Technical Held. This invention concerns locking arrangements. More particularly, it concerns switch boxes for use with locks in situations where monitoring of a locked door is required. The monitoring may comprise simply a light to indicate that a lock has been applied, or it may be a more complex monitoring arrangement, such as monitoring associated with an alarm system.

Background to the invention. Locks have been in use for many years. Originally, rim locks were developed. A rim lock has a bolt restrained by a tumbler. The tumbler is moved by the action of a key bit, which then engages with a notch on the underside of the bolt so that further rotation of the key causes the bolt to slide until a catch of the tumbler engages with the next notch, on the top of the bolt. To provide improved security, rim locks with several tumblers were developed, and with tumbler notches formed on the inside of a slot. Further security was provided by the use of at least one arcuate ward or arcuate array of studs, fixed to the back plate of the lock around the centre of rotation of the key. The key for the lock then had to be provided with a groove that enabled the key to be rotated with its bit being restrained by the ward or wards. More recently, cylinder locks were developed. In a cylinder lock, a series of spring-biased pin tumblers have to be moved by the key, so that no pin tumbler restrains the rotation of a plug or cylinder into which the key is inserted.

In recent years, organisations that have rooms in which sensitive, classified, secret (including trade secret and top secret) information and/or equipment is stored or d:\docs\add\lockpcts.wpd used, have become aware that (a) special locking arrangements are required to ensure that a door of such a room can be securely locked, and (b) there needs to be some way of monitoring when a door to such a room is no longer locked and the door can be opened. Such monitoring is usually accompanied by a mechanism for generating an alarm signal when the door to the secure area is unlocked - and opened - by an unauthorised person. For this purpose, electrical and electronic circuits have been developed to detect when a lock has been deactivated and/or a door has been opened.

Most companies specialising in the provision of security locking arrangements have developed their own special "end of line" for use with such electrical circuits. The "end of line" is understood to be an assembly of electronic components, so connected together that they provide a signal to a monitoring location when specified events occur, or specified situations exist. (The specified situation will normally include "door locked' and "door unlocked" signals.) Each company that has developed an "end of line" treats its "end of line" as a trade secret, details of which are not to be made public.

Despite the existence of such technology, and the fact that there are a number of monitored security arrangements in use, there is still an unsatisfied demand for a reliable door lock switch box that can be used to house, securely, at least one "end of line" that is used to monitor the state of the door lock. To satisfy this demand, the present inventor developed a box in which a micro-switch and an "end-of-line" of a door locking arrangement for a high security room (a Type 1 secure room) can be mounted. That micro-switch box - which forms an embodiment of the present invention - is constructed to be very strong, and to be mounted within a door frame. Thus the micro-switch box is out of sight and access to it can occur only when the door that is being monitored is open. d:\docs\add\lockpcts.wpd Having designed such a micro-switch box, the present inventor (a) realised that other security applications, including domestic alarm systems, do not require the security criteria for locks for Type 1 secure rooms; and (b) a simpler locking arrangement which costs less to produce, yet still provides good security, would be a useful addition to existing locking arrangements.

Disclosure of the invention. Note: In this specification, including the claims, terms implying a direction or a relative position, such as "top", "bottom", "back", "side", "inwardly", "outwardly", "horizontally" and the like, will be used in the sense that these terms will have when the unit or component being referred to is installed in or on a door frame.

It is an object of the present invention to provide a micro-switch box for use with a lock that includes a retractable bolt. A micro-switch may be mounted within this box in a position such that the micro-switch is actuated when the bolt of the lock is moved to the locking position. Actuation of the micro-switch by the bolt of the lock establishes a signal that shows when the door is locked. This signal may be sent to a monitoring station, that may form part of an alarm system. Preferably, the micro- switch box can be retro-fitted (that is, it can be installed within a door frame in an existing locking arrangement (a) that currently has a non-electronic lock, or (b) as a replacement for existing door lock monitoring equipment).

This objective is achieved by the provision of a micro-switch box which comprises a box having a front wall, a back wall, a top wall, a bottom wall and two side walls, characterised in that (1) a bracket or support plate is provided within the region bounded by said walls, (2) said front wall has an aperture therein through which an end of a bolt of a lock may pass to actuate a micro-switch mounted on d:\docs\add\lockpcts.wpd said bracket.

Normally, said back wall, or said top wall, or said bottom wall, or one of said side walls, will have an aperture therein through which wires to a micro-switch, and to any other electrical or electronic component that may be mounted within said box, may pass.

A striker plate or a cover plate, having an aperture in it through which the end of the bolt of the lock may pass, may form part of the front wall of the box.

Preferably, the dimensions of the box are such that the box may be installed within a door frame.

For specific applications, the box may be constructed in a particular manner.

In one construction, a micro-switch box that is particularly suitable for a simple domestic alarm system (although not limited to such an application) is constructed from a box member that (if the box is made from metal) may be pressed from a blank. In this case, according to a second aspect of the present invention, a micro- switch box comprises a) a box member having a cavity defined by a back wall, a top wall, a bottom wall, two side walls, and a generally rectangular front region which is at least partially open; b) a pair of planar flanges extending outwardly, respectively, from the front edges of said top and bottom walls, the planes of said flanges being substantially co-planar with each other and with said front of said cavity; said flanges each being mountable on said door frame; c) a striker plate or cover plate overlying said flanges; said striker plate d:\docs\add\lockpcts.wpd or cover plate having a region which covers said front of said cavity, with an aperture in said region through which an end of a bolt of a lock of a door mounted on said door frame may pass; and d) a support plate positioned within said cavity; said support plate providing a mounting point for mounting a micro-switch behind said aperture in said striker plate or cover plate so that when said end of said bolt passes through said aperture in said striker plate or cover plate, it contacts the actuating member of said micro-switch to actuate said micro-switch and thereby generate a signal indicating that said door has been locked.

Another use of a micro-switch box is in a security system associated with a lockable bolt. A lockable bolt may be used to lock, for example, a manhole cover or a garage door. In this context, the micro-switch box will usually be mounted on a surface, which (in these examples) will be the surround of the manhole cover or the floor or wall of the garage.

For this situation, the present invention provides a micro-switch box for use with a lockable bolt, said micro-switch box comprising a) a box member comprising a generally planar top wall and two side walls; said top wall having a front edge, a rear edge and two opposed side edges; said side walls extending substantially at right angles to the plane of said top wall from said opposed side edges of said top wall; b) a back wall connected to said rear edge of said top wall and also to rear edges of each of said side walls; c) a front wall connected to said front edge of said top wall and also to front edges of each of said side walls; d) a support plate extending from one of said side walls to the other of said side d:\docs\add\lockpcts.wpd walls, and means for mounting a micro-switch on said support plate; said front wall having an aperture therein through which an end of a bolt of a lockable bolt may pass to actuate a micro-switch mounted on said support plate; and e) means to mount said box member on a surface.

Preferably, the means to mount said box member on a surface comprises a pair of flanges; said flanges extending outwardly from respective bottom edges of said side walls; each of said flanges having at least one aperture therein through which an affixing means (for example, a bolt, an externally threaded stud extending from the surface, a screw or the like) can pass.

In another construction, that is particularly suitable for a more complex domestic alarm system (although not limited to such an application), a further aspect of the present invention provides a micro-switch box which comprises: a) a box member having a size such that it can be fitted into the frame of a door, and having a cavity defined by (1) a generally planar back wall, from the upper and lower ends of which, respectively, a top wall and a bottom wall extend substantially at right angles to the plane of said back wall; said top and bottom walls extending from said back wall to a generally rectangular front wall which is formed as a pair of planar sub-walls (or flanges) which extend towards each other from the ends of the top and bottom walls which are remote from said back wall; the planes of said sub- walls (or flanges) being (a) substantially co-planar with each other and (b) parallel to the plane of said back wall; the proximate ends of said sub- walls being spaced from each other to form a gap in said front wall between said proximate ends of said sub- walls; said back wall, top d \docs\add\lockpcts wpd wall, bottom wall and sub- walls having substantially equal widths; (2) a substantially rectangular first side wall, the edges of which are at respective side edges of said back wall, top wall, bottom wall, said sub- walls, and said gap between said sub- walls; and (3) a substantially rectangular, separate, side wall plate having dimensions such that its side edges may overlie the other respective side edges of said back wall, said top wall, said bottom wall, said pair of flanges, and said gap between said sub- walls; b) a plurality of (typically four) spaced apart cylindrical studs; each stud having an elongate dimension and extending from said first side wall, with said elongate dimension perpendicular to said first side wall, into said cavity for a distance equal to or slightly less than the width of said top wall, said bottom wall, said back wall and said sub-walls; each of said studs having a central bore which is internally threaded; c) a plurality of apertures in said side wall plate, said plurality of apertures being equal in number to, and in locations corresponding to the positions of, said plurality of studs, whereby screws inserted into said apertures and engaging with the internal threads of said bores of said studs, on tightening, securely mount said side wall plate in position as a second side wall of said cavity; and d) a support plate extending between said top wall and said bottom wall, said support plate having an aperture therein to enable a plunger type micro-switch to be mounted on said support plate with its plunger positioned behind said gap between the ends of said sub- walls.

A lever type micro-switch may be mounted on said top, bottom or back wall, or on said support plate, with its lever slightly proud of the plane containing the edges of the top, bottom and back walls which are remote from said first side wall, to provide a signal when the side wall plate is screwed into position and depresses the lever. d:\docs\add\lockpcts.wpd An "end of line" may be mounted (positioned) within the space between the plunger type micro-switch (mounted on the support plate) and the back wall. Typically, the end of line will be mounted on the support plate.

Apertures in the flanges that form the (partially open) front of the box will usually be provided to facilitate the mounting of a striker plate or cover plate on the flanges (the striker plate or cover plate being used to mount the micro-switch box on the frame of a door, preferably with the box of the micro-switch box within the cavity of the wall which is alongside the door frame).

The signal generated by the plunger type micro-switch (and also the signal generated by the lever-type micro-switch, if present) may be registered or recorded at a remote monitoring station.

An optional feature in each of the two micro-switch boxes for use in domestic alarm systems which have been outlined above, is a magnetically activated, balanced reed switch, mounted in the cavity of the micro-switch box, adjacent to the front wall of the micro-switch box. This reed switch, when activated by the presence of a magnet or a ferromagnetic material mounted on the edge of the door that is hung on the door frame in which the micro-switch box is mounted, will provide an additional signal and/or an audible sound (usually monitored at a remote monitoring station), which indicates that the door has been closed, but is not necessarily locked.

Another aspect of the present invention is the provision of a micro-switch box that is suitable for use with doors of a Type 1 secure room (that is, a room in a facility which handles top secret material), although not limited to such an application.

d:\docs\add\lockpcts.wpd According to this aspect of the present invention, a micro-switch box comprises: a) a length of a steel tube, the cross-section of which is essentially an elongate rectangle having two opposed shorter sides and two opposed longer sides, whereby said length of steel tube has two opposed side faces of smaller width and two opposed side faces of larger width; one of two opposed side faces of smaller width forming a back wall of the micro-switch box; the other of said two opposed side faces of smaller width having a portion thereof removed and forming a front wall of said micro-switch box; said two side faces of larger width forming side walls of said micro-switch box; b) two elongate, planar, essentially rectangular, steel plates having dimensions such that said two plates are a snug fit within said tube at the top and bottom ends of said side walls; said two rectangular plates forming, respectively, a top wall and a bottom wall of said micro-switch box; at least one of said two rectangular plates having a pair of flanges extending one from each end thereof at right angles to the plane of the rectangular plate; each of said flanges each having at least one threaded aperture therein for receiving a screw which has passed through an aperture in said front wall or said back wall, to hold that rectangular plate in position as the top wall or the bottom wall of said micro-switch box; c) a striker plate or cover plate overlying said front wall; said striker plate or cover plate having a region which covers said removed portion of said front wall and an aperture in said region through which an end of a bolt of a lock of a door mounted on said frame may pass; and d) a support plate mounted on one of said side walls, within said micro-switch box; said support plate providing a mounting point whereby a plunger type micro-switch may be mounted with the plunger of the micro-switch behind the aperture in said striker plate or cover plate.

d:\docs\add\lockpcts.wpd An "end of line" may be mounted (positioned) on the support plate or within the space between the support plate and the back wall of the micro-switch box.

Preferably, a lever type micro-switch is mounted on one of said side walls, or on the support plate, with its lever positioned so that when said top or bottom wall which has associated flanges is mounted to close the micro-switch box, it depresses the lever of the micro-switch, to provide a signal which shows that the micro-switch box has been closed. (If both the top wall and the bottom wall have associated flanges, a respective lever type micro-switch should be mounted at the top and at the bottom of a side wall.)

In all constructions of the micro-switch box, the signal generated by the micro-switch which is mounted on the support plate in the micro-switch box may be registered or recorded at a remote monitoring station.

These and other features will be further illustrated in the following description of embodiments of the invention, which are examples only of implementations of the invention. In the following description, reference will be made to the accompanying drawings.

Brief description of the drawings. Figure 1 shows, in outline, a slim micro-switch box constructed in accordance with the present invention, installed within a door frame.

Figure 2 is a partly schematic perspective sketch of a micro-switch box which is constructed in accordance with the present invention.

Figure 3 shows (partly schematically) a door locking arrangement which includes a d:\docs\add\lockpcts.wpd micro-switch box similar to that shown in Figure 1 , but with a plunger type micro- switch and with the inclusion of a reed switch to provide a "door closed" signal.

Figure 4 shows the shape of a blank which may be used to form the box of the micro-switch box illustrated in Figure 2 and Figure 3.

Figure 5 illustrates a micro-switch box that is used with a lockable bolt (for example, in the security system of a garage door).

Figure 6 is a partly schematic perspective sketch of another embodiment of a micro-switch box, which is also constructed in accordance with the present invention.

Figure 7 shows the shape of a "blank" that may be used in the construction of the micro-switch box shown in Figure 6.

Figure 8 is a partly schematic exploded view of the preferred form of a micro- switch box constructed in accordance with the present invention, for use in top secret areas.

Detailed description of the illustrated embodiments. Figure 1 shows a door frame 10 within which a door 11 is hung on hinges (not shown). The door 11 is opened and closed using handles 12. An associated lock in the door has a bolt 13 (shown projecting from the edge of the door although, in practice, the bolt will be retracted when, as shown in Figure 1 , the door is not wholly within the door frame 10, but is "open").

A micro switch box 14 (shown in dashed outline) is mounted, within the door frame d:\docs\add\lockpcts.wpd 10, on a cover plate 15 which is flush with the surface of the door frame 10. Screws 16 hold the cover plate 15 in position in the door frame 10. The body of the switch box 14 is secured to the cover plate 15 by screws 17, which engage with respective flange members, shown in Figures 2, 3, 6 and 8.

The micro-switch box shown in Figure 2 has a cavity 100 formed by a top wall 101, a bottom wall 102, a back wall 103 and two side walls 104 (one of which is shown only partially in Figure 1). This cavity has a rectangular open front, from two sides of which respective flanges 105 extend. The flanges 105 are co-planar with the front of the cavity 100, and extend outwardly from the front ends of the end walls 101 and 102.

The walls defining the cavity and the flanges 105 may be pressed from a single blank of steel, an aluminium alloy, or any other suitable metal having the shape shown in Figure 4. Alternatively, they may be formed using a rigid plastics material (for example, a polycarbonate material). One, or both, of the flanges 105 may extend across the front of the micro-switch box to close, partially, the front of the cavity 100. Such an extension of the flanges 105 across part of the front of the cavity can be achieved (a) by appropriate moulding or folding, if the walls defining the cavity and the flanges 105 are constructed using a plastics material, or, (b) if the walls defining the cavity and the flanges 105 are made from a metal blank, by a double folding of an elongate blank member 105 of the blank shown in Figure 4.

A support plate 107 extends from one side wall 104 to the other side wall. A lever type micro-switch 108 (for example, a lever micro-switch type SS-5GL) is mounted on the support plate 107. Leads 109 from the micro-switch 108 pass through an aperture 115 in the back wall 103 of the micro-switch box. Hence, when the switch box is mounted on a door frame (that is, when it is installed, in effect, within the d:\docs\add\lockpcts.wpd wall in which the associated door frame is positioned), the leads 109 from the micro- switch 108 can be run through a conduit 116 which is located out of sight, in the wall cavity, so that it is not possible to tamper with these leads, and the security of the door lock monitoring arrangement is further improved.

When the switch box is to be installed in a door frame, the cover plate or a striker plate 110 is mounted over the front of the micro-switch box and covers the flanges 105. (A striker plate 110 is shown in Figure 2; if the tongue 112 of the striker plate is not present, it would be a cover plate.) To install (mount) the micro-switch box in a door frame, screws 117 are passed through respective counter-sunk apertures 114 in the striker plate 110, and through respective apertures 113 in the flanges 105, and are screwed into the door frame. Normally, the region where the micro-switch box is to be mounted will have been recessed so that the outer surface of the striker plate 110 is essentially flush with the surface of the door frame.

The striker plate 110 has an aperture 111 into which the end of a bolt 119 (being the bolt of the lock of the door that is supported by the door frame) will enter when the door has been closed and is locked. As the end of the bolt 119 of the lock moves into the cavity 100 of the micro-switch box, it first comes into contact with, then depresses, the lever 118 of the micro-switch 108 (or the plunger of the micro- switch if a plunger type micro-switch is used instead of a lever type micro-switch). Movement of the lever 118 (or the plunger) actuates the micro-switch, closing a circuit and providing a signal, which indicates that the door is locked.

This signal resulting from the actuation of the micro-switch 108 may be used to provide a local indication that the door is locked. For example, in a school or other institution that has a number of doors opening from respective rooms into a corridor, an array of light emitting diodes (or an alternative light emitting arrangement) d:\docs\add\lockpcts.wpd may be positioned in the corridor, above (or alongside) each of the doors. When each door is locked, the signal generated by the activation of the micro-switch is used to illuminate its associated LED array (or to change the colour of the associated LED array if two such arrays are mounted above, or alongside, each door). A caretaker or a security officer, on entering the corridor and observing the LED arrays, can see, immediately, whether each of the doors has been locked.

Alternatively, or in addition, the signal indicating that the door is locked may be used, in conjunction with other devices (for example, a key pad into which a correct code number must be entered within a prescribed time - typically 30 seconds - when the door is unlocked and the micro-switch is de-actuated) as part of an alarm system.

In some instances (for example, in a storage facility for goods that are being sold), it is convenient to know that a door is closed at certain times (for example, during working hours) but not necessarily locked, and for an alerting signal to be generated when the (unlocked) door is opened. A modified form of the present invention can be used to provide such an alerting signal. An example of such a modified arrangement is shown in Figure 3.

In the locking arrangement illustrated in Figure 3, the support plate 107 extends from the top wall 101 to the bottom wall 102 of the micro-switch box. A plunger type micro-switch 125 (for example, a 6PL4 type plunger micro-switch marketed by Farnell Pty Ltd of Sydney, Australia, as panel mounting plunger 103-479) is mounted on this support plate, with the plunger 126 of the micro-switch behind the aperture 111 of the striker plate or cover plate 110. A balanced reed switch 120 is also mounted within the cavity 100 of the micro-switch box, on the support plate 107. A magnet (or a ferromagnetic rod, plate or bar) 121 is mounted on the edge d :\docs\add\lockpcts. wpd of the door 122, within, or close to, the lock 123 of the door which contains the bolt 119. When the door is closed, the magnet (or ferromagnetic material) 121 is positioned closely adjacent to the reed switch 120, and activates it. The electrical connection between the reed switch 120 and a remote monitoring station is also through the aperture 115 in the back wall 103, then via the conduit 116 in the wall cavity behind the door frame, and thus is another tamper-proof connection. (It should be noted that the aperture 115 need not be in the back wall 103; it could be in the top wall 101 or in the bottom wall 102, or in one of the side walls 104.) As shown in Figure 3, a single conduit, or a single multi-stranded cable, may be used to provide the electrical connections from both the micro-switch 125 and the reed switch 120 to the remote monitoring station. However, when more than one device with electrical connections is included in the micro-switch box, the connection to each device may be via separate cables, entering through different apertures in one or more of the back wall, the top wall, the bottom wall and the side walls.

An audio alarm may be included in the monitoring system associated with a micro- switch box equipped with a reed switch, to provide an audible signal when the door has been open for more than a pre-determined time.

Typically, the micro-switch box will be a slim box, having a width of about 25 mm, but other widths of the micro-switch box may be used, to suit particular applications of the invention.

The striker plate (or cover plate) 110 shown in Figures 2 and 3 of the drawings, and the cover plate 15 of Figure 1, is an elongate plate having a length and width that is sufficient to just cover the flanges 105. In some implementations of the invention, the striker or cover plate 110 may have a greater width, in which case additional apertures may be included in the cover or striker plate 110 to receive additional d:\docs\add\lockpcts.wpd screws to hold the cover plate 110 in position on the door frame.

The aperture 111 in the cover or face plate 110 shown in Figures 2 and 3 of the drawings, and the aperture 18 of Figure 1 , is depicted as a rectangular aperture, because the bolt 119 (bolt 13 in Figure 1) has a substantially rectangular cross- section. Preferably, the aperture 111 (and aperture 18) will have a shape that corresponds to the cross-sectional shape of the end of the lock bolt 119 (bolt 13 in Figure 1) that will pass through it, which need not be rectangular. It is also preferred that there is only a small clearance between the outer surface of the lock bolt 119 (13) and the periphery of the aperture 111 (18).

Reinforcing members may be included in the box of the micro-switch box, as required.

As noted above, another use of a micro-switch box is in a security system associated with a lockable bolt. A lockable bolt may be used to lock, for example, a manhole cover or a garage door. In this context, the micro-switch box will usually be mounted on a surface, which (in these examples) will be the surround of the manhole cover or the floor or wall of the garage.

An embodiment of a micro-switch box for use with a lockable bolt is shown in Figure 5. This micro-switch box comprises a length / of a metal box member 130 of uniform cross-section, this cross-section comprising an inverted U-shape (Fl) with outward horizontal extensions at the lower ends of each arm of the inverted U. Since this micro-switch box is likely to be in an exposed position, the box member is preferably of strong stainless steel.

The box member 130 provides a top wall 136 and two side walls 137 of the micro- d:\docs\add\lockpcts.wpd switch box. The box member 130 is secured in position by bolts which pass through bolt holes 131 in the two horizontal extensions 135 of the box member. The rear of the box member is closed by a back wall 132, which preferably comprises a stainless steel panel that is seam welded to the box member. The front of the box member 130 is closed by a second panel 133 - a front wall - which contains an aperture 134 that has dimensions which enable the end of the bolt of the lockable bolt to pass through it. A micro-switch (preferably a plunger type micro-switch) is mounted on a support plate (not shown) in the cavity formed by top wall 136, the back wall 132, the side walls 137 and the front wall 133 of the box member 130. When the manhole cover, garage door or the like is locked, the end of the lockable bolt enters the aperture 134 and bears against, then depresses, the plunger of the micro-switch. Actuation of the micro-switch causes a signal to be generated that provides an indication that the garage door or the like is locked.

When a lockable bolt is used with a garage door, it is possible for the lockable bolt to vary in position relative to the micro-switch box when the garage door is closed. Thus the aperture 134 must be sufficiently large to receive the end of the bolt in whatever position the bolt is located when the garage door has been closed. This means that it is possible that the end of the bolt, when entering the aperture 134, may not always bear against the plunger of the micro-switch, but may move to a position alongside that plunger. To avoid this possibility, a cap containing a disc may be mounted on top of the plunger of the micro-switch, with the disc extending sideways from the plunger. With this arrangement, the end of the bolt, when it is passed through the aperture 134, will always bear against the disc, then move the disc and thus the cap (and with it the plunger of the micro-switch) as the bolt of the lockable bolt is moved into its locking position.

The micro-switch box shown in Figure 6 has a back wall 201. From the upper and d:\docs\add\lockpcts.wpd lower ends of this back wall 201, a top wall 202 and a bottom wall 203 extend horizontally. The walls 201 , 202 and 203 have the same width. A substantially rectangular side wall 204 has three of its edges at side edges of the back, top and bottom walls. A pair of flanges or sub-walls 205 and 206 extend towards each other from, respectively, the end of the top wall 202 which is remote from the back wall 201 and the end of the bottom wall 203 which is remote from the back wall 201. These sub-walls 205, 206 are co-planar with each other and each sub- wall has one of its edges at an edge of the side wall 204.

Conveniently, the box comprising the walls 201, 202, 203 and 204, and the sub- walls 205 and 206, can be constructed by (a) being pressed (punched) from a steel "blank" having the shape shown in Figure 7, and then (b) seam welding the adjacent ends of the walls 201 and 202; 201 and 203; 202 and 205; and 203 and 205.

Four cylindrical studs 208, each with a threaded bore 228, are mounted (by known means) on the side wall 204, near the corners of this side wall. Each stud has an elongate axis (although the studs need not have a circular cross-section) which is perpendicular to the plane of the side wall 204. A rectangular side wall plate 207 has dimensions such that its edges overlie the edges of the back wall 201, the top wall 202 and the bottom wall 203, and also the edges of the flanges 205 and 206, which are remote from the side wall 204. The side wall plate 207 is preferably of steel which has been laser cut to size. Apertures 210 in the side wall plate are positioned to correspond with the bores 228 of the studs 208, and are countersunk. Screws 209, when passed through respective apertures 210 to engage with the threads of the bores of the studs 208, are tightened to ensure that the side wall plate 207 is clamped firmly over the edges of the walls 201, 202 and 203, and preferably also over the edges of the sub-walls 205 and 206.

d:\docs\add\lockpcts.wpd For the strongest micro-switch box construction, each stud 208 should have a length which is such that the end of the stud that is remote from the side wall 204 is co- planar with the edges of the walls 201 , 202 and 203 and also with the edges of the sub- walls 205 and 206. This length of each stud 208, therefore, is preferred. However, studs 208 which are shorter than this preferred length may be used.

If access to the micro-switch box after its installation in a locking arrangement is unlikely to be required on a regular basis, as few as two studs 208 may be used to hold the side wall plate 207 in position over the edges of the back wall 201, the top wall 202 and the bottom wall 203, and also over the edges of the sub walls 205 and 206, which are remote from the side wall 204. However, in practice, the minimum number of studs 208 that are likely to be used will be three. Four studs 208, as shown in Figure 6, is the preferred number of studs, although six studs 208, with three studs spaced apart near to the top wall 202 and with three studs spaced apart near to the bottom wall 203, will be preferable if the number and size of the components to be included in the micro-switch box are such that there is a significant distance between the sub- walls 205, 206 and the back wall 201.

A cover plate 213 (which, in some realisations of this form of the invention, may be a striker plate) is shown affixed to the micro-switch box of Figure 1. The cover plate 213 is mounted on the sub walls 205 and 206 using short screws 219. Apertures 215 in the end regions of the cover plate enable it (and with it, the micro- switch box) to be mounted on a door frame, using screws of a suitable size. The cover plate 213 has an aperture 214 in it which, when the face plate is mounted on a door frame, is penetrated by the end of the bolt of the door lock when the door is locked.

A support plate 220 is mounted within the micro-switch box. The support plate 220 d :\docs\add\lockpcts. wpd (which, preferably, (a) is of steel, and (b) has a width which is the same as the width of the walls 201, 202 and 203) extends from the inside face of the top wall 202 to the inside face of the bottom wall 203. The support plate 220 is preferably a planar plate with its plane at right angles to the planes of the top and bottom walls, and parallel to the plane of the back wall 201.

An aperture in the support plate 220 enables a plunger type micro-switch 211 to be mounted on the support plate 220 with its plunger 212 behind the aperture 214 of the cover plate. When the door with which the micro-switch is associated is locked, the end of the bolt of the door lock passes through the aperture 214, then bears against and depresses the plunger 212 to actuate the micro-switch 211. Actuation of the micro-switch closes a circuit and provides a signal which indicates that the door is locked.

A lever-type micro-switch 216 is included in the embodiment illustrated in Figure 6. The lever type micro-switch is shown mounted on the top wall 202. However, the lever type micro-switch may be mounted, instead, in any other suitable position (for example, on the back wall 201 or on the bottom wall 203, or on the support plate 220). Whichever mounting position is chosen, the free end of the lever 217 of the micro-switch 216 should project above the plane defined by the edges of the walls 201, 202 and 203 which are remote from the side wall 204. Thus, when the side wall plate 207 is screwed into position, the inner face of the side wall plate will bear against the lever 207 to actuate the micro-switch 216. When, subsequently, the side wall plate 207 is removed from the micro-switch box, the lever 217 will be released and a change in the signal indicating the state of the micro-switch 216 will occur, and will be monitored by a security surveillance system associated with the micro-switch box.

d :\docs\add\lockpcts. wpd An "end of line" can be inserted into the micro-switch box in the space between the plunger type micro-switch 211 and the back wall 201. Such an "end of line" may be mounted on the support plate 220.

Optionally, a balanced reed switch may be included in the micro-switch box, in the space between one of the flanges or sub-walls 205 or 206 and its closest stud 208. Such a reed switch - which may also be mounted on the support plate 220 - will function in the same manner as the reed switch that is included in the embodiment illustrated in Figure 3, described above.

The embodiments of the present invention that have been illustrated in Figures 2, 3 and 6 may not meet the criteria for use in Type 1 secure room applications. However, they may be installed in a wide range of monitoring equipments (in addition to the corridor application mentioned above), including domestic, office and warehouse monitoring and alarm systems, and (provided the micro-switch box is made of heavy duty steel) in custodial establishments (for example, in a police or prison cell, in a remand home, or the like). They may be used with any conventional lock having a bolt, whether a rim lock or a cylinder lock. They may also be used in a freezer, provided that the micro-switch (and also the reed switch, if the reed switch is included) is rated for operation at temperatures down to -20C. These applications of the invention are not exhaustive.

A particular benefit of the micro-switch box shown in Figure 6 is that the use of a side wall plate for access to the interior of the micro-switch box enables the micro- switch box to be constructed so that it has a width that is only slightly greater than the width of the plunger type micro-switch 211. Therefore it is possible to manufacture a very thin micro-switch box, which is suitable for retro-fitting into door frames in partitioning walls (which are significantly thinner than a standard d:\docs\add\lockpcts.wpd stud wall).

A micro-switch box that is suitable for use in a Type 1 secure room is illustrated in Figure 8. The construction of the micro-switch box shown in Figure 8 meets the specification for installed components in top secret areas (that is, areas where only personnel with a top secret security classification are permitted to have access).

The switch box of the Figure 8 embodiment has side walls 321 and 323, a back wall 322 and a front wall 324 formed integrally from a length / of a steel tube having a generally rectangular cross-section. Preferably, the steel of this tube is 1.8 mm thick. The front wall 324 has a portion 325 removed, thus providing two front wall regions 326 and 327, separated by a gap or aperture 325.

The top wall 302 of the micro-switch box is a planar rectangular piece of steel, also (preferably) 1.8 mm thick, which is seam welded to the adjacent top edges of the side walls 321 and 323, to the top edge of the front wall region 326 and to the top edge of the back wall 322. For an installation in a situation where the security requirement is less than top secret, the steel thickness may be less than 1.8 mm, and the top wall 302 may be attached to the adjacent wall edges by spot welds, or in the same manner as the bottom wall 303 of the micro-switch box is attached (see below).

The bottom wall 303 is a generally planar part of a steel bottom wall member having flanges 304 and 305 extending orthogonally, in the same direction, from each end of the bottom wall 303. The dimensions of this bottom wall member are such that the flanges 304 and 305 are a close fit inside the switch box, with the flange 304 adjacent to the inside face of the front wall 327 and with the flange 305 adjacent to the inside face of the back wall 322. The flanges 304 and 305 have threaded d:\docs\add\lockpcts.wpd apertures 334 which, when the end wall 303 is positioned correctly to assemble the box, are aligned with countersunk apertures 333 in the front and back walls, through which respective screws 317 pass. Each of the screws 317 engages with the internal thread of a respective aperture 334 in the flanges 304 and 305, to hold (when the screws 317 are tightened) the bottom wall 303 securely in position.

A cover plate 315 (which, alternatively, may be a striker plate) fits over the front wall 324 of the micro-switch box. The cover plate 315 has an aperture 318 which, when the cover plate is attached to the box, is aligned with the gap or aperture 325 of the front wall, and through which the end of the bolt of the lock of the door which is associated with the micro-switch box can pass when the micro-switch box is mounted on the associated door frame.

The cover plate 315 also has countersunk apertures 319 above and below the aperture 318. The distance between the centres of the apertures 319 is equal to the distance between the centres of the apertures 333 in the front wall regions 326 and 327. Thus a screw 320 and one of the screws 317 can be used to attach the cover plate 315 securely to the front wall of the micro-switch box. Two additional apertures 306 are provided in the cover plate 315, so that screws 316, passing through respective apertures 306, may be used to attach the cover plate 315, and with it the micro-switch box, to a door frame, with the micro-switch box positioned within the cavity of the wall behind the door frame.

A support plate 339, with an integrally formed mounting flange 327, is mounted within the box, using screws (not shown) which pass through apertures 340 in the side wall 323 and engage with the threaded apertures 329 in the mounting flange 327. A piece of steel angle, approximately equal in length to the top-to-bottom dimension / of the side walls 321 and 323 is a convenient item which provides both d:\docs\add\lockpcts.wpd the support plate 339 and the flange 327. The planar upper surface of the support plate 339 is parallel to the elongate direction of the back wall 322.

A plunger micro-switch 340 (typically, as noted earlier in this specification, a 6PL4 type plunger micro-switch marketed by Farnell Pty Ltd of Sydney, Australia, as a panel mounting plunger 103-479) is mounted on the support plate 339 with its plunger 341 above the support plate 339. When the support plate is mounted in position in the micro-switch box, (a) the plunger 341 is aligned with the apertures 325 and 318, so that the end of the lock bolt, when it passes through the apertures 318 and 325, will bear against, and depress, the plunger 341; and (b) a cavity is formed between the support plate 339 and the back wall 322, within which the body of the plunger micro-switch 340 is located, and within which at least one "end of line" may be positioned.

As in the case of the embodiments illustrated in Figures 2, 3 and 6, when the plunger micro-switch 340 is actuated by the depression of the plunger as the end of the lock bolt passes through the aperture 318 in the cover plate and the gap or aperture 325 in the front wall, the micro-switch (in a typical installation) generates a signal that informs a monitoring or control installation that the door associated with the micro- switch box has been locked. When the door is unlocked, and the end of the lock bolt is withdrawn from the micro-switch box, the plunger 341 moves to its original position and a different signal is seen at the monitoring or control installation.

A second micro-switch 342, which is a lever type micro-switch (for example, the Lever Arm Mini Micro-switch marketed by Farnell Pty Ltd of Sydney, Australia), is mounted on the side wall 321 using nuts and bolts 344 and 345, in conjunction with apertures 331 in the side wall 321 and the standard mounting apertures in the d:\docs\add\lockpcts.wpd body of the lever type micro-switch 342. The mounting of the lever type micro- switch 342 is such that its spring-biased lever arm 343 is depressed when the end wall 303 is secured in position. If the end wall 303 is subsequently removed from the switch box, the lever arm 343 moves to open the micro-switch 342. This change of switch position is used to generate a tamper alarm signal at a monitoring station or installation.

The embodiment illustrated in Figure 8 was conceived for use by organisations which have areas that need very high security. However, as noted above, this embodiment of the invention is not limited to such applications. In fact, it is suitable for use in alarm systems in factories, shops and houses, and it may be used in safes and strong boxes if remote monitoring of such storages is required. These applications of this embodiment of the invention are not exhaustive.

It should be appreciated that preferred embodiments of the invention have been illustrated in Figures 2, 3, 6 and 8 of the accompanying drawings, and that those embodiments - and similar embodiments - may be constructed using different box assemblies and with different support plate constructions located in different positions within the box of the micro-switch box.

It should also be appreciated that, although a planar support plate has been shown in Figures 2, 3, 6 and 8 of the accompanying drawings, the support plate need not be planar. It may be an arcuate plate, or a stepped plate, or any other shape which can be mounted within the box of the micro-switch box and support a micro-switch in the required position (and also support any other electrical or electronic component that may have to be included in the micro-switch box). In addition, with the possible exception of a micro-switch box for use in a type 1 secure room, the side walls, top wall, bottom wall and/or back wall of the micro-switch box need not d:\docs\add\lockpcts.wpd be solid walls. These walls may be provided with venting apertures (particularly if a heat generating component may be mounted within the micro-switch box) or they may be constructed from a rigid open or close mesh material.

The embodiments of the invention which are illustrated in Figures 2, 3, 6 and 8 of the accompanying drawings are all slim micro-switch boxes, constructed so that they can be fitted into existing door frames as a retrofitted update of the security of a door locking arrangement, with the box of the micro-switch box hidden from view by being located in the cavity of the wall in which the door frame is mounted. For specific applications, a slim switch box may not be required, and might be inappropriate in view of the electronic components to be mounted within the micro-switch box.

Locksmiths and security experts will appreciate that examples only of realisations of the invention have been described in this specification, and that variations in or modifications to the construction of the micro-switch box may be made without departing from the present inventive concept, as set out in the claims.

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