure 2. Figure 2 shows the arrangement of a sensing device and processor in block diagram form. It should be appreciated that this diagram is intended to demonstrate the principle of operation and that other specific configurations could be adopted in order to achieve satisfactory results.

A sensing device 12 comprising a piezo electronic sensor (I) is fixed to a plate, surface or side of an ATM or safe, H. One or more sensors may be used depending on the area to be covered, but for the purposes of the present description a single sensor is shown. A sensor is fixed to the plate using an adhesive that allows maximum surface to surface contact, so that any mechanical deflections are transferred to the sensor with the minimum of loss of signal. Cyanoacrylate adhesive known as Super-Glue (Trade Mark) is effective. * S *5S*

* The sensing device 12 incorporates thermal insulator J which as shown * . * completely covers the sensor. This insulation, for example closed cell foam, does not restrict the sensor from sensing the very small changes in the metal deformations caused by either the fluctuations in temperature as a result of * S. * friction or the force caused by a cutting tool being pressed against the structure.

The thermal insulator insulates the sensors from external temperature fluctuations such as changes in sunlight, or sudden cold draughts. Typically, the structure of the secure unit has a relatively large mass and long thermal time constant so sudden ambient temperature changes will cause slow changes in the structure.

The electrical output from the sensing device 12 is input to a charge amplifier (K) which converts the charge from the sensing device to an electrical potential. The use of very high performance operational amplifiers allows the charge amplifier and associated circuitry to detect very small changes of temperature in the presence of deflection and noise signals.

Primarily this is due to the different characteristics of these signals, and the ability to distinguish between them. For example the amount of pressure exerted by someone using an angle grinder or drill will be in the region of 7kgf. When the sensor or sensors I are fitted to 25 mm thick mild steel plate, at a distance of 25 cm an electrical output of 500pV can be expected. As a result of friction, the temperature rise can also be detected. This is shown in S...

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Figure 1 as the turning point C. * S.... * .

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Pressure causes the sensors I to deflect slightly in one direction whereas the temperature rise causes expansion in the opposite direction. *5*

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This opposes, and soon exceeds the pressure signal. In practice when using temperature rise on its own it is possible using this method to detect a rate of temperature change of around 10 micro-degrees Celsius per second. The thermal insulator allows such sensitivity by insulating the sensors from external temperature fluctuations such as changes in sunlight, or sudden cold draughts.

Typically, the structure of the secure unit has a relatively large mass and long thermal time constant. Often the secure unit is made from mild steel which is not a good conductor of heat. Accordingly, the heat is confined to the area where the activity is taking place and is duly transferred to the sensor.

The output from the charge amplifier is input to an analogue-to-digital converter (ADC) M via a variable attenuator L. The variable attenuator (L) maintains the input to the AID converter within operating parameters in a similar way to automatic gain control.

The output from the AID converter is filtered by suitable filters (N) separating higher frequency signals due to the rotational frequencies associated with cutting tools, and the lower frequency signals due to the effects of pressure and heating trends. Real time monitored signals are S..... compared by comparator P with pre-loaded historic data (e.g. profile tables in * S. SS.

* accordance with Figure 1) stored as a look-up table in memory 0.

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The comparator can determine the presence of high frequency (HF) noise consistent with an angle-grinder or drill, the presence of pressure due to the requirement to push against the surface being cut and also the abnormal temperature rise associated with the friction due to cutting. If the determination is positive, the comparator outputs to an output stage (Q) which may include an alarm and additional outputs indicative of the nature of the alarm.

It should also be noted that whilst an attack on a safe with an oxy-acetylene burner or thermal lance produces no pressure and little high frequency distortions, there will be enormous output due to the sudden increase in heat at such a rate of change as to be instantly recognizable by the comparator logic. Similarly a violent action such as a ram-raid' would cause an unmistakably sudden large output signal due to an inordinate pressure rise. All these extreme events are also included in the look-up table.

It will be appreciated that the embodiments described herein are able to distinguish between false alarms and actual attacks.

The invention has been described by way of several embodiments, with modifications and alternatives, but having read and understood this S...

description of further embodiments and modifications will be apparent to those * S skilled in the art. For example, redundancy of sensors and other circuitry may be built into the alarm so that in the event of a failure of one component a * S. * S *.* * a signal from a second component may be used. The alarm may be remotely accessed, eg via a hardwire or radio frequency (RF) connection. Likewise a probabilistic assessment of signals may be made in order to assist in discrimination, for example in the event that a clear assessment is not obtainable. Similarly the invention may be supplied as a kit suitable for retro-fitting and upgrading existing systems.

It will be appreciated that although reference throughout has been made to a piezo electric sensor alternative sensors may be employed, such as strain gauges or optical sensors.

Further variation may be made to the invention by including a central, remote database of classified threatening and non-threatening signals.

All such embodiments and modifications are intended to fall within the scope of the present invention as defined in the accompanying claims. * * **** *

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Claims (6)

1. Claims 1. A security system comprises: at least one sensing device which is in direct contact with a surface of a structure of a secure unit and thermally insulated from ambient changes in temperature, such that in use, said at least one sensing device generates signals in response to strain changes introduced in said structure; and a processor is adapted to receive the signals from the at least one sensing device and to classify the signals according to specified criteria; and means to derive from the classified signals and/or predetermined combinations of classified signals, the cause for the strain changes in the said structure.
2. 2. A security system as claimed in claim I wherein the sensing device includes a piezo-electric sensing device.
3. 3. A security system as claimed in claim I wherein the sensing device includes a strain gauge.
4. 4. A security system as claimed in any preceding claim wherein the processor measures the magnitude, polarity and rate of change of signals,
5. 5. A security system as claimed in any preceding claim is adapted to receive data from and send data to a database of classified signals. S...
6. 6. A security system as claimed in any preceding claim wherein said sensing device is configured to detect expansion of said structure due to heat * S.... * .:. generated by friction of a cutting tool against the structure. * S S..S7. A security system as claimed in any preceding claim wherein signals are classed in groups arising as a result of: heat generated by friction of a cutting tool against the structure; signals arising a result of ambient temperatures; signals arising due to instantaneous mechanical shock; signals arising due to prolonged mechanical shock; sustained force; impact; cuffing; noise and vibration; and signals due to background ambient vibration.8. A security system as claimed in claim 7 wherein said processor is configured to detect a predetermined combination of signals.9. A security system as claimed in claim 7 or 8 wherein said processor is configured to detect a combination of expansion due to heat generated by friction and distortion of said structure due to the force of a cutting tool against the structure and high frequency vibrations of said structure due to the effects of a tool cutting into the structure.10. A security system as claimed in either claims 8 or 9 includes a means for determining a combination of types of forces, amounts and polarity of distortions and time intervals. a.11. A security system as claimed in any preceding claim has access to a S.....* S database of signals stored in the form of a look-up table.S..... * S S..S a. * S * .**S ** *12. A kit for a security system comprising: at least one sensing device which is in direct contact with a surface of a structure of a secure unit and a thermally insulator for insulating the sensing device from ambient changes in temperature, such that in use, said at least one sensing device generates signals in response to strain changes induced in said structure; and a processor is adapted to receive the signals from the at least one sensing device and to classify the signals according to specified criteria; and means to derive from the classified signals and/or predetermined combinations of classified signals, the cause for the change in the said structure.13. A kit as claimed in claim 12, wherein said thermal insulator comprises insulating foam.14. A kit as claimed in claim 12 or 13, comprising an adhesive for adhering the sensing device to the surface of the secure unit.14. A security system or kit substantially as herein described with reference to the Figures. * * S...*5***S * ISS..... * I I..S I. * S 1.0II