Abstract:
A door security brake that applies a combination of frictional and gravitational force sufficient to secure a door against intrusive force, yet is easily transported in and out of its door securing position. Frictional force is provided by interchangeable frictional pads that face the floor adjacent to a door. Gravitational force is provided by a reservoir which can be filled with a variety of weight materials. Methods for transporting, employing, and storing a door security brake.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to a novel door security device. More particularly, the present invention relates to a portable security door stop which exerts a combination of frictional and gravitational force to prevent the movement of a door. The present invention also relates to a method for using a portable security door stop to prevent the entry of and intruder and to prevent the closing of an open door. 
       BACKGROUND OF THE INVENTION 
       [0002]    Prior art door security blocking devices have generally used the principle of leverage to resist the movement of a door. Force exerted against one side of the door is levered by these devices against the floor on the opposite side to create resistance to the movement of the door. Levering door blocking devices have included wedge-shaped objects designed to fit into a space between door and floor. Examples include U.S. Pat. No. 5,011,203 to Tackett, and U.S. Pat. No. 5,711,560, to Gilbertson. Wedge-like door security devices have several disadvantages. They cannot be used where there is little clearance below the door, for example when weather stripping is present. If the gap between door and floor is sufficiently large, the door can partially open before the wedge is engaged. The opening door gathers momentum before it strikes the wedge, increasing an intruder&#39;s ability to displace the wedge, and at the least allowing the intruder to reach inside the door with hand or tools. Most importantly, there is only a small area of contact between the device and the floor. With little surface area, there is little friction between the wedge and the floor, so little lateral frictional force is directed toward the door. The result is that the resistance of the device can be overcome by a relatively small inward force on the door. 
         [0003]    Prior art devices have also included braces or props to transfer the force of the door to the floor. These devices have the disadvantage of requiring costly materials of high tensile strength and complex designs, as in the device door brace disclosed in U.S. Pat. No. 4,136,899 to Frasher. Door braces and props also often require the installation of components in the door, floor, or both, as disclosed for example in U.S. Pat. No. 4,019,765 to Nichola. This makes them difficult to move from door to door to meet changing needs. It also makes them no stronger than the fasteners that anchor them. 
         [0004]    A most effective principle of door blocking is the application of a combination of gravitational and lateral frictional force to one side of the door. A door cannot be opened if it is opposed by a body of sufficient weight and adhesiveness to the substrate. This principle has not been applied in prior art devices, in part because bodies of sufficient weight are too heavy to be routinely positioned and removed by a person of normal strength and agility, and in part because means of providing sufficient frictional force against a floor have been lacking. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention provides a security door stop that applies a combination of frictional and gravitational force sufficient to secure a door against intrusive force, yet is easily transported to and from its door securing position. The tenacious hold of the security door stop on a substrate is produced by a novel combination of weight acting upon an interchangeable frictional surface that optimally engages the weight with the substrate. The transportability of the security door stop of the present invention is achieved through novel features including wheels or a slidable surface to facilitate movement across a substrate, and a fillable reservoir that enables the user to reduce or remove the weight of the security door stop for transport. Variations on the security door stop of the present invention enable the user to secure both inward opening doors and outward opening doors. 
         [0006]    The present invention also provides a security door stop that can be fabricated at any conceivable scale to secure any conceivable door, and that can be constructed from inexpensive materials of low tensile strength. 
         [0007]    The present invention further provides methods of transporting, deploying, and storing a security door stop that applies a combination of frictional and gravitational force sufficient to secure a door against an opening force. 
         [0008]    The preferred embodiment of the security door stop of the present invention includes container means to contain a weight material; frictional means to engage the weight of that material with a substrate, typically a floor adjacent to a door; and abutment means for contacting the surface of a door. A preferred embodiment also includes transport means for moving the security door stop into and out of position. The preferred rectanguloid form of the security door stop provides a large surface area over which frictional means can engage the floor. In a preferred embodiment, container means is a reservoir capable of being filled and emptied, and the contained weight material is water. By filling or emptying the reservoir, the user can adjust the weight of the security door stop as needed for security, transportation, and storage. 
         [0009]    In a preferred embodiment, frictional means is an interchangeable pad selected by a user according to the nature of a floor. For a smooth floor, the present invention provides a pad of rubber treads that individually grip the floor. The gripping action of the plurality of rubber treads provides a large accumulative resistance force. Also, as the rubber treads are shifted into the engaged position, a great amount of force is absorbed into the frictional pad. Once engaged, the rubber treads stretch and rebound, providing additional resistance force. For a carpeted floor, the present invention provides a pad that bears teeth or nubs, in addition to friction bearing rubber treads, to engage the fibers a carpet. 
         [0010]    The security door stop of the present invention is generally positioned on the side of a door interior to the space to be secured, with abutment means firmly in contact with a door surface. This prevents an intruder from interfering with the security door stop. In a preferred embodiment, abutment means is a sidewall of the security door stop, protected by a shock absorbing frictional pad. The shock absorbing frictional pads create an opposing force of resistance to the bottom pad, preventing momentum from an inward opening door. In situations in which a door opens outward from the space to be secured, the security door stop can be still be positioned on the interior side of the door, but in an embodiment that includes a chain or wire and bracket that attaches to the underside of the door. By means of this chain or wire and bracket, the frictional resistance and gravitational force of the security door stop are deployed to counteract an outward intrusive force. 
         [0011]    In the preferred embodiment, transport means is at least one wheel, more preferably two wheels, to permit rolling movement across a substrate; and a handle opposite the wheels to facilitate rolling movement. As the security door stop of the present invention can be of any conceivable size to match any conceivable door, a variety of transport means is also provided. For larger embodiments, transport means can include motorized wheels. For smaller embodiments, transport means can include a handle and a slidable surface to enable a user to drag the security door stop easily over a substrate. Transport means can also include only a handle. 
         [0012]    The preferred security door stop of the present invention secures a door when it is in prone position i.e. with frictional means in contact with the substrate and one sidewall is in contact with the door. The security door stop is taken out of operation and readied for transport or storage by grasping the handle and pivoting the reservoir about the axle of the wheels into travel position, i.e. a partially upright position with long axis between approximately one degree and 90 degrees above the substrate. The security door stop may be rested or stored in fully upright position, i.e with long axis approximately 90 degrees above the substrate. A support foot is provided so that the security door stop rests stably in upright position. 
         [0013]    In a preferred embodiment, container means includes a balancing wing, a branch of the reservoir that extends higher than the water filling line when the security door stop in prone position. The balancing wing is therefore empty of water when the security door stop is in prone position. When the security door stop is pivoted into travel position, the balancing wing fills at least partially with water. This shifts the center of gravity downward and over the wheels, thereby facilitating rolling movement. 
         [0014]    The security door stop of the present invention may also be utilized as a door stop to limit or prevent the movement of an open door in any direction. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
           [0016]      FIG. 1  is a side view of the security door stop of the present invention in position to counteract intrusive force against a door; 
           [0017]      FIG. 2  is a top oblique perspective view of the security door stop; 
           [0018]      FIG. 3  is a longitudinal cross section of the security door stop taken at the level of the filling port; 
           [0019]      FIG. 4  is a bottom oblique perspective view of a security door stop showing a tread-bearing embodiment of a frictional pad; 
           [0020]      FIG. 5  is a side detail view of multiple embodiments of the frictional pad of a security door stop; 
           [0021]      FIG. 6  is a top view of a security door stop; 
           [0022]      FIG. 7  is a side view of a security door stop; 
           [0023]      FIG. 8  is a bottom view of a security door stop; 
           [0024]      FIG. 9  is a top view of an embodiment of a security door stop that excludes wheels; 
           [0025]      FIG. 10  is a side view of an embodiment of a security door stop that excludes wheels; 
           [0026]      FIG. 11  is a top oblique perspective view of an embodiment of a security door stop that excludes wheels; 
           [0027]      FIG. 12  is a bottom view of an embodiment of a security door stop that excludes wheels. 
           [0028]      FIG. 13  is a longitudinal cross section of an embodiment of a security door stop that excludes wheels; 
           [0029]      FIG. 14  is a side view of a wedge shaped embodiment of a security door stop; 
           [0030]      FIG. 15  is a side view of an embodiment of a security door stop that is a pentagonal solid; 
           [0031]      FIG. 16  is a side view of an embodiment of a security door stop that prevents the outward movement of a pivoting door; 
           [0032]      FIG. 17A  is a side view of a security door stop including a burglar alarm with a motion sensor affixed to an external surface; 
           [0033]      FIG. 17B  is a side view, partially cut away, of a security door stop including a burglar alarm, with a buoyant motion sensor floating on the surface of liquid weight material; 
           [0034]      FIG. 18A  is a side view of a security door stop with motorized retractable wheels, with wheels in engaged position; 
           [0035]      FIG. 18B  is a side view of a security door stop with motorized retractable wheels, with wheels in retracted position; and 
           [0036]      FIG. 19  is a side view of a security door stop adapted for movement along a door-mounted track. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0037]    The following detailed description illustrates the invention by way of example and not by way of limitation. This description will clearly enable one skilled in the art to make and use the invention, and describes several embodiments, adaptations, variations, alternatives and uses of the invention as disclosed, including what we presently believe is the best mode of carrying out the invention. 
         [0038]    Security door stop, as generally shown in  10 , is a generally rectanguloid hollow body, preferably of a molded plastic material. Security door stop  10  includes an elongated top wall  11  located over an elongated bottom wall  12 , both of which are joined to two opposing side walls  13 , and to two opposing end walls, designated handle end wall  14 , and platform end wall  15 , to define a reservoir  16 . The inner surfaces of all walls are defined as those facing reservoir  16 ; outer surfaces of all walls are defined as those opposite the inner surfaces. Bottom wall  12  is essentially planar. Platform end wall  15  is essentially planar except for the provision of at least one outwardly projecting support foot  17 . Preferably there is a single support foot  17  located in the center of the upper side of platform end wall  15  as shown in  FIG. 1 . Handle end wall  14  includes two outwardly projecting portions  18  joined by handle  19 , such that handle  19  generally spans the distance between sidewalls  13 . In the preferred embodiment, wherein security door stop  10  is formed of blow molded or injection molded plastic, handle  19  is unitarily formed with projecting portions  18 . Alternatively, handle  19  can comprise a separate unit attached by any attachment means well known in the art. In all cases it is essential that handle  19  be situated so as not to disrupt the planar nature of bottom wall  12  or to interrupt the contact of bottom wall  12  with substrate. Side walls  13 , handle end wall  14 , and platform end wall  15  can be completely planar or they may curve at their edges to smoothly join top wall  11  and bottom wall  12 , as shown in  FIG. 2 . 
         [0039]    In the preferred embodiment, abutment means includes either of two sidewalls  13 , and a shock absorbing frictional pad  20  affixed to each sidewall  13 . Affixation is preferably by means of cement, glue, or double sided tape. Less preferably affixation may be by any attachment hardware such as screws, rivets, or clips. 
         [0040]    Frictional pad  21  is affixed to bottom wall  12  by means of an intervening adhesive layer  22 . Preferably, adhesive layer  22  and frictional pad  21  cover as much of bottom wall  12  as possible, to maximize the frictional surface area available to engage a floor. Adhesive layer  22  may be shaped so as to conform exactly to the shape of frictional pad  21 . Preferably, adhesive layer  22  is permanently affixed to bottom wall  12 . Attachment of frictional pad  21  to adhesive layer  22  is preferably reversible, and mediated by a hook and loop fabric system such as Velcro®. Reversible attachment facilitates the interchange of various embodiments of frictional pad  21 . In this manner, frictional pads  21  of particular texture and composition can be matched to particular substrates. Reversible attachment also facilitates the cleaning of frictional pad  21 . Alternatively, frictional pad  21  may be attached persistently or permanently to bottom wall  12  by glue, double sided tape, or any other attachment means known in the art. 
         [0041]    One preferred embodiment of frictional pad  21  is shown in  FIG. 4 . It is a rubber or plastic pad whose floor facing surface bears a plurality of treads  23 . A frictional pad  21  composed of pliable rubber or plastic is optimally suited to frictionally engage smooth surfaced floors such as those of lineoleum, wood, or finished concrete. For surfaces likely to be wet, such as the deck of a boat, a frictional pad  21  composed of a wettable composition such as foam rubber is optimal. The adhesion of the water molecules to the wettable surfaces of frictional pad  21 , combined with the cohesion between water molecules in a thin water film, will produce especially strong binding of frictional pad  21  to a wet floor. Further alternative embodiments of frictional pad  21  are optimal for use on carpeted floors. These embodiments bear a plurality of teeth  24 ; plastic nubs  25 ; or a combination of teeth  24  and plastic nubs  25 , as  FIG. 5 . Still further alternative embodiments of frictional pad  21  include those with floor facing surfaces bearing one or more metal or plastic cleats (not shown) suitable for engaging earth or grass surfaces, or rough surfaces such as unfinished concrete. Other embodiments of frictional pad  21  also include those with floor facing surfaces coated with pressure sensitive removable adhesives similar to the adhesive of Post-it Notes® (not shown). 
         [0042]    Top wall  11  includes filling port  26  which opens into reservoir  16 . Preferably, filling port  16  is centered within an indentation  27  of top wall  11  and is surrounded by a neck  28  which extends upward to a level flush with the rest of top wall  11 . Neck  28  preferably accepts a fluid-tight snap-on cap  29 , which allows a user to seal off reservoir  16  in a fluid-tight manner. 
         [0043]    When in use, reservoir  16  is filled via filling port  26  with a weight material  45 . Preferably weight material  45  is water, although any fluid compatible with the structural materials of security door stop  10  may be used. Alternatively, a flowable solid such as sand or metal shot may be used. In either case, the weight conferring material is admitted to reservoir  16  via filling port  26  and is sealed in place with cap  29 . In an alternative embodiment, reservoir  16  can be permanently filled with a liquid, a flowable solid, or a non-flowable solid such as cement, concrete, wood, or a metal. 
         [0044]    The preferred embodiment of security door stop  10  includes balancing wing  30 , which is essentially an upward protrusion of reservoir  16 . Balancing wing  30  is formed by an upward extension of top wall  11  spanning the distance between upward extensions of sidewalls  13  and platform end wall  15 . In the preferred embodiment, the upward extensions of sidewalls  13  and platform end wall of a height that creates a balancing wing  30  that is approximately 1.5× higher than handle end wall  14 . Balancing wing  30  is asymmetrically disposed toward platform end wall  15 , relative to a center line bisecting security door stop  10  between handle end wall  14  and platform end wall  15 . In the preferred embodiment, the length of balancing wing  30  occupies approximately 40% of the length of sidewalls  13  and 100% of the length of platform end wall  15 . 
         [0045]    Preferably security door stop  10  is fabricated as a single unit from injection molded or blow molded plastic, but it can alternatively be constructed of individually formed parts. Reservoir  16  is preferably integral to the structure but can alternatively be provided as a separate container or liner. In one such alternative embodiment (not shown), security door stop  10  is constructed from metal parts joined by bolting, welding, or other suitable means, which enclose reservoir  16  as a separate plastic container. In still another alternative embodiment, security door stop  10  is constructed of plastic and armored with a puncture resistant cladding of steel, aluminum, Kevlar®, or other puncture resistant material. In this embodiment, security door stop  10  is resistant to attempts by an intruder to puncture reservoir  16  with a sharp object to release weight material. 
         [0046]    An advantage of security door stop  10  is that it can be fabricated at any size suitable to secure doors of any conceivable size and weight. In a preferred embodiment, suitable to secure the front door of a typical home, reservoir  16  contains approximately 924 cubic inches of water and provides a weight of approximately 33 pounds. 
         [0047]    In a preferred embodiment of security door stop  10  the interface between bottom wall  12  and platform end wall  15  is indented to define at least one wheel recess  31  whose closed face extends into reservoir  16  and whose open face opens through bottom wall  12  and platform end wall  15 . Preferably there are two wheel recesses  31 , each located proximate to a corner defined by the intersection of bottom wall  12  and platform end wall  15 . Each wheel recess  31  contains a wheel  32  rotatably fixed to a rigid axle  33 . Axle  33  can be mounted into wheel recess  31  and engaged to wheels by any means of wheel and axle attachment known in the art. Wheel  32  is preferably composed of a durable plastic such as high density polyethylene or nylon, or of metal, or of wood. For large and heavy embodiments of security door stop  10 , wheel  32  may include inflatable tires. Axle  33  is preferably composed of rigid metal or durable plastic such as high density polyethylene or nylon. It is essential that wheel recesses  31  be situated such that wheels  32  are flush with bottom wall  12  as shown in  FIG. 8 . Situated in this manner, wheels  32  do not to disrupt the planar nature of bottom wall  12  and therefore do not interrupt contact of frictional pad  21  with a substrate when security door stop  10  is in prone position. It is also of course essential that wheels  32  project outward from platform wall  15  sufficiently to contact the substrate when security door stop  10  is in travel position. Preferably, wheels  32  project beyond platform wall  15  to a distance identical to the height of support foot  17 , so that security door stop  10  is level when resting in upright position, upon wheels  32  and support foot  17 . 
         [0048]    An alternative embodiment of security door stop  10  is adapted for transport by a sliding or dragging movement across a substrate, or by being carried without contact with substrate. This embodiment, shown in  FIGS. 9-13 , transport means does not include wheels  32 , wheel recesses  31 , or axles  33 . Transport means instead includes slidable surface  34 . A slidable surface is one whose frictional properties are low enough to permit easy dragging movement across a surface and durable enough to sustain repeated movement without significant damage. Preferably slidable surface  34  is faced with a polyfluorocarbon such as Teflon®. Alternatively, the plastic from which security door stop  10  is constructed may possess appropriate frictional and durability properties to provide slidable surface  34  without further modification. Transport means that exclude wheels are well suited to embodiments of security door stop  10  that are small and light in weight, but are not limited to them. 
         [0049]    In an alternative embodiment, security door stop  10  is not rectanguloid but generally wedge shaped, wherein upper wall  11  slopes downwardly to join directly to bottom wall  12  to form a wedge-shaped leading edge  35  that can be inserted under the bottom edge of a door ( FIG. 14 ). In this embodiment, some of the door opening force is transferred by leverage to the substrate, further increasing the effectiveness of the security door stop. Another embodiment that utilizes leverage is a security door stop  10  which is an irregular pentagonal solid wherein one side wall  13  broadly contacts a door, and upper wall  11  slopes downwardly on three steps to join directly to bottom wall  12  to form a wedge-shaped trailing edge  36 , that is, a wedge contralateral to a door ( FIG. 15 ). Other non-rectanguloid shapes are of course possible, limited only by the capabilities of fabrication methods and materials. Such non-rectanguloid embodiments may or may not include wheels  32 , axles  33 , wheel recesses  31 , handle  19 , or support foot  17 , depending on the size and weight of the specific embodiment. 
         [0050]    In an alternative embodiment, security door stop  10  is adapted to secure a door against an outward opening force, that is, a force tending to pull a door away from the location of security door stop  10 . This situation is encountered, for example, when an interior area is secured by a door that swings toward the exterior ( FIG. 16 ). In this embodiment, security door stop  10  is provided with chain  37 , hook  38 , and bracket  39 . Hook  38  is preferably affixed to one side wall  13  of security door stop  10 . Chain  37  joins hook  38  to bracket  39 , which is attachable to the underside of a door. Hook  38  can be of any strong and rigid metal or plastic material, and can be affixed to sidewall  13  by any adhesive or fastening means known in the art; or it can be formed integrally with side wall  13 . Bracket  39  is formed from a metal or plastic of high tensile strength. It is of a size and shape which conforms closely to the underside of a desired door. It can be formed in a manner which allows it to be slipped onto the underside a door and remain in place by means of frictional force, or it may be affixed to the underside of a door with screws, nails, or similar affixation hardware, or by adhesive means. Chain  37  is adapted to be threaded through hook  38  and also attached to bracket  39 . In a preferred embodiment, chain  37  is permanently attached to bracket  39 , for example by welds or rivets, in a manner that leaves two free ends of chain  37  to be threaded through hook  38  and closed by a user by means of a clasp or other means known in the art, thereby forming a closed loop. In this embodiment, the lateral force of the pivoting door is transmitted by chain  37  to engage the treads of frictional pad  21  to grip more tightly to the floor. Alternatively a wire loop (not shown) can be substituted for chain  37 . 
         [0051]    In an alternative embodiment, security door stop  10  includes an alarm triggered by shock or motion. In this embodiment, security door stop  10  not only secures a door but alerts a user to attempts to breach security, and deters further attempts. The alarm can include a motion or vibration sensor of any type well known in the art of burglar alarms, such as a sensor that transmits a signal when a light beam is broken by the motion of an opening door; or a sensor that transmits a signal when a vibration or motion displaces a magnet or causes a trembler device to actuate. In one such embodiment ( FIG. 17A ), motion sensor  40  is mounted a surface of security door stop  10 , preferably an exterior surface. Upon detecting motion, motion sensor  40  transmits a signal to alarm unit  41  via a wireless signal or via wiring  42 . In an alternative embodiment ( FIG. 17B ), buoyant motion sensor  43 , powered by an internal battery, floats on the surface  44  of liquid weight material  45  within reservoir  16 . When security door stop  10  is disturbed, waves induced on the surface  44  of weight material  45  cause buoyant motion sensor  43  to actuate a wireless signal (not shown) to trigger alarm unit  41 . Wireless floating motion sensors are known in the art, e.g. U.S. Pat. No. 4,594,582 to Thompson, and Pool Patrol Pool Alarm, Driven Designs, Inc., Belding, Mich. 48809 
         [0052]    In an alternative embodiment, movement of security door stop  10  is assisted by at least one electric motor engaged directly or indirectly with at least one wheel  32 . In an additional alternative embodiment the motor can be operated by remote control, for example by wire or by radio signal. In this embodiment, not only is movement of the security door stop  10  further facilitated, but security door stop can be activated and inactivated from a distance, including from the outside of the secured door. In a preferred embodiment (FIG.  18 A,B), security door stop  10  includes at two pairs of wheels  32 , each wheel being rotatably engaged to a rigid axle  33 , with each wheel  32  and axle  33  being in turn mounted in a retractable wheel mount  46 . A first pair of wheels  32 , with each wheel in a retractable wheel mount  46 , is attached to one end of security door stop  10 , preferably to opposite sides of platform end wall  15 ; a second pair of wheels  32  is similarly attached to handle end wall  11  (not shown). At least one wheel is driven by a battery powered electric propulsion system, that is, at least one wheel is coupled to a transmission  47  driven by a battery powered electric motor  48 . Preferably all wheels are so driven. The battery powered electric propulsion system can be of any type known in the art, but is preferably the type disclosed in U.S. Pat. No. 5,937,961 to Davidson. The retractable wheel mounts  46  preferably of the type disclosed by U.S. Pat. No. 4,846,493 to Mason, that is, they are pivotably mounted on hinges  49  on any wall of security door stop  10  in a manner that allows them able to pivot from a retracted position, raised above the floor and out of contact with the floor, to an engaged position, in contact with a floor. Thus, when retractable wheel mounts  46  are pivoted into engaged position ( FIG. 18A ), security door stop  10  is raised position, that is, out of operation, with frictional pad  21  not in contact with a floor, and with wheels  31  in contact with a floor. In this raised position, security door stop  10  can travel to and from a door. When retractable wheel mounts  46  are in retracted position ( FIG. 18B ), security door stop  10  is able to secure a door, as frictional pad  21  is in contact with a floor. As in U.S. Pat. No. 4,846,493, the pivoting action of wheel mounts  46  is controlled by at least one horizontally oriented rod  50  which is pivotably attached to a wall of security door stop  10  and which is in turn attached to each retractable wheel mount  46  by means of at least one strut  51 . In this arrangement, movement of horizontally oriented rod  50  in the vertical direction causes any attached retractable wheel mount  46  to pivot into or out of the engaged position. Horizontally oriented rod  50  can be moved by the manual force of a user, or it may be operated by an electric motor, preferably the same battery powered electric motor  48  that drives the wheels. In operation, a user desiring to open a door secured by security door stop  10  first manipulates remote control  52  to cause retractable wheel mounts  46  to pivot into the engaged position, or manually pivots retractable wheel mounts  46  into the engaged position, thus raising security door stop  10  up from, and out of contact with, a floor. User then manipulates remote control  52  to activate battery powered electric motor  48  to drive wheels  32  to move security door stop  10  away from a door. Remote control  52  may actuate signals via wires  42  as in  FIG. 18  or via wireless signals. Equivalent alternative arrangements for retractable wheels are of course possible, for example, wheels can reside in recesses in side walls  13  and ascend and descend by means of a hydraulic drive (not shown). 
         [0053]    In an alternative embodiment, transport means of security door stop  10  includes one or more tracks  53  or rails (not shown) mounted upon a surface of a door. In this embodiment, security door stop  10  can be raised from its door-securing position to a raised position, which permits a door to open. Security door stop  10  is retained in raised position by a catch or chain. Suitable hardware for tracks and retaining means is well known in the art. In this embodiment, security door stop  10  preferably includes top handle  54  attached to top wall  11  to facilitate the raising and lowering process, and may or may not include wheels  32 , axles  33 , wheel recesses  31 , handle  19 , and support foot  17 . 
         [0054]    The following procedure of operation applies to embodiments of security door stop  10  that are not electrically propelled and do not move on tracks or rails. In order to secure a door against opening inward, i.e. into a secured space, user selects a frictional pad  21  appropriate to frictionally engage the specific substrate adjacent to a door and attaches it to adhesive layer  22  of bottom wall  12 . User places security door stop  10  proximate to the door, with frictional pad  21  in contact with the substrate and shock absorbing frictional pad  20  of one sidewall  13  in contact with the door. In the preferred embodiment, full intimate contact of shock absorbing frictional pad  21  with the inner surface of the door is essential for the full securing action of security door stop  10 , for it prevents the door from being partially opened and gathering momentum before striking security door stop  10 . Furthermore, with intimate contact, the lateral force of the opening door is best transmitted to frictional pad  21 , where the forced is absorbed to shift the plurality of treads  23  into the engaged position, thereby creating a large accumulative resistance force. The user then fills reservoir  16  with weight material, preferably water, but, alternatively, reservoir  16  can be filled with weight material prior to placement in front of a door. To secure a door against opening outward, i.e. away from a secured space, security door stop  10  is operated as described above, but user chooses an embodiment of security door stop  10  that includes a chain and, after placing security door stop  10  proximate to the inner side of a door, user attaches the chain of security door stop  10  to a bracket on the inner side of the door. 
         [0055]    To allow the door to open, user grasps handle  19  and lifts it upward from the substrate, so that security door stop  10  pivots on wheels  32 , bringing security door stop  10  to a semi-upright, i.e. traveling, position, wherein all weight is borne on wheels  32 . In the preferred embodiment, featuring balancing wing  30  and a fluid weight material, this motion causes a portion of the weight material in reservoir  16  to flow by gravity into balancing wing  30 . This moves the center of gravity of security door stop  10  downward and centers it over wheels  32 . Essentially, the weight becomes balanced over wheels  32  and this greatly facilitates the rolling movement of security door stop  10 . User then exerts lateral force on handle  19  to cause security door stop  10  to roll away from the door and travel to a desired storage location. At the desired storage location, user applies appropriate lateral force on handle  19  to bring security door stop  10  into fully upright position, that is, a stable position in which all weight is borne on wheels  32  and support foot  17 . For embodiments of security door stop  10  that are electrically propelled or move on tracks or rails, the procedure of operation is essentially as described above, except for the pivoting and positioning steps which are specific to either electric propulsion on retractable wheels or for movement along a track or rails. 
         [0056]    When it is desirable to reduce the weight of security door stop  10 , user removes some or all of the weight material from reservoir  16 . Preferably this is done by removing cap  29  and tipping security door stop  10  so that weight material pours into a receptacle; or by pumping or siphoning out weight material. 
         [0057]    Security door stop  10  can of course be employed as a door stop rather than as a security device. In this use, the operations are as above, but security door stop  10  is deployed at whatever location the user determines to be most advantageous for limiting or stopping the movement of an open door. 
         [0058]    While illustrative embodiments of the invention have been disclosed herein, it is understood that other embodiments and modifications may be apparent to those of ordinary skill in the art and it is intended that this invention be limited only by the scope of the appended claims. 
       REFERENCES  
       [0059]    U.S. Pat. Nos.
   5,011,203   5,711,560   4,136,899   4,019,765   5,937,961   4,846,493