CROSS-REFERENCE(S) TO RELATED APPLICATIONS

This application claims priority from South African provisional patent application number ZA2021/09448, filed on 2021/1 1/24, and South African provisional patent application number ZA2022/1 1018, filed on 2022/10/10, which are incorporated by reference herein.

FIELD OF THE INVENTION

This invention relates to alarm systems. More particularly, but not exclusively, this invention relates to armed mechanisms for door locks through which attempted forced entry may be detected and an alarm signal activated.

BACKGROUND TO THE INVENTION

Security for doors, windows, gates, etc. (barriers) have become necessary as a result of criminal activity. The pin tumbler lock is arguably one of the earliest forms of security systems, and paved the way for more modern barrier locks. The pin tumbler lock was initially used as an anti-theft device for locking the doors of vaults, tombs, or other safe storage units, allowing only a key holder to unlock and open the barrier door. However, this did not stop theft attempts, and thieves and burglars still managed to break into locked storage units, most of which attempts lead to breaking the lock or damaging the associated barriers in the process.

Alarm systems were the next significant evolution in security systems. Earlier alarm systems included the placement of contact or magnetic sensors on doors and/or door frames, which would send electrical signals to silent alarms and/or a sirens in order to alert people of unauthorised entry. Where the barriers associated with the sensors happen to have been locked, intruders either had to pick or break the lock to get through the barriers, which in most cases damaged the door, gate, frame or lock components associated with the barrier.

The applicant is also aware of prior art systems incorporating switches within the catches of a barrier locking mechanism. These switches may also be configured to trigger alarm signals. However, these prior art systems generally suffer from the disadvantage that they cannot discriminate between forces of different magnitudes and are therefore also affected by normal impacts associated with everyday use of the barriers or simply the environmental conditions to which they are subjected. This results in a high incidence of false alarms. In addition these systems typically have to be manually reset after having been triggered which is inconvenient to users.

In further applications, magnetic contact plates are attached to a door, gate or window (barrier), with a first plate attached to a portion of the barrier and a second plate attached to the barrier frame. When the barrier is closed, the magnetic plates make contact and trigger an alarm once separated. The barrier must be closed to arm the magnetic security system, and the security system must be deactivated to open the barrier without triggering the alarm.

The above systems have a number of drawbacks, which leave room for improvement. Most notably, the known systems lead to a high incedence of false alarms as many of them can easily be triggered under normal operating conditions, such as open and closing doors with a larger than usual force (slamming) or adverse environmental conditions such as strong winds or gusts. Furthermore, the known systems that include alarm activation buttons within door latches suffer the disadvantage that they have to be manually armed, or reset and re-armed once activated.

The preceding discussion of the background to the invention is intended only to facilitate an understanding of the present invention. It should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was part of the common general knowledge in the art as at the priority date of the application.

SUMMARY OF THE INVENTION

In accordance with an aspect of the present disclosure there is provided a strike plate for a barrier latch assembly, comprising: a catch configured to receive a latch associated with a moveable barrier; at least one carriage positioned to receive a force imparted on the barrier and be displaced at least partly by the latch under application of the force; and a sensor positioned on or opposite the carriage, wherein the carriage is biased towards a first position in which the sensor is not contacted, moveable against the bias to a second position in which the sensor is contacted when the force is applied to the barrier, and capable of returning to the first position under its bias once the force has been removed, and wherein the sensor is configured to be connected to an external alarm system and transmit an alarm signal to the alarm system when the sensor is contacted.

The sensor may be configured to transmit the alarm signal to the alarm when contacted, and set to an armed state when not contacted. The carriage may be biased with a biasing force which may be less than a breaking point of any one or more of the latch assembly, the latch, the strike plate, the barrier, a barrier frame, the carriage and/or any other component of the strike plate or barrier.

The carriage may be biased by means of at least one resiliently deformable component which may be located within the strike plate.

The sensor may be located on the carriage.

The carriage may be at least partially located within a protective cover, wherein the cover may be positioned to receive the force applied to the barrier and wherein the cover may be in turn positioned to impart a linear force on the carriage under the application of the force.

The carriage may be biased with a threshold biasing force greater than 250N.

The threshold biasing force may be between 300N and 500N.

The threshold biasing force may be between 380N and 41 ON.

The threshold biasing force may be about 390N.

The carriage may be biased by one or more coil springs.

The sensor may be a microswitch.

In accordance with another aspect of the present disclosure there is provided a method for arming a strike plate of a barrier latch assembly, the method including the steps of: positioning a carriage in the strike plate to receive a force imparted on the barrier and be displaced at least partly by a latch of the barrier under application of the force; providing a sensor in the catch and configuring the sensor to activate upon displacement of the carriage by a predetermined distance; biasing the carriage towards a first position in which the sensor is not contacted, to be moveable against the bias to a second position in which the sensor is contacted when the force is applied to the barrier, and to be capable of returning to the first position under its bias once the force has been removed; and connecting the sensorto an external alarm system which will triggerwhen the sensor is contacted. The method may include providing a cover and at least partially positioning the carriage within the cover, and configuring the cover to transfer the force to the carriage.

The method may include biasing the carriage with one or more coil springs.

The method may include biasing the carriage with a threshold biasing force greater than 250N.

The method may include biasing the carriage with a threshold biasing force of between 300N and 500N.

The method may include biasing the carriage with a threshold biasing force of between 380N and 410N.

The method may include biasing the carriage with a threshold biasing force of about 390N.

In accordance with yet another aspect of the present disclosure there is provided an alarm system incorporating one or more strike plates as defined above, each strike plate being fitted to one or more barriers associated with an area or property to be secured, wherein each strike plate is connected to an alarm system controller of the property or area, thereby enabling the system to detect forced entry through any one of the barriers.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Figure 1 is a front view of an example door latch;

Figure 2 is a bottom view of the example door latch of Figure 1 ;

Figure 3 is a front view of an armed strike plate including a conductive, carriage in use with the door latch of Figure 1 ;

Figure 4 is a bottom view of the door latch and armed strike plate of Figure 3;

Figure 5 is a cross-sectional view of the armed strike plate of the door latch of Figure 3; Figure 6 is a cross-sectional side view of the armed strike plate of the door latch of Figure 3;

Figure 7 is a top view of the armed strike plate of the door latch of Figure 3;

Figure 8 is a left-side view of an armed strike plate as described in an example embodiment of the present disclosure;

Figure 9 is a three-dimensional view of the armed strike plate of Figure 8;

Figure 10 is a left-side view of a carriage of the armed strike plate of Figure 8;

Figure 11 is an exploded view of the carriage of Figure 8;

Figure 12 is a cross-sectional view of the carriage of Figure 8;

Figure 13 is a rear view of a carriage of the armed strike plate of Figure 8;

Figure 14 is a side view of an armed strike plate for use with a hook-like latch, as described in another example embodiment of the present disclosure;

Figure 15 is an exploded side view of the armed strike plate of Figure 14;

Figure 16 is a front view of the armed strike plate of Figure 14;

Figure 17 is a rear view of the armed strike plate of Figure 14;

Figure 18 is a three-dimensional view of the armed strike plate of Figure 14;

Figure 19 is an explored three-dimensional view of the armed strike plate of Figure 14;

Figure 20 is a top view of the armed strike plate of Figure 14;

Figure 21 is a bottom view of the armed strike plate of Figure 14;

Figure 22 is an exploded top view of the armed strike plate of Figure 14; Figure 23 is an exploded bottom view of the armed strike plate of Figure 14;

Figure 24 is a side view of an armed strike plate for use with an undercut spigot, as described in a further example embodiment of the present disclosure;

Figure 25 is a front view of the armed strike plate of Figure 24;

Figure 26 is a top view of the armed strike plate of Figure 24;

Figure 27 is a rear view of the armed strike plate of Figure 24;

Figure 28 is an exploded side view of the armed strike plate of Figure 24;

Figure 29 is an exploded top view of the armed strike plate of Figure 24;

Figure 30 is a three-dimensional view of the armed strike plate of Figure 24; and

Figure 31 is an exploded three-dimensional view of the armed strike plate of Figure 24.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

An armed strike plate for a latch door latch is disclosed in this description. As used in this disclosure, the term “door latch” should be broadly construed to include any type of mechanical hardware used to fasten doors or other barriers and keep them shut. A door latch as used in this disclosure typically uses a fastener attached to two ordinarily separated surfaces, most often the door and the frame, to prevent the door from swinging or sliding open, as the case may be, while still allowing normal operation when the latch is released. Similarly, the term “strike plate” should be broadly construed to include any piece of hardware that works with a lock to keep a door secure. Strike plates are typically installed in or on the door frame, and contain a hole or other receiving formation, often referred to as a “catch”, which receives a latch, bolt or mechanical equivalent associated with a latch or lock.

The strike plate may include a catch, which may receive a latch, latch tongue or bolt, and a striker (or strike), which may affix the strike plate to a barrier frame. The barrier may be a door, a gate, a window, or the like, and the barrier frame may be a door frame, a window frame, a gate frame, or the like. Where reference is made in this specification to a “door”, it should be understood that what is described with reference to the door may equally be applied to a window, gate or other barrier, as the case may be. The terms “door” and “barrier” should be ascribed in a similar meaning in the remainder of this specification and may be used interchangeably. Likewise, in the remainder of the specification the terms “latch”, “latch tongue" and “bolt” will be used interchangeably to make it clear that the invention disclosed applies to any kind of latch arrangement in which a latch or bolt is received within a catch associated with a strike plate.

In this disclosure, a carriage or other moveable member may be at least partially accommodated within the catch, in a position where it may be contacted by the latch tongue, bolt or similar mechanical mechanism. The carriage may be biased to resist displacement and return to its original position after having been temporarily displaced. The bias may be achieved by a biasing mechanism, which in some embodiments may be resiliently flexible springs or their mechanical equivalent. The carriage may be displaced when a linear force greater than a threshold resistive force exerted by the biasing mechanism is applied to the carriage. The armed strike plate may include a sensor which may be connected to an alarm system, electrically or electronically. The displacement of the carriage may activate the sensor, which may, in turn, initiate a signal to be transmitted to the alarm systems and thereby triggering an alarm. When the linear force applied to the carriage is relieved or sufficiently relaxed to be less than the threshold resistive force, the spring-biased carriage may return to its original location in the strike plate, thereby automatically re-arming the strike plate for further use.

An example embodiment of a typical door latch used for locking doors is illustrated in Figures 1 and 2. The latch (10) includes a first latch portion (12) which may be secured to a door and a strike plate (14) which may be secured to a door frame. The strike plate (14) includes a catch (18) which is configured to receive a latch tongue (16) of the latch (10) and upon doing so securing the door shut. The latch tongue (16) is typically actuated between an engaged and disengaged condition from the catch (18) by turning a turning knob (19).

It should be appreciated that the example embodiment illustrated in Figures 1 and 2 is for illustrative purposes and should not be seen as limiting the scope of this disclosure. The invention may be used for any barrier lock (door lock, gate lock, window lock, or the like) configuration using a latch mechanism.

An example embodiment of an armed strike plate (20) for a door lock of the type illustrated in Figures 1 and 2, is illustrated in Figures 3 to 7. In the figures, the strike plate (20) includes a catch (28) which is configured to receive the latch tongue. The catch (28) includes a carriage (21), which is movably secured within the strike plate (20) by means of two screws (22). The catch (28) further includes one or more springs (23), in the current embodiment two biasing springs (23), in the current example positioned around the securing screws (22), which bias the carriage (21) away from a sensor (24) located within the catch opposite the carriage (21). The sensor (24) may be electrically connected to an alarm system by means of suitable wiring, or other electronic communications. When the door is closed and the latch tongue located within the catch (28), the latch tongue may contact, or otherwise be located close to the carriage (21) with the biasing springs (23) in their extended position. When an external, lateral force is applied to the barrier, the latch tongue will engage the carriage (21), imparting the force on the carriage (21). If the lateral force is sufficient to overcome the biasing force of the springs (23), the carriage will move towards the sensor (24) against the bias from the springs.

In the current embodiment the sensor (24) may be either a microswitch or an ignition point manufactured from a conductive material. In the latter case, the ignition point may be an electrically conductive metal pin, which forms an in-series circuit with a sensor input of the alarm system, such that when the carriage contacts the ignition point, the alarm system may receive a sensor input and be triggered. It should be appreciated that in such an embodiment the carriage may likewise be manufactured from a conductive material, thereby allowing it to make electrical contact with the conductive metal pin when contacting it. In the alternative embodiment the sensor (24) may be a microswitch connected to the sensor input of the alarm system. The microswitch may simply be activated by the carriage (21) contacting it, thereby alleviating the need for the carriage to itself be electrically conductive.

If the force applied to the carriage (21), as translated from the lateral force imparted to the door by for example a push, kick or otherwise large enough impact, is greater than a threshold biasing force of the springs (23), the springs (23) will deform sufficiently to allow the carriage (21) to contact the sensor (24). When the force is released, the force imparted on the carriage (21) will similarly be released and the carriage (21) will be allowed to return to its original position within the catch (28) by virtue of the biasing springs (23), thereby automatically breaking the contact with the sensor (24) and arming the strike plate (20) for further use.

It should be appreciated that by biasing the carriage (21) with an optimal biasing force, accidental displacement of the carriage under lateral forces associated with normal operation such as normal pushing against the door, wind and the like, and associated accidental triggering of the alarm may be prevented. At the same time, such an optimal biasing force may also allow the carriage the activate the sensor under lateral forces large enough to probably not be associated with normal, everyday use, but small enough so as not to cause damage to the door, door frame or latch parts, thereby allowing the mechanisms to be re-used repeatedly without having to replace any of the parts. More details of what could constitute such an optimal biasing force are presented in more detail further below.

A further example embodiment of an armed strike plate (100) according to this disclosure is shown in Figures 8 to 13. The strike plate (100) includes a striker (102), which fixes the strike plate (100) to a barrier frame. The strike plate (100) further comprises a carriage (106) located within a protective cover (104). The cover (104) is attached to an operatively rear portion of the striker (102) and, together with the striker (102), forms a catch (108) for receiving a latch tongue, the latch tongue forming part of the latch which is, in turn, affixed to the barrier. When the catch (108) receives the latch tongue, the latch is in a locked or engaged condition, securing the barrier to the barrier frame and preventing the opening of the barrier. When positioned within the cover (104), at least one side edge of the carriage (106) is exposed and protrudes past an edge of the catch (108) as can be more clearly seen in Figure 8, so as to be able to contact the latch tongue when the latch tongue is engaged with the catch (108).

As before, the carriage (106) is spring biased with one or more springs (1 16), in the current embodiment with two springs (116), to resist displacement under normal operating conditions. As mentioned above, at least a side edge portion of the carriage (106) is exposed and protrudes past an edge of the catch (108), thereby enabling contact between the latch tongue and carriage (106). If a lateral force is exerted on the barrier to which the latch carrying the latch tongue is secured, the latch tongue applies a linear force on the carriage (106) against the biasing force provided by the springs (116). The external force applied to the barrier may for example be associated with attempted forced entry, such as an intruder applying force to the barrier by kicking it or ramming it with the shoulder, or forces associated with normal, everyday use. When the lateral force is applied to the barrier, the resistive, biasing force is exerted on the carriage (106) by the springs (116), in the opposite direction of the linear force imparted by the latch tongue on the carriage (106). If, as mentioned above, the biasing force is sufficiently strong, it may prevent accidental displacement of the carriage (106). When the linear force exceeds a threshold force at which it overcomes the biasing force, the force by which the springs (1 16) will start to deform, the carriage (106) may be displaced in the direction of the linear force.

In the present embodiment (100), and as can be more clearly seen in Figures 10 to 13, the carriage (106) is configured to include a sensor (110), which in the current embodiment is a microswitch (1 10). The sensor (110) comprises a switch body (120), a lever (1 12) and an activation button (114). The lever (112) is connected to the switch body (120) at one end (118) thereof, and the activation button (1 14) is located between the lever (1 12) and the switch body (120). The lever (112) is made from a resiliently flexible material, allowing it to be bent down towards the button (114) when a force is applied to it. When sufficiently bent towards the switch body (120), the lever (112) will activate the microswitch (1 10). As before, the microswitch (1 10) may be connected to a sensor input of an alarm system, such as a silent alarm, a siren, or the like, either electrically or electronically. Activation of the microswitch (1 10) may accordingly trigger an alarm on the alarm system. In the current embodiment the sensor (1 10) is connected to the alarm system by means of a cable (122). While it is foreseen that wired connections between armed latch plates in accordance with the disclosure and compatible alarm systems may be preferable, it should be noted that alternative, wireless connections such as Bluetooth, wi-fi or similar communication protocols may also be possible.

While in the present embodiment the sensor (110) is positioned on the carriage (106), it should be appreciated that the invention should not be so limited. In alternative embodiments the sensor (110) may be separate from the carriage (106) and instead be positioned on, or otherwise incorporated in, the strike plate (100) or cover (104) wherein the displacement of the carriage (106) will cause it to contact and activate the sensor (1 10).

As mentioned above, the springs (116) may be configured to withstand a threshold force imparted on the barrier without activating the sensor (1 10) in order to avoid accidental alarm activation signals being sent to the alarm system during normal, everyday use and associated environmental conditions. However, the threshold force should be lower than a force at which the barrier, its frame, latch, or strike plate (100) components may be permanently damaged. Normal, everyday use may, for example, include opening and closing the door, weather conditions applying a force on the barrier, slamming the door, and the like. As the springs (1 16) deform, the carriage (106) will be displaced in the direction of the linear force, and eventually, the microswitch (110) will activate by contacting the cover (104) under sufficient force to bend the lever (1 12) to a point where it depresses the activation button (114).

In the present embodiment (100), the linear force applied to the carriage (106) compresses the springs (116). It should be appreciated that other configurations may be possible in which the linear force applies tension on the carriage (106) and springs (116), such that the springs (116) will extend once the applied force is greater than the threshold force. It should be understood that the scope of the invention should not be limited by the type of force exercised on the springs (116). In another example, the springs (1 16) may be torsional springs in which the applied force may exert a torsional force on the springs.

As stated above, it has been found that a sufficient threshold biasing force of the springs (116) referred to in the above embodiments is required to prevent accidental activation of the microswitch (1 10) or sensor, as the case may be, but to ensure activation of the sensor (110) and associated transmission of an alarm signal to the associated alarm system under potential forced entry. In some embodiments, the threshold force may be required to be greater than 250N. More specifically, a threshold force between 300N and 500N may be required to prevent accidental activation at relatively lower forces, but also ensure activation below upper threshold forces at which the barrier or latch mechanisms may be damaged. Preferably, the springs (116) may be biased at a threshold force of between 380N and 41 ON. Even more specifically, the minimum force required to activate the microswitch (1 10), which the biasing springs (1 16) must be able to overcome, may be about 390N. This allows for an attempt to break a barrier open to be noticed before the lock, barrier frame, or any other part of the barrier or lock is broken or otherwise damaged.

A further alternative embodiment (200) of an armed strike plate arrangement in accordance with the disclosure is shown in Figures 14 to 23. In this embodiment the latch may be associated with a sliding barrier such as a sliding door, sliding gate, sliding security gate, or the like. Conventional sliding barrier latch mechanisms include a hook-like latch fixed to the latch portion affixed to the barrier. The hook is typically pivotally mounted within the door-side latch configuration and is configured to hook behind the striker (202), set to the barrier frame, when activated to lock the sliding barrier. The latch mechanism in this embodiment (200) includes a moveable cover (204) and carriage (206), a sensor (208), screws (210), and two springs (212). The carriage (206) is configured to be mounted within the moveable cover (204) and defines sockets within which to accept the springs (212), screws (210) and sensor (208), as shown best in the exploded view of the unit in Figure 19. The sensor described for the purpose of this embodiment (200) is a microswitch (208), as described above. In this embodiment, the hook-like latch (not shown) will enter the catch (216) through its front opening when the sliding door and frame, and accordingly the latch and strike plate sections of the sliding door and frame are adjacent one another, and hooks behind a hook section (214) of the cover (204) when the mechanism is locked. When a linear force is applied in an attempt to open the sliding barrier, such as jerking or pulling the barrier, the hook-like latch will exert a pulling force in the same direction on the hook section (214). The cover (204) will, in turn, impart al force on the carriage (206), which will exert a corresponding, compressive force on the springs (212). Under forces below the threshold force the springs (212) will prevent the microswitch (208) from activating by touching the striker (202), similar to the embodiment described with reference to Figures 14 to 19 above. The microswitch (208) will activate upon forced entry before the cover (204) contacts the striker (202) and, therefore, before any damages to the barrier, barrier frame, latch mechanism, or like occur. The required threshold forces of the springs (212) which will have to be overcome in order to activate the microsensor (208), may be similar to those described above with reference to alternative embodiments of the disclosure. It is, however, foreseen that the threshold force for the sliding barrier configuration may be marginally lower than for the other configurations described above, as forced entry on conventional, swinging barriers may typically be associated with laterally exerted forces on the door, such as a shoulder charge or kick, which are likely to be larger than the pulling forces typically exerted on sliding doors in an attempt to forcefully pull them open.

A still further embodiment (300) of an armed strike plate in accordance with the disclosure is shown in Figures 24 to 31 . As with the embodiment described with reference to Figures 14 to 23, the embodiment of Figures 24 to 31 is configured to be used with a sliding barrier latch mechanism. The strike plate (300) includes an undercut spigot (302) provided for engaging with a latch mechanism of the sliding door by latching onto the undercut neck portion of the spigot (302). The spigot (302) is configured to penetrate (316) a striker (308) and a carriage (306), and connect to a spigot plate (310) on the opposite end of the carriage (306). The spigot (302) is surrounded by a spring (312) situated within the carriage (306). It should be appreciated that one or more springs (312) may be located on any side of the spigot (302). The spring (312) surrounding the spigot (302) should be considered exemplary and not limiting. The carriage (306) further includes a sensor (314). The sensor used for the purpose of this embodiment (300) is a microswitch (314), as described above. The carriage (306) with the microswitch (314), spigot (302), one or more springs (312) and spigot plate (310) are received within a cover (304). The cover (304) is fixed to the striker (308) so as to enclose the spigot (302), microswitch (314), springs (312) and spigot plate (310), as shown in side profile view Figures 28 and 29 and in three- dimensional view in Figures 30 and 31 . When a linear force is applied to open the sliding barrier, such as jerking or pulling the barrier, the spigot (302) will exert a force in the same direction on the spigot plate (310), which will, in turn, exercise an equivalent force on the carriage (306). The carriage (306) will exert a force on the springs (312), and once the springs (312) experience a force large enough to overcome the threshold force, they will deform, in turn moving the microswitch (314) closer to the striker (308). The springs (312) will prevent the microswitch (314) from activating by touching the striker (308) under forces below the thresshold force, similar to the embodiments of Figures 14 and 20 as described above.

The required threshold force of the springs (312) may be similar to the embodiments described above. It is, however, foreseen that the threshold force for the sliding barrier configuration may be less than for the other configurations described above, as forced entry on conventional, swinging barriers may typically be associated with laterally exerted forces on the barrier, such as a shoulder charge or kick, which are likely to be larger than the pulling forces typically exerted on sliding barriers in an attempt to forcefully pull them open.

When the springs (312) deform enough, the microswitch (314) will contact the striker (308) and the alarm signal will be transmitted. It should be appreciated that if displaced even further under the external force, the carriage (306) will ultimately also contact the striker (308) and be held captive behind it. The microswitch (314) will therefore activate upon forced entry before the carriage contacts the striker, and thereby possibly limiting any damages to the barrier, barrier frame, latch mechanism or associated components if the external force is released when the alarm sounds and before the damage takes place.

It will be apparent to those skilled in the art that the mechanisms disclosed provide means through which strike plates of barrier latches can be permanently armed and connected to existing alarm systems. The armed strike plates described allow repeated used without having to be reset are re-armed after activation. Once the external force on the barrier that resulted in activation of the sensor because of it being larger than the threshold biasing force imposed on the carriage has been removed, the carriage will return to its original position under the biasing force and the alarm signal will similarly be removed or otherwise stopped. Once so returned, the activation sensor, button or switch as the case may be, will automatically be depressed and rearmed for the next use. There is therefore no need to manually reset or re-arm the device for subsequent use. It will be appreciated that such a configuration allows the unit to be in an “always-armed” state, thereby alleviating the need to manually set or activate it before each use. The unit is designed to detect excessive forces applied to the barriers to which they are secured, and to not activate during normal, everyday use.

The disclosure also extends to an alarm system including one or more armed strike plates as disclosed fitted to one or more barriers associated with an area or property to be secured. Each armed strike plate may be connected to the alarm system controller of the property or area, thereby enabling the system to detect forced entry through any one of the barriers.

The foregoing description has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure.

The language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by any claims that issue on an application based hereon. Accordingly, the disclosure of the embodiments of the invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.

Finally, throughout the specification and accompanying claims, unless the context requires otherwise, the word ‘comprise’ or variations such as ‘comprises’ or ‘comprising’ will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.