Abstract:
A door chain assembly comprising a chain and an anchor plate. The anchor plate comprises a back plate and a chain-receiving plate and the chain-receiving plate extends from the back plate. The chain-receiving plate is provided with an aperture and/or a chain-holding slot. The chain comprises a plurality of links with adjacent links being rotationally offset with respect to one another.

Description:
[0001]    This application claims priority to United Kingdom Patent Application No. 1516028.6 filed on Sep. 10, 2015 which is hereby incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The invention relates to door looking device that restrict the level to which a door can be opened, particularly for use with front doors to buildings. 
       BACKGROUND TO THE INVENTION 
       [0003]    Door locking devices, which allow secure limited opening of a door for permitted inspection of a caller but prevent unwanted entry, are generally referred to as “door chains”. These devices usually comprise a short length of chain; a first end of which is secured to a door frame the second end of the chain is releasably secured to a guard plate, with the guard plate being fixedly attached to a door associated with the door frame. When the second end of the chain engages the guard plate, the door chain allows the door to be opened a small amount to confirm the identity of the caller, but prevents unwanted entry, after inspecting the caller, the second end of the chain may be disengaged from the door guard plate allowing the door to be opened fully. 
         [0004]    There are shortfalls associated with the most commonly used, conventional door chains of this type. For example, the door chains:
       1) do not provide for varying degrees of limited opening of a door;   2) they do not provide adequate protection for the edge of the door against damage caused by contact with the chain; and   3) the chain may to inadvertently disengage the door guard plate when the door vibrates as it is kicked violently by a would-be intruder, thereby compromising security.       
 
       SUMMARY OF THE INVENTION 
       [0008]    Accordingly, the present invention is directed to a door chain assembly comprising a chain and a guard plate, wherein: 
         [0009]    the guard plate comprises a back plate and a chain-receiving plate, wherein the chain-receiving plate extends from the back plate and the chain-receiving plate is provided with an aperture and/or a chain-holding slot; 
         [0010]    and wherein the chain comprises a plurality of links with adjacent links being rotationally offset with respect to one another. 
         [0011]    The present invention positions the chain-receiving aperture and/or slot in a position that is non-parallel with the door. As a result, when the chain engages the aperture and/or slot of the guard plate, gravity assists with seating the chain within the aperture and/or slot. Thus, it becomes more difficult for the chain to inadvertently disengage because to do so, the chain has to move away from the floor, rather than simply away from a vertical slot. 
         [0012]    Preferably, the chain receiving plate extends away from the back plate at an angle between 45° and 135° from the back plate and, more preferably, the chain-receiving plate extends substantially perpendicularly from the back plate. Again, by positioning the slot to be non-parallel with the door, and preferably substantially parallel with the ground, the likelihood of the chain inadvertently disengaging is reduced. 
         [0013]    Advantageously, the aperture and/or the chain-holding slot is provided with removable blocking means and, more advantageously, the removable blocking means is connected to the guard plate and is able to be temporarily displaced from the aperture and/or the chain-holding slot. By providing blocking means that can be inserted and removed from the chain-holding aperture and/or slot, the chain can be prevented from being unintentionally removed from the chain-holding slot. 
         [0014]    In a preferable arrangement, the blocking means is biased so that in a rest position it extends at least partially into the aperture and/or the chain-holding slot and it can be at least partially temporarily displaced against the bias to reduce the amount it extends into the aperture and/or the chain-holding slot. Providing bias means, the blocking member has to be actively retracted to engage or disengage the chain. As a result, the chain cannot be inadvertently disengaged, thereby resulting in a more secure arrangement, particularly as the chain is also arranged to be held in the aperture and/or slot by gravity. 
         [0015]    In one arrangement, the aperture is in communication with a second slot extending in a different direction from the chain-holding slot and the blocking means engages the second slot and biasing means comprises a compression spring positioned in or adjacent to the second slot to resist movement of the blocking means from the aperture and/or the chain-holding slot. A second slot may be provided to hold the biasing means for the blocking member. This allows for the use of a compression spring, or similar, to be employed to bias the blocking member in a position wherein it blocks the aperture and/or slot. 
         [0016]    Advantageously, the blocking member comprises a pivotable cap that is adapted to be received within the aperture. The cap may be connected to the guard plate or the back plate and is able to pivot into, and out of, the aperture and/or slot, thereby blocking the chain from engaging or disengaging the guard plate. 
         [0017]    Alternatively, the blocking member comprises a spring member attached to the guard plate, which, in a rest position, extends into the aperture and/or the chain-holding slot and is adapted to be temporarily displaced such that, when in the displaced position, it is clear of the aperture and/or the chain-holding slot. The use of a spring member provided a biasing to the device, which then allows the aperture and/or slot to be blocked and unblocked as required. 
         [0018]    It may be desirable that the chain-holding slot comprises at least one angled section. By providing an angle in the chain-holding slot, for example the slot being “V” or “W” shaped, the channel in which the chain is held becomes more complex and makes inadvertent disengaging more difficult. Whilst the slot might be provided with curves, an angle is more difficult for the chain to traverse. 
         [0019]    It is advantageous that the longitudinal axis of the links of the chain are substantially perpendicular to one another. Having the links of the chain arranged to be substantially perpendicular to one another allows for the length of the chain to be adjusted by feeding a link into the chain-holding slot in a particular orientation, wherein the adjacent links cannot pass through the chain-holding slot due to their orientation. 
         [0020]    The assembly may be provided with a chain anchor plate, which is fixedly attached to a door frame for securing one end of the chain to the door frame. Alternatively, the chain may be connected directly to the door frame. 
         [0021]    Preferably, the arrangement between the guard plate and the back plate forms what may be described as a ‘T’ bar as, when viewed from its end, it is generally in the form of a ‘T’ shaped elongate bracket in which the guard chain is engaged in the substantially horizontal limb of the door guard plate. 
         [0022]    The central rib of the ‘T’ bar or ‘T’ shaped bracket may define an aperture close to one end and centrally therein, from which a pair of opposing long narrow slots respectively, extend outwardly from the aperture centrally and transversely of the central rib to slot ends adjacent each end of the central rib. Alternatively, a keyhole shaped aperture may be provided in the central rib of the ‘T’ bar with the keyhole aperture adjacent one end of the central rib and a long narrow slot leading from the aperture, centrally of the central rib to a slot end adjacent the other end of the central rib of the ‘T’ bar door guard plate. 
         [0023]    The slot in the device may be a closed slot, that is, a slot that has a close periphery. 
         [0024]    The back plate may be integral with the guard plate or they may be separate parts that are fixedly connected to one another. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    The invention will now be described further by way of example, with reference to the accompanying drawings, in which: 
           [0026]      FIG. 1  is a front view of a door chain assembly in accordance with the present invention; 
           [0027]      FIG. 2  is a perspective view of the assembly of  FIG. 1  in a first position; 
           [0028]      FIG. 3  is a top view of the assembly of  FIG. 1  in a second position; 
           [0029]      FIG. 4  is a top view of the door guard plate of  FIG. 1 ; 
           [0030]      FIG. 5  is another top view of the assembly  FIG. 1 ; 
           [0031]      FIG. 6  is a perspective view of part of the assembly of  FIG. 1 ; 
           [0032]      FIG. 7  shows parts of the assembly of  FIG. 1 ; 
           [0033]      FIG. 8  is a top view of a second assembly in accordance with the present invention; 
           [0034]      FIG. 9  shows a chain for use with the assemblies of the present invention; 
           [0035]      FIG. 10  is a front view of the part of the chain of  FIG. 9 ; 
           [0036]      FIG. 11  is a perspective view of part of a third assembly in accordance with the present invention; 
           [0037]      FIG. 12  is a top view of the third assembly in a first position; 
           [0038]      FIG. 13  is a top view of the assembly of  FIG. 12  in a second position; 
           [0039]      FIG. 14  shows a fourth assembly in accordance with the present invention; 
           [0040]      FIG. 15  illustrates a further view of the assembly of  FIG. 14 ; 
           [0041]      FIG. 16  is a top view of a fifth assembly in accordance with the present invention; 
           [0042]      FIG. 17  is a top view of a sixth assembly in accordance with the present invention; 
           [0043]      FIG. 18  is a top view of a seventh assembly in accordance with the present invention; 
           [0044]      FIG. 19  shows an eighth assembly in accordance with the present invention; 
           [0045]      FIG. 20  shows a ninth assembly in accordance with the present invention; 
           [0046]      FIG. 21  shows a tenth assembly in accordance with the present invention; 
           [0047]      FIG. 22  shows an eleventh assembly in accordance with the present invention; 
           [0048]      FIG. 23  shows a first part for use in a twelfth assembly in accordance with the present invention; 
           [0049]      FIG. 24  shows a second part for use with the part of  FIG. 23 ; 
           [0050]      FIG. 25  shows an alternative second part for use with the part of  FIG. 23 ; 
           [0051]      FIG. 26  is a perspective view of a thirteenth assembly in accordance with the present invention; 
           [0052]      FIG. 27  is a perspective view of a further part for use in the assembly of  FIG. 26 ; 
           [0053]      FIG. 28  is a perspective view of parts shown in  FIGS. 27 and 28  in an assembled arrangement; 
           [0054]      FIG. 29  is a further view of the assembly of  FIG. 26 ; 
           [0055]      FIG. 30  is a perspective view of a fourteenth assembly in accordance with the present invention; 
           [0056]      FIG. 31  is a perspective view of a fifteenth assembly in accordance with the present invention in a first position; 
           [0057]      FIG. 32  is a perspective view of the assembly of  FIG. 31  in a second position; 
           [0058]      FIG. 33  is a perspective view of a sixteenth assembly in accordance with the present invention; 
           [0059]      FIG. 34  is a perspective view of a seventeenth assembly in accordance with the present invention; 
           [0060]      FIG. 35  is a top view of a eighteenth assembly in accordance with the present invention; and 
           [0061]      FIG. 36  is a perspective view of part of the assembly shown in  FIG. 35 . 
       
    
    
     DETAILED DESCRIPTION 
       [0062]      FIGS. 1 to 7  show a first example of a door chain according to the present invention, in which a door chain assembly  1  is provided. The illustration of  FIG. 1  shows the assembly fixedly secured to a door and door frame, with the door chain is in its operative or standby condition, wherein one end of the guard chain  30  is secured to the door frame anchor plate  50  by means of its end link  31   a . The end link  31   a  engages the metal loop  52  which forms part of the anchor plate  50 , with the anchor plate  50  fixedly secured to the door frame with screws  15 . The free end of the guard chain  30  is releasably secured in the narrow slot portion  27  in the door guard plate  20 , the guard chain  30  having gained entry to the narrow slot  27  by means of the slot aperture  26 , which has a diameter that allows passage of the guard chain  30 . The slot aperture  26  is closed, blocked or covered by a handle  40  which is spring biased to the closed position, as shown in  FIGS. 2 and 3 . It is necessary to move the handle  40  transversely on the guard plate  20  against the force of a small compression spring  36  to provide chain access to the slot aperture  26 . The free end of the guard chain  30  may then be lowered through the slot aperture  26  and a chain link  31  selected for engagement in the narrow slot  27 , the selected link  31  is then moved to abut the slot end  27   a  of the narrow slot  27 . The slot  27  is a closed slot that has solid periphery. 
         [0063]    In the illustration of  FIG. 1 , the third link  31  from the free end of the guard chain  30  is engaged in the narrow slot  27 , engaging the second link on the free end of the chain in the slot  27  will allow the door to be opened the maximum amount allowed by the guard chain. In this manner link selection determines the amount a door may be opened for inspection of a caller, allowing for varying degrees of limited opening of a door. After inspection of a caller the door must be closed to permit removal of the chain  30  from the door guard plate  20  to allow the door to be opened fully. 
         [0064]    The door guard plate  20  is in the form of a “T” bar, which comprises a chain-receiving plate in the form of a central rib  23  and a back plate in the form of extended flanges  22 . Back plate of the ‘T’ bar provides a pair of extended flanges  22  and  22   a  that are provided respectively with several spaced screw fixing apertures  14  by means of which the guard plate  20  is fixedly secured to a door. The central rib  23  of the ‘T’ bar extends beyond the end of the extended flanges in the direction distal from the door frame. The extension portion  29  of the central rib  23  is also reduced in width and acts to support a handle  40 . 
         [0065]    The central rib  23  comprises a slot aperture  26  centrally therein, from which a pair of opposing narrow slots  27  and  28  respectively extend outwardly from the slot aperture  26 . The slots  27  and  28  extend centrally and transversely in the central rib to their respective slot ends  27   a  and  28   a,  which are adjacent each end of the central rib  23 . The long narrow slot  27  which extends towards the front of the guard plate  20 , in use, is engaged by the guard chain  30 , the short narrow slot  28  accommodates a small compression spring  36  which acts to bias the guard plate handle  40 . 
         [0066]    The slot aperture  26  facilitates entry of the free end of the guard chain  30  into the door guard plate  20 . A link  31  of the guard chain  30  is selected for engagement in the narrow slot  27  and the chain  30  is inserted into the aperture. The selected link  30  is then positioned in, and moved along, the slot  27  towards the front of the door guard plate until the link  31  abuts the slot end  27   a.  The slot  27  is slightly wider than the diameter of wire from which the chain links are formed, to ensure that a chain link can only pass sideways through the narrow slot  27 . Thus, the adjacent link of the chain acts as a stop, thereby providing an interlock between the guard chain  30  and the door guard plate  20 . A number of different links on the free end of the guard chain  30  may be engaged within the slot  27  to releasably secure the guard chain  30  to the door guard plate  20 . Individual links of the chain  30  directly engaging the door guard plate  20  provide varying degrees of selective and secure limited opening of the door for inspection purposes and the length of the chain  30  restricts the amount by which the door may be opened. The slot aperture  26  and narrow slot  27  being located on the horizontal plane, facilitates easy engagement of the free end of the guard chain  30  and thereby a selected link  31 , in the door guard plate  20 . 
         [0067]    The rear narrow slot  28  in the extended portion  29  of the central rib  23  of the door guard plate  20  is arranged to house a short compression spring  36  the spring  36  comprises a closed loop  37  at one end to receive a retaining pin  39 . The spring  36  acts to bias the door guard plate handle  40  to its closed position, in which position it blocks access to the slot aperture  26 . 
         [0068]    A handle  40  is provided, which may be fabricated from metal or plastic, the external profile of that handle  40  is generally rectangular and is provided with a transverse recess  42  which allows that handle  40  to be mounted on the narrow portion  29  of the central rib  23  and to be a snug, slidable fit thereon. A portion of the sides  43  and  43   a  of the handle  40  are been removed, indicated by numeral  45  to allow the front end of the handle  40  to project onto the central rib  23  to cover the slot aperture  26  when the handle  40  is in its closed position, as shown in  FIGS. 2 and 3 . Stop faces  46  on the handle  40  engage the pair of stop faces  25  on the back end of the central rib  23  to limit inward travel of the handle  40 . A pair of pin receiving apertures  44  and  44   a  are defined centrally and adjacent the front of the handle  40  and gripping corrugations  47  or the like may be provided on the top and bottom surfaces of the handle  40 . 
         [0069]    In order to assemble the handle  40  on the door guard plate  20  the spring  36  is first loaded into the short rear slot  28  of the central rib  29 , as shown in  FIG. 5 , and the handle  40  is then slidably mounted on the narrow portion  29  of the central rib  23  captivating the compression spring  36  on the door guard plate  20 . The spring  36  is then compressed against the slot end  28   a  to align the loop  37  on the end of the spring  36  with the pair of apertures  44  and  44   a  in the handle  40 . The retaining pin  39  is inserted to locate in and bridge the apertures  44  and  44   a  and be engaged in the loop  37  of the spring  36 . The handle  40  is secured on the door guard plate  20  and spring biased transversely thereon to its closed position, in which position it blocks access to the slot aperture  26 . 
         [0070]    In order to engage the guard chain  30  in the door guard plate  20  the handle  40  is first moved transversely on the central rib  23  against the force of the spring  36  sufficient to expose the slot aperture  26 . At this point the spring  36  may have “bottomed”, whilst holding the handle  40  in its open position with one hand the free end of the guard chain  30  is lowered through the slot aperture  26 . A link  31  is selected for engagement in the narrow slot  27  and the selected link  31  is moved to abut the slot end  27   a,  as shown in  FIG. 4 , after which the handle  40  is then released to automatically close the slot aperture  26 . Thus, the guard chain  30  is releasably secured in the door guard plate  20  and cannot be accidentally or inadvertently disengaged from the door guard plate  20 . In one construction, when the handle  40  is moved to its open position against the force of the spring  36 , it will remain in the open position unaided while the guard chain  30  is being engaged in the door guard plate  20 . The handle  40  may then be manually released to close the slot aperture  26 . 
         [0071]    To disengage the guard chain  30  from the door guard plate  20  the handle  40  is moved transversely on the guard plate  20  against the force of the spring  36  to its open position, exposing the slot aperture  26 . With the handle  40  in its open position, the guard chain  30  is moved transversely in the narrow slot  27  and into the slot aperture  26  and the free end of the guard chain  30  can be lifted out of the door guard plate  20 . 
         [0072]      FIGS. 8 to 10  show a door frame anchor plate  50  described in the previous embodiment and illustrated in  FIG. 1  in conjunction with a door guard plate  20   a . The door guard plate  20   a  comprises a short length of metal, generally in the form of a ‘T’ section. The main body  21  of the door guard plate  20   a  provides a pair of extending flanges  22  and  22   a.  The flanges  22  and  22   a  are provided, respectively, with several spaced screw fixing apertures  14  by means of which the door guard plate  20   a  is fixedly secured to a door. The main central rib  23  of the door guard plate  20   a  extends past the flanges  22  and  22   a  on the end of the door guard plate that, in use, is furthest away from the door jamb. 
         [0073]    The central rib  23  defines a keyhole slot which comprises a slot aperture  26 , dimensioned to permit passage of the guard chain  30 , which is provided centrally and adjacent the back end of the central rib  23 . A narrow slot  27  extends outwardly from the slot aperture  26  centrally and transversely in the central rib  23  to a slot end  27   a  adjacent the front end of the door guard plate  20   a.  In use, the free end of the guard chain  30  is releasably secured in the narrow slot  27 . 
         [0074]    A chain handle  60  is provided and is secured in the last link  31   b  on the free end of the guard chain  30 . The handle  60 , which is in the form of a generally oval metal or plastic disc is stepped  63  to provide a primary body portion  61  and a secondary body portion  62 . The primary body portion  61  is dimensioned such that it cannot pass through the narrow slot  27  and can only pass sideways through the slot aperture  26 . The width of the secondary body portion  62  of the handle  60  is dimensioned to allow it to pass through the narrow slot  27  thus the handle  60  can only pass sideways through the slot aperture  26  and narrow slot  27  and therefore requires manipulation. An elongated slot  64  is defined centrally in the secondary body portion  62  the aperture  64  extends from the step  63  to adjacent the top of the handle  60 . The last link  31   b  on the free end of the guard chain  30  is fixedly secured in the slot  64  in the guard chain handle  60 , the other end of the guard chain  30  is secured to the door frame anchor plate  50  by means of its end link  31   a.    
         [0075]    The chain handle  60  facilitates engagement and disengagement of the free end of the guard chain  30  in the door guard plate  20   a.  Requiring that the handle  60  be manipulated in order for the guard chain  30  to be removed from the door guard plate  20   a  ensures that the guard chain  30  cannot accidentally or inadvertently disengage the door guard plate  20 . 
         [0076]    In order to engage the guard chain  30  in the door guard plate  20   a,  the handle  60  is held on its side and partially entered into the narrow slot  27  and slot aperture  26 , releasing the handle  60  will cause it to swivel through the narrow slot  27  and aperture  26  on the link  31   b  which is straddling the narrow slot  27 . The link  31   b  is then moved transversely using the free end of the guard chain  30  to be positioned over the slot aperture  26 , at which time the free end of the guard chain  30  may be lowered through the slot aperture  26 . A link  31  is then selected and engages in the narrow slot  27  and is moved transversely therein to abut the slot end  27   a.  The guard chain  30  is now releasably secured in the door guard plate  20   a.    
         [0077]    To disengage the guard chain  30  from the door guard plate  20   a,  the free end of the guard chain  30  is moved transversely to disengage the narrow slot  27  and locate in the slot aperture  26 . The guard chain  30  may then be drawn upwards through the slot aperture  26  until the handle  60  abuts the side of the aperture  26 . When the guard chain  30  is moved transversely so that the link  31   b  straddles the narrow slot  27 , the handle  60  on the link  31   b  is swiveled and the handle  60  is pushed upwards and through the narrow slot  27  and slot aperture  26 . 
         [0078]      FIGS. 11 to 15  show door guard plates which employ a plastic or metal closure to shield the slot aperture  26 . The closures are required to be moved manually between open and closed positions and are provided to prevent the guard chain  30  inadvertently disengaging the door guard plate. 
         [0079]      FIGS. 11 to 13  show a door guard plate  20   b,  which has a closure  70  that is swivelably mounted on the extension  29   a  of the central rib  23  by means of the swivel pin  39   a.  The swivel pin  39   a  extends through a pair of apertures  75  on the closure  70  and the pin aperture  26   a  (not shown) in the central rib extension  29   a.  The closure  70  defines a large open, through slot  74  in one side that is dimensioned to receive the central rib  23 . In this manner the closure  70  can cover the slot aperture  26  on both sides of the central rib  23 .  FIG. 11  is a perspective view of the closure  70 . 
         [0080]      FIG. 12  shows the closure  70  secured to the central rib  23  on the door guard plate  20   b,  by means of the swivel pin  39   a.  The closure  70 , in its closed position, blocks access to the slot aperture  26  preventing removal of the guard chain  30  from the door guard plate  20   b.    FIG. 13  shows the closure  70  in its open position, after being swivelled on the pin  39   a,  allowing access to the slot aperture  26  for removal or insertion of the free end of the guard chain  30 . A handle  60  is not required on the free end of a guard chain  30  if the door guard plate has a slot aperture  26  closure. Any available link  31  will act as an interlock between the guard chain  30  and the door guard plate  20   b.    
         [0081]      FIG. 14  illustrates a door guard plate  20   c  that supports a plastic or metal closure  80 , which is in the form of a disc having a peg  82  depending outward from its underside. The peg  82  is close to the periphery of the body  81 . A small annular bead  83  is provided on the end of the peg  82  which is a push fit into the aperture  26   a  (not shown) in the central rib extension  29   a.  In  FIG. 14 , the closure  80  is shown in its closed position in which position it blocks access to the slot aperture  26 , the closure is  80  is swivalable between its two positions on the peg  82 . As doors may be hinged on their left or right sides, the closure  80  can be forced out of the central rib extension  29   a  and inserted on either side thereof to change the orientation of the assembly. 
         [0082]      FIG. 15  shows a door guard plate  20   d  supporting a plastic closure  90  which has an annular stepped body  91  which is attached to a peg  94  by a hinge portion  93 , the peg  94  defines a small annular bead adjacent its free end and is a force fit into the aperture  26   a  (not shown) in the central rib extension  29   a.  The reduced diameter portion  92  of the main body  91  of the closure  90  is a snug fit in the slot aperture  26  when the closure  90  is in its closed position  FIG. 15  shows the closure  90  in its open position, in which the free end of the guard chain  30  is able to access and engage the door guard plate  20   d.  As with the previous example, the closure  90  can be engaged on either side of the central rib extension  29   a.    
         [0083]      FIG. 16  shows a door guard plate  20   e  comprising a slot aperture  26  that will not allow direct passage of the free end of the guard chain  30 . In order to releasably secure the guard chain  30  in the door guard plate  20   e  each of the links  31  on the free end of the guard chain  30  are required to be singularly, manually manipulated. Each link  31  is required to be aligned sideways with the narrow slot  27  when it can be lowered through the slot aperture  26  and narrow slot  27  until the following link  31  abuts the side of the slot aperture  26 . The guard chain  30  is then rotated 90 degrees to align the adjacent link  31  with the narrow slot  27 , at which time it can be lowered until it abuts the side of the slot aperture  26 . In this manner the free end of the guard chain  30  is entered into the door guard plate  20   e.    
         [0084]    When, for example, a person selects and loads the fourth link  31  from the free end of the guard chain  30  into the door guard plate  20   e,  that fourth link is then moved transversely in the narrow slot  27  to abut the slot end  27   a  and the guard chain  30  is then releasably secured in the guard plate  20   e.  The guard chain  30  is quickly loaded into the door guard plate  20   e  by alternating rotation i.e. 90 degrees clockwise then 90 degrees anticlockwise; rotating the guard chain  30  clockwise then anticlockwise, alternately, prevents twisting of the guard chain  30 . 
         [0085]    To disengage the guard chain  30  from the door guard plate  20   e,  the free end of the guard chain  30  is moved transversely in the narrow slot  27  and into the slot aperture  26  to the position illustrated in  FIG. 16 . The guard chain  30  is then rotated alternately 90 degrees clockwise then 90 degrees anticlockwise until the guard chain  30  disengages the door guard plate  20   e.  Requiring that the guard chain  30  be manipulated in this manner ensures that it cannot inadvertently or accidentally disengage the door guard plate  20   e.    
         [0086]      FIGS. 17 and 18  show two door guard plates,  20   f  and  20   g,  which are almost identical to the door guard plate  20   a  of  FIG. 8 . The difference between the device of  FIG. 8  and the one shown herein is that the narrow slot  27  in the door guard plates  20   f  and  20   g  has been modified or configured in order to reduce the risk of accidental or inadvertent disengagement of the guard chain  30  from the door guard plates  20   f  and  20   g  when the door chain  1  is operational. 
         [0087]      FIG. 17  illustrates a door guard plate  20   f  in which the narrow slot  27   b  defines corrugations  27   c  along its length. The corrugations  27   c  provide a tortuous path for the selected link  31  to traverse. When the door chain  1  is operational and the link  31  abuts the slot end  27   a,  should the door be violently kicked by a would-be intruder, the corrugations  27   c  provide resistance to transverse movement of the guard chain  30  in the narrow slot  27   b.  The door guard plate  20   g  of  FIG. 18  comprises a link enclosure  24  at its slot end which is configured to retain the selected link  31  at the slot end  27   a  of the door guard plate  20   f,  in order to prevent the guard chain  30  inadvertently disengaging the narrow slot  27   d.    
         [0088]      FIGS. 19 to 22 , illustrate door guard plates that utilise resilient means to prevent inadvertent disengagement of the guard chain  30  from the door guard plates. 
         [0089]      FIG. 19  shows a door guard plate  20   h  that employs a torsion spring  100  to interfere with the passage of a selected link  31  in the narrow slot  27 . The torsion spring  100  is secured to the door guard plate  20   h  by a fixing screw  15  which locates within the coils  101 . The head of the screw  15  grips a reduced diameter coil  103  at the fixed end of the spring  100 . The other free end of the spring  100  comprises a leg  102 , which is bent at 90 degrees to the spring body  101  and that is spring biased against the central rib  23  of the door guard plate  20   h.  The leg  102  extends partially into over the narrow slot  27  so as to interfere with the passage of a selected link  31  engaged therein. A selected link  31  is required to be forced past the spring leg  102  as it is being moved to abut the slot end  27   a.  To releasably secure the guard chain  30  in the door guard plate  20   h  the free end of the guard chain  30  is lowered through the slot aperture  26  and it engages the selected link  31  in the narrow slot  27 . The chain  30  is then pulled sideways on the guard chain  30 . The link  31  will abut the spring leg  102 , then move the selected link  31  past the spring  100 , against the resistance of the spring leg  102  to abut the slot end  27   a.    
         [0090]      FIG. 20  illustrates a door guard plate  20   i,  which also utilises a torsion spring  100   b.  In this embodiment, a loop  104  on the free end of the spring  100   a  projects partially over the narrow slot  27  to obstruct passage of a selected link  31  therein. The spring loop  104  is spring biased against the surface of the central rib  23 . The extended leg potion  105  of the loop  104  is spring biased against the flange  22 . The method of engaging the guard chain  30  in the door guard plate  20   i  is the same as the example of  FIG. 19 . 
         [0091]      FIG. 21  shows a door guard plate,  20   j,  which incorporates a torsion spring, wherein the leg  106  on the free end of the spring  100   b  interferes with the passage of the free end of the guard chain  30  in the slot aperture  26  to provide resistance to inadvertent removal of the guard chain  30  from the door guard plate  20   j.  To releasably secure the free end of the guard chain  30  in the door guard plate  20   j,  the first link  31  is entered into the slot aperture  26  and pulled down on until the ‘selected’ link  31  is aligned with the narrow slot  27 . The guard chain  30  is then moved sideways until the ‘selected’ link  31  abuts the slot end  27   a.  To disengage the guard chain  30  from the door guard plate  20   j  the engaged link  31  is moved transversely into the slot aperture  26  and the free end of the guard chain  30  is pulled out of the door guard plate  20   j,  the spring leg  106  will flex as alternate links  31  are withdrawn. 
         [0092]      FIG. 22  illustrates a door guard plate  20   k  that employs a spring clip  100   c  to provide resistance to passage of a selected link  31  in the narrow slot  27 . The spring wire clip  100   c  has a main body  108  which is curved. The end  107  of the spring clip  100   c  is bent at 180 degrees to form a hook  110 , which passes through an elongated slot  121  in the central rib  23  to anchor the end  107  of the spring clip  100   c  to the central rib  23 , the other end  109  of the spring clip  100   c  is bent to form a hook  111  which also passes through an elongated slot  120  in the central rib  23  to anchor the other end  109  of the spring clip  100   c  to the central rib  23 . The main body  108  of the spring clip  100   c  is spring biased against the surface of the central rib  23  and projects partially over the narrow slot  27  to provide resistance to passage of a selected link  31  therein. All other aspects of this example, including engaging and disengaging the guard chain  30  in the door guard plate  20   k,  have been covered in relation to  FIGS. 19 and 20 . 
         [0093]      FIGS. 23 to 25  illustrate an example of a back plate and two chain-receiving plates according to the present invention. The plates are fabricated as a pressing from a flat metal strip or blank, although they may be produced by way of laser cutting a large sheet of metal. 
         [0094]      FIG. 23  is a perspective view of the back plate, which comprises a number of spaced screw receiving apertures adjacent the sides thereof, along with three spaced elongated slots positioned centrally and transversely therein. The slots are dimensioned to receive three corresponding lugs that extend from the back side of the chain-receiving plates shown in  FIGS. 24 and 25 . The back plate of  FIG. 23  may be used with either of the chain-receiving plates shown in  FIGS. 24 and 25 . 
         [0095]    On assembly of the embodiment shown in  FIGS. 23 to 25 , a chain-receiving plate ( FIG. 24 or 25 ) is engaged on the back plate of  FIG. 23  by engaging the lugs of the chain-receiving plate into the respective apertures of the back plate. Once engaged, the two components are fixedly secured together by welding, which is applied from the back side (the side away from the chain-receiving plate) of the back plate. The welded surfaces may then be easily and quickly dressed on a grinding machine. Thus, when the door guard plate is secured to a door there are no visible signs of welding. 
         [0096]      FIGS. 26 to 29  illustrate a further example of a door guard plate  20   p  which may be formed as a pressing by piercing and folding a flat metal blank or strip. The door guard plate  20   p  performs the same function as the guard plate  20   a  of  FIG. 8 . The door guard plate  20   p  is generally a short ‘T’ profile bracket having two pairs of lugs  22  and  22   a  respectively extending at 90 degrees outward of the central rib  23  and on either side thereof. Each of the lugs is provided with a screw receiving aperture  14 , by means of which the door guard plate  20   p  is secured to a door. The lugs  22  and  22   a  perform the same function as the extended flanges  22  and  23  of the previously discussed embodiments. A back plate  120 , which may be plastic or a metal die casting, is provided with the door guard plate  20   p.  The back plate  120  acts as a door edge protector and to improve aesthetics. Recesses  122  and  122   a  are provided in the front face  122  of the back plate  120  to receive the lugs  22  and  22   a  respectively of the door guard plate  20   p  in order that the lugs  22  and  22   a  may be flush with the front surface  122  of the back plate  120 . Screw receiving apertures  14  in the back plate  120  are aligned with corresponding screw receiving apertures  14  in the lugs  22  and  22   a  in the door guard plate  20   p.  The operational aspects of this example of door guard plate are the same as those for the assemblies shown in  FIGS. 8 and 16 . 
         [0097]      FIG. 30  illustrates a door guard plate  20   q  that is formed as a metal pressing or fabricated from a short length of 90 degree metal angle section. The door guard plate  20   q  is provided with a metal or plastic back plate  130  which acts as a door edge protector. The door guard plate  20   q  comprises a main body  23   a,  which has a slightly shorter flange portion  22  extending therefrom at 90 degrees. The flange  22  is provided with several spaced screw receiving apertures  14 , by means of which it is secured to a door. The longer main body  23   a  of the door guard plate  20   q  defines a slot aperture  26  adjacent its back end and a narrow slot  27  extends outwards from the slot aperture  26 , centrally on the main body  23   a  to a slot end  27   a  which is close to the front end of the main body  23   a.  The back plate  130  is the same length as the flange  22  and just over twice the width. Two sets of screw receiving apertures  14  are provided in the back plate  130  and align with corresponding screw receiving apertures  14  in the flange  22 . The operational aspects of the door guard plate  20   q  are the same as those described in relation to the assemblies of  FIG. 8  and  FIG. 16 . 
         [0098]      FIGS. 31 to 36  show a door guard plate  20   r  that is generally in the form of a short length of metal ‘T’ section. Extended flanges  22  and  22   a,  which extend substantially perpendicularly from each side of the main central rib  23 , are provided with spaced screw receiving apertures  14  for fixedly securing the door guard plate  20   r  to a door. The main central rib  23  extends beyond the flanges  22  and  22   a  on the end of the door guard plate that, in use, is furthest away from the door jamb. The central rib  23  defines a narrow entry slot  27   x  located centrally and transversely therein, leading from the back end of the door guard plate  20   r  to a slot end  27   a  close to the front of the door guard plate  20   r.  The slot  27  facilitates entry and engagement of a link  31  or links on the free end of the guard chain  30  in the door guard plate  20   r  to releasably secure the guard chain  30  to the door guard plate  20   r.    
         [0099]    The entry  27   x  to the narrow slot  27  is at the end of the door guard plate  20   r  that, in use, is furthest away from the door jamb. The slot  27  is on the horizontal plane and facilitates easy engagement of a selected link  31  therein. The links  31  can only pass sideways in the narrow slot  27 , thus the link adjacent a selected link  31  provides an interlock between the guard chain  30  and the door guard plate  20   r . A number of different links on the free end of the guard chain  30  may be engaged singularly in the narrow slot  27  to releasably secure the guard chain  30  to the door guard plate  20   r.  Individual links  31  on the free end of the guard chain  30  directly engaging the door guard plate  20   r,  provide varying degrees of selective and secure limited opening of a door for inspection of a caller. The last link  31   b  on the free end of the guard chain  30  determines the maximum amount the door may be opened. The last link  31   b  may be engaged on the flexible limb  23   a  of the door guard plate  20   r,  the inner surface of the link  31   b  abutting the slot end  27   a.    
         [0100]    An aperture  14   a  is provided at the back end of the central rib  23  adjacent the entry  27   x  on the flange side  23   b  of the narrow slot  27 , the aperture  14   a  is to receive a metal ring R 1 , the ring R 1  is captive in the aperture  14   a  and swivelably moveable therein between an unlocked position, in which it permits access for the free end of the guard chain  30  to the narrow slot  27 , and a locking position, in which, it locks the free end of the guard chain  30  in the door guard plate  20   r,  when the door guard plate  20   r  is operational. An annular cut-out or holding recess  36  is provided in the edge of the resilient limb  23   a  adjacent the free end of the resilient limb  23   a.  The cut-out is provided to locate the one side of ring R 1  when the ring R 1  is in its locking position. 
         [0101]    An angled lead or ramp  37  extends from the holding recess  36  to the end of the limb  23   a  the lead  37  acts to guide the ring R 1  into the holding recess  36  as the ring R 1  is moved up the lead  37  against the force of the resilient limb  23   a  to snap engage the holding recess  36 . The ring R 1  in its locking position, acts to support the flexible limb  23   a  preventing it moving outward of the door guard plate  20   r.  The ring R 1  prevents inadvertent removal of the guard chain  30  from the door guard plate  20   r.    
         [0102]      FIG. 32  is a perspective view of the door guard plate  20   r  which has a ring R 2  releasably secured in the narrow slot  27 . The last link  31   b  on the free end of the guard chain  30  is fixedly secured to the ring R 2  and the ring R 2  is engaged on or over the flexible limb  23   a  of the door guard plate  20   r  and the inside surface of the ring R 2  is abutting the slot end aperture  27   a.  The ring R 2  may be provided on the free end of the guard chain  30  as a handle for the chain. The rings R 1  and R 2  are, preferably, the same size. The guard chain links  31  and the end link  31   b  which is attached to the ring R 2  are required to be engaged singularly and sideways in the narrow slot  27  to provide varying degrees of selective, limited opening of a door. 
         [0103]    A small hump  38  may be provided adjacent the entry  27   x  to the narrow slot  27 , the hump  38  projecting from the flange side  23   b  of the central rib  23  into the narrow slot  27 , the small hump  38  will provide resilient resistance to removal of a selected link or ring R 2  from the narrow slot  27  in the door guard plate  20   r.  The hump  38  would not be required if a locking ring R 1  or slot closure is provided. The slot entry  27   x  may have curved or tapered entry leads  39  to assist in locating a selected link  31  on the free end of the guard chain  30  in the narrow slot  27 . 
         [0104]      FIG. 33  is a perspective view of the door guard plate  20   r  which has a closure  86  swivalably secured on the limb  32   b  adjacent the narrow slot entry  27   x . The closure  86  is secured to the door guard plate  20   r  by means of a swivel pin  39   a , which engages the apertures  88  defined in the body  87  of the closure  86  and the aperture  14   a  in the limb  23   b.  An indent  89  in the side of the closure  86  snap-engages the holding recess  36  in the resilient limb  23   a  of the door guard plate  20   r  when the closure  86  is swivelled to its closed position, in which position it prevents inadvertent disengagement of the guard chain  30  from the door guard plate  20   r .  FIG. 33  shows the closure in its locking position. The flexible limb  23   a  may be depressed inwards to relieve pressure between the flexible limb  23  and the indent  89 , when moving the closure  86  from its locked to its unlocked position, when the free end of the guard chain  30  may be released from the door guard plate  20   r.    
         [0105]      FIG. 34  illustrates an alternative closure  96  for the door guard plate  20   r . The closure  96  comprises a short, thin walled rectangular sleeve, of which the back end  99  is closed and is preferably slightly curved. The internal bore  98  of the closure  96  is dimensioned to be a snug fit on the central rib limbs  23   a  and  23   b.  The resilient, flexible limb  23   a  will provide that the closure  96  is firmly gripped when it is pushed onto the door guard plate  20   r  to lock the free end of the guard chain  30  therein. In use, the closure  96  is stowed on the door guard plate  20   r  and is only removed to allow the guard chain  30  to be releasably secured in the guard plate  20   r.    
         [0106]      FIGS. 35 and 36  illustrate the door guard plate  20   r  which has been modified to enable it to receive a thumb clip  130  as means to prevent the free end of the guard chain  30  inadvertently disengaging the door guard plate  20   r.  The door guard plate  20   r  is provided with a pair of spaced apertures  14   b  adjacent the free ends of the limbs  23   a  and  23   b  respectively, the opposing apertures  14   b  are to receive respective prongs  14   c  on the double pronged thumb clip  130 . The thumb clip  130  is used to bridge the narrow slot  27  to prevent inadvertent disengagement of the free end of the guard chain  30  from the door guard plate  20   r  when the door chain  1  is operational. 
         [0107]    The thumb clip  130  comprises a short narrow body  131 , the sides  132  of which are dished to facilitate gripping and the back end  133  of the thumb clip  130  is curved. A pair of spaced prongs  14   c  extend outwardly from the front end  134  of the thumb clip  130 . The prongs  14   c  engage and locate respectively in the apertures  14   b  in the door guard plate  20   r.  The length of the prongs  14   c  ensures that the thumb clip  130  is adequately engaged in the door guard plate  20   r.  In use, the thumb clip  130  is stowed on the door guard plate  20   r  and is only removed to allow the guard chain  30  to be releasably secured in the guard plate  20   r.    
         [0108]    It is to be understood, that any suitable door frame anchor plate  50  or anchor means may be used in conjunction with the door guard plates illustrated and described in this specification, to fixedly secure one end of the guard chain  30  to a door frame. 
         [0109]    The same numerals have been used throughout this specification to denote similar components.