Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.


  1. Advanced Patent Search
Publication numberUS3451708 A
Publication typeGrant
Publication dateJun 24, 1969
Filing dateDec 4, 1968
Priority dateDec 4, 1968
Publication numberUS 3451708 A, US 3451708A, US-A-3451708, US3451708 A, US3451708A
InventorsBrooks Felton D
Original AssigneeBrooks Felton D
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Security apparatus
US 3451708 A
Abstract  available in
Previous page
Next page
Claims  available in
Description  (OCR text may contain errors)

June 24, 1969 F" D. BROOKS 3,451,708

SECURITY APPARATUS Filed Dec. 4, 1968 F E L TON D. BROOKS /N VIE N TOR i ww ATTORNEY United States Patent U.S. Cl. 292--264 3 Claims ABSTRACT OF THE DISCLOSURE In the representative embodiments of the invention disclosed herein, a metal loop adapted to pass over a door knob is coupled to a stout connecting member of limited length for allowing the door to be only partially opened when the loop is fitted over the door knob. By selectively designing the loop to yield without failing under force, an attempted illegal entry of a door or window secured by the present invention will be safely resisted by the controlled deform on of the loop which absorbs such sudden impacts as well as provides an indication of the attempted entry.

This apparatus is a continuation-impart of US. application Ser. No. 661,351, filed Aug. 17, 1967, now abandoned.

Various arrangements of safety chains and the like have, of course, been employed heretofore as a security measure to enable doors and windows to be only partial- 1y opened without risking an unwanted intrusion or a surreptitious disconnection of the security chain. Most, if not all, of the security latches of this nature are, however, generally much stouter than the screws or other fasteners used for attaching them. Thus, although these fasteners may well withstand a relatively steady force, the fasteners typically used will often be jerked out of the door or window frame by sudden impacts. It will also be realized that unless an attempted entry results in physical damage to the woodwork, an attempted entry could well be unnoticed.

Accordingly, it is an object of the present invention to provide new and improved entry-restraining apparatus adapted to withstand sudden impacts as well as to provide a reliable indication of an unsuccessful forcible entry.

This and other objects of the present invention are attained by providing entry-restraining apparatus adapted to releasably latch a door or window to its associated framework and including a loop or ring having a selected limited yield strength. By securing the loop between the door or window and framework, sudden impacts attempting to forcibly open the door or window will only controllably deform the loop to at least partially absorb the impact. Moreover, a surreptitious attempt to force the door or window will deform the loop so as to provide a warning indication that the attempt had been made.

The novel features of the present invention are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may be best understood by way of the following description of exemplary apparatus and methods employing the principles of the invention as illustrated in the accompanying drawings, in which:

FIGURE 1 illustrates one embodiment of the present invention especially adapted for releasably latching a single door; and

FIGURE 2 depicts an alternate embodiment of the present invention especially adapted for releasably latching oppositely-swinging double doors.

Turning now to FIGURE 1, entry-restraining apparatus 10 incorporating the principles of the present invention is shown in position for releasably latching a typical single door 11. -In the preferred form illustrated, the entry-restraining apparatus 10 is comprised of a ring 12 that is detachably interconnected between the door 11 and its associated frame 13 by a short length of a stout cable or chain 14. To secure the chain 14, its free end is coupled to the adjacent door frame 13 by means such as a typical bracket 15 fastened to the frame by bolts or screws 16 of adequate length. The other end of the chain 14 is, of course, connected to the ring 12 in a suitable manner.

It will be appreciated from the drawings that the ring 12 is appropriately sized to facilitate its placement over a projection on the door 11 such as a typical door knob 17. Thus, by suitably proportioning the length of the chain 14 and diameter of the ring 12, the door 11 cannot be opened more than a few inches once the ring is disposed over the door knob 17. This will, of course, permit the door to be safely opened without fear that an intruder might attempt to force the door further open. Similarly, by limiting the free travel of the door 11 in this manner, the chain 114 is so short that the ring 12 cannot be removed [from the knob 17 unless the door is at least nearly closed.

To accomplish the objects of the present invention, the ring 12 is selectively designed to yield or deform without breaking under a tensile load that might be expected to be applied to the ring by one attempting to make a forcible entry through the door '11. In this manner, should an intruder attempt to lunge at the door 11 while it is partially ajar, a substantial portion of the impact against the door will be absorbed as the ring 12 is elongated. Accordingly, instead of imposing a sudden impact against the screws 16 which might possibly rip them from the door frame 13, the controlled deformation or elongation of the ring 12 will dissipate a substantial proportion of the impact. Thus, a frightened occupant would be given sufiicient time to quickly slam the door 11 before another attempt could be made to force an entry.

An added benefit provided by the selective deformational characteristic of the ring 12 is that an undetected surreptitious attempt to force the door 11 simply cannot be made if sufficient force is applied to deform the ring. Thus, even though such an attempt is foiled, the permanent deformation of the ring 12 will be mute testimony that an unlawful entry had been attempted; and even though the occupant is absent, the deformation of the ring 12 will give a clear warning that another attempt might again be made. Thus, in addition to having a police investigation, the occupant can also take appropriate preventative steps.

Turning now to FlGURE 2, an alternate embodiment 20 of the invention as illustrated is shown for releasably latching a pair of oppositely-swinging double doors 21 and 22. As seen there, this alternate security apparatus 20 is comprised of a pair of loops or rings 23 and 24 respectively fitted loosely over the knobs 25 and 26 of the doors 21 and 22 and interconnected by a short length of a stout cable or chain 27. Although only one or the other of the two rings 23 and 24 need to be selectively deformable, it is preferred that both be capable of deformation. Accordingly, it will be appreciated that an attempt to force either or both of the doors 21 and 22 will be effectively resisted in the same manner as previously described and, of course, with similar results.

To determine the physical dimensions as well as the choice of material for the rings 12, 23 or 24, convention'al strength of material formulas are used to assure that the rings will readily deform without breaking under a selected load. In calculating the properties of a selected ring, it will be appreciated that it is primarily the bending moment imposed by the forces on the ring that will cause its deformation. In other words, upon application of force thereto, the bending moment must develop a stress in excess of the allowable yield stress of the selected metal. Once it is determined that a selected ring will deform under a given load, a determination is then made to be certain that the design load will not cause breaking of the ring. if both conditions are met, the selected ring will be suited for use in the present inveniton. 'It should also be noted that, if desired, a ring can be notched slightly to achieve a specific design.

These two conditions may, of course, be determined either by testing or by calculation from formulas found in any standard work on strength of materials. On typical formula is found in -Roark, Formulas for Stress and Strain (2d. ed. 1943), Table 8, page 152:

M =0.3183 WR (Equation 1) where:

M =bending moment, in.-lbs.

W=load, lbs.

\R=radi-us from center of ring to central axis of metal,


The ring is then checked for strength in tension by the usual formula:

S =W/ 2a (Equation 3) where:

S =tensile stress, p.s.i.

W=load, lbs. a=cross-sectional area of tranverse section of ring, in.

In a typical embodiment of the present invention, a ring (as at 12 in FIGURE 1) was designed for a load of ISO-lbs. Using A-36 steel for the ring of y -inch diameter material, and formed into a ring having a diameter of 2 -inches between center lines of metal section (FA-inches inside diameter), calculations and tests showed the ring would reliably deform under a load of ISO-lbs. but was still well below the breaking point. Accordingly, with this ring as at 12 or 23 and 24, it will be appreciated that an attempt to force open a door or window will succeed only in deforming the ring. Thus, by selectively controlling the strength of these rings 12, or 23 or 24, an attempted illegal entry of a door or window secured by the security apparatus of the present invention will be safely resisted by the controlled deformation of the rings which will absorb sudden impacts as well as provide indications that such an entry had been attempted.

What is claimed is:

1. Apparatus adapted for selectively restraining a door operatively hung in an opening in a wall and comprising: a closed metal ring adapted to pass over a door knob and having a uniform transverse circular cross-section selected in accordance with the yield strength and ultimate strength of said metal so that, upon application to said ring of opposed forces less than a predetermined magnitude, said ring will permanently elongate and at least partially collapse; a chain coupled to said ring and of a strength to carry tensile forces in excess of said predetermined magnitude; and means on said chain adapted for connection to an adjacent wall to limit the opening travel of a door hung therein to a specified distance whenever said ring is on a knob on that door.

2. The apparatus of claim 1 wherein said connection means include a second closed metal ring adapted to pass over a knob on a second door operatively hung in such an opening adjacent to the first-mentioned door.

3. The apparatus of claim 2 wherein said second metal ring is identical to said first-mentioned metal ring.

References Cited UNITED STATES PATENTS 878,607 2/1908 Cairns 292-264 1,744,456 1/ 1930 Ellingson 292264 X 2,199,369 4/1940 Bernstein 292262 X 2,662,571 12/ 1953 Kessler 292264 X MARVIN A. CHAMPION, Primary Examiner.

E. I. MCCA'RTHY, Assistant Examiner.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US878607 *Nov 4, 1907Feb 11, 1908Alexander CairnsDoor-check.
US1744456 *Jan 16, 1928Jan 21, 1930Elling EllingsonDoor-securing device
US2199369 *Jun 29, 1939Apr 30, 1940Ottorino BonomiDoor holder
US2662571 *May 25, 1950Dec 15, 1953Charles P KesslerSafety means for leaving doors ajar
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3836187 *May 24, 1973Sep 17, 1974Buettner LTwo-door lock device
US3853343 *Apr 16, 1973Dec 10, 1974Continental Lektroniks CorpBurglarproof chain guard
US4079972 *Sep 10, 1975Mar 21, 1978Hagopian Wayne NPortable door bar
US4281865 *Nov 16, 1979Aug 4, 1981Nicholson James AInterior door security
US4478442 *Sep 30, 1982Oct 23, 1984Martin Edward JSafety lock on entrance door
US4629229 *Aug 12, 1985Dec 16, 1986Frank CorrentiDoor lock device
US5501494 *Sep 12, 1994Mar 26, 1996Willetts; ThomasPortable door lock suitable for use by people of all ages
US6332344 *Dec 16, 1999Dec 25, 2001Mike MontoyaDeadbolt security chain
US6416089Jun 5, 2000Jul 9, 2002Frank James Williams, Jr.Portable door lock
US7766400 *Mar 3, 2005Aug 3, 2010Dyna Kellie PredebonDoor stay
US8313128 *Aug 20, 2009Nov 20, 2012Rhoost, Llc.Safety locking mechanism for doors
US20110042974 *Aug 20, 2009Feb 24, 2011Rhoost LlcSafety locking mechanism for doors
DE3614031A1 *Apr 25, 1986Nov 5, 1987Melchert BeschlaegeDoor chain
U.S. Classification292/264
International ClassificationE05C17/00, E05C17/36
Cooperative ClassificationE05C17/365
European ClassificationE05C17/36B