US3805121A

US3805121A - Electronic anti-theft coded combination locking system

Info

Publication number: US3805121A
Application number: US00244678A
Authority: US
Inventors: G Goldman
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-11-18
Filing date: 1972-04-17
Publication date: 1974-04-16
Anticipated expiration: 1991-04-16
Also published as: FR2207515A5; DE2256689A1

Abstract

An electronic anti-theft code combination locking system operable only by personnel knowing the code number which provides entry. The system includes first and second identical groups of multi-contact selector switches, each switch being settable to any one of a series of numbers or other symbols to effect a switch closure. The first group is disposed at a generally accessible location whereas the second group is at an inaccessible location. The first and second groups of switches are interconnected to produce a series circuit defined by the connections of all switches in both groups, the series circuit being closed only when the settings of the first group match or complement the settings of the second group. The numbers at which the switches of the first group are set to effect the closed circuit, constitute the code number. The series circuit is interposed between a power source and an electrically-actuated locking mechanism which is activated only when the series circuit is closed.

Description

United States Patent [191 Goldman [451 Apr. 16, 1974 [22] Filed:.

[ ELECTRONIC ANTI-THEFT CODED COMBINATION LOCKING SYSTEM [76] lnyentor: Gerald M. Goldman, Knoll Wood Extension, Elmsford, NY. 10523 Apr. 17, 1972 21 Appl. No.: 244,678

Related U.S. Application Data [52] U.S. Cl. 317/134, 200/44 [51] Int. Cl. H0111 47/00, HOlh 27/06 [58] Field of Search 70/277, 278; 200/43, 44,

[56] References Cited UNITED STATES PATENTS 3,760,131 9/1973 Ford et a1. 200/43 3,340,409 9/1967 Probert et a1... 317/134 X 3,317,904 5/1967 Clay 200/44 X 2,806,911 9/1957 l-larty et al.. 200/43 2,819,770 1/1958 Gibbs 70/278 X 1,923,968 8/1933 Chase 70/278 3,415,087 12/1968 Kramasz et a1. 70/277 Primary Examiner-Joseph l-l. McGlynn Assistant Examiner-Richard P. Tremblay Attorney, Agent, or Firm-Robert S. Salzman [5 7] ABSTRACT An electronic anti-theft code combination locking system operable only by personnel knowing the code number which provides entry. The system includes first and second identical groups of multi-contact selector switches, each switch being settable to any one of a series of numbers or other symbols to efiect a switch closure. The first group is disposed at a generally accessible location whereas the second group is at an inaccessible location. The first and second groups of switches are interconnected to produce a series circuit defined by the connections of all switches in both groups, the series circuit being closed only when the settings of the first group match or complement the settings of the second group. The numbers at which the switches of the first group are set to effect the closed circuit, constitute the code number. The series circuit is interposed between a power source and an electrically-actuated locking mechanism which is activated only when the series circuit is closed.

6 Claims, 8 Drawing Figures ELECTRONIC ANTI-THEFT CODED COMBINATION LOCKING SYSTEM RELATED APPLICATIONS This application is a continuation-in-part of my pending application Ser. No. 199,883, filed Nov. 18, 1971, which is a continuation-in-part of the previously filed copending application for an Electronic Anti-theft System", Serial No. 864,801, filed October 8, 1969 now U.S. Pat. No. 3,631,301, issued Dec. 28, 1971.

In the copending application, a pass key, having a predetermined profile, when placed in a keyway, carries out a switching function which, in an associated logic circuit, establishes an electrical test pattern whose nature depends on the key formation or profile. Also set up in the' logic circuit is an electrical reference pattern whose nature depends on the formation of a replaceable coded reference key. This reference key is totally inaccessible from the front of the door.

The logic circuitis so arranged that if the electrical test pattern created by the pass key exactly matches the electrical reference pattern established by the reference key, an output will be generated which serves to electromagnetically unlock the locking mechanism. But if a wrong pass key is used, the patterns will be mismatched, and not only will the lock remain closed, but an alarm will be set off to call attention to this fact.

Should the proper pass key be lost and it become necessary to use another key, this does not require a new logic circuit or any other basic alteration of the system, for all that one need do is to replace the existing reference key with a fresh inset, thereby setting up a new electrical reference pattern, and to make use of a pass key having a test pattern compatible therewith.

In short, the crucial feature in thecopending application resides in a logic circuit adapted to compare a test pattern established by the users pass key when inserted in the keyway which an existing reference pattern created by the replaceable reference key, the logic circuit yielding an output to activate the locking mechanism only when the two patterns exactly match. Thus, each reference key effectively reconditions the logic circuit to render it receptive only to a pass key consonant with the insert.

SUMMARY OF THE INVENTION The main object of the present invention is to provide an electronic locking system of the type disclosed in my copending application, but having a highly simplified logic circuit avoiding the need for semi-conductor elements and making use of inexpensive switches connected in a series pattern. The logic circuit employed in the present invention involves only connections between switches, the connections therebetween being determined as a function of a key or code pattern,

thereby creating a system that is reliable and efficient in operation and yet of low cost.

In general, the electronic locking systems currently in use display complex componentry which reduces their reliability and increases their cost. Moreover, none of the presently known systems provide for setting the combination by means of a mating key as is accomplished in my earlier copending application and in the present application.

The use of a key instead of a card to produce a code combination is much more practical, since the general public is accustomed to carrying keys. Keys can be made or duplicated by any locksmith on existing machinery, whereas cards cannot be so made or duplicated. Certain systems, such as those shown in the Welsh Pat. No. 3,403,380, require that a nonconducting material be used for the card. The present systems do not have such a requirement. If a conducting card is accidently used in such systems, a potential shock hazard results. A conducting key as used in the present invention can be made to be safe. Keys present greater versatility since they can be made to have any shape or tooth configuration.

It is another object of the invention to provide a logic system for an anti-theft device that requires no expensive electronic components for the basic sensing and switching system, that is safe and free of electrical hazards and through using logic principles, is basically electromechanically constructed.

' Briefly stated, the invention deals with an anti-theft system having a first set of electrical switches disposed in a keyway portion thereof, and a second set of switches disposed in the reference combination setting section. The switches are generally of a single-poledouble-throw type, so that a logic condition may be produced, i.e., a go or no-go function is obtained depending upon the switch position. The switches of the keyway are interconnected to the switches of the combination section. First, a reference key is inserted in the combination section to set the combination switch pattern for the system. A pass-key having a corresponding or complementary formation is then inserted into the keyway, thereby creating a combination pattern in the keyway. If both combinations match, then a release condition is effected for the system.

More particularly, the present system connects the two sets of switches in series. The poles of the switches in the keyway are connected to the poles of the switches in the reference combination section. The pole points in each switch correspond to their counterpart poles in the other combination setting section. This is accomplished by pairing switches in each segment. After the switches are paired together, they are connected in series so that a mating combination in each segment will produce a conducting circuit, and a non-mating condition will be nonconducting. The position of the switches, or pole position, is determined by the profile of the keys, or the presence or absence of a tooth of a key.

OUTLINE OF THE DRAWINGS These and other objects of the invention will be better understood and become more apparent with reference to the following detailed description and drawings in which:

FIG. 1 is ablock diagram of the anti-theft system of this invention;

FIG. 2 is a schematic view of the electrical circuitry of the invention with the switches set in their proper mating pattern to accomplish a release condition;

FIG. 3 is a schematic view of the circuitry of FIG. 2 with the switches set in an alternate mating pattern to effect a release condition;

FIG. 4 is a schematic view of the circuitry of FIG. 2 with the switches set in an improper or non-mating pattern, so that a release condition will not be effected;

FIG. 5 is a schematic view of an electrical circuit embodiment featuring multi-pole switches;

FIG. 6 is an exploded view of one possible keyway configuration of this invention;

FIG. 7 is a schematic view of an alternate electrical circuit embodiment to the circuit of FIG. 2, showing a set of series circuits wired in parallel with all the series circuits open; and

FIG. 8 is a schematic view of the electrical circuit of FIG. 7 showing some of the circuits open and some of the circuits closed.

DETAILED DESCRIPTION OF INVENTION Now referring to FIG. 1, a block diagram of the antitheft system of this invention is shown. A key 2 is inserted into a combination of switches 4, having a keyway design 40 (see FIG. 6). The key 2 has a distinctive profile or tooth pattern provided by typical teeth 7 (FIG. 6). Each tooth of the key throws a switch to which it corresponds. The combination of switches 4 is connected to another combination of switches 14 as indicated by arrow 3. The combination of switches 14 can have the same construction as the set of switches 4. Likewise, key 12 which fits switches 14, may have a corresponding profile with the key 2.

The switches 9 in the reference and in the pass-key combination segments of the system are generally single-pole-double-throw (SPDT). Because the switches in each keyway are SPDT switches, a logic pattern is developed in each switch of each segment of the system, Le, a go no go condition is set up for each switch. When the combination of the set of switches 4 corresponds to the combination of the reference set of switches 14, a conducting circuit is completed, sending a signal shown by arrow 10, to the output circuit 5. Power may then be supplied to a solenoid 6 or other output device, as shown by arrow 11.

Now referring to FIG. 2, a schematic view of the circuity of this invention is shown. For the purpose of illustration only, four pairs of switches are depicted. The set of switches denominated S1 through S4 refer to those switches disposed in the'keyway 4. The switches denominated S11 through S14 are those switches disposed in the reference combination setting keyway 14.

All the switches are single-pole-double-throw (SPDT). Switches S1 through S4 each have two pole positions a and b respectively. Switch S1 has a movable armature or slider 21 which can be set either at pole position a or at pole position b. Similarly, switches S2, S3, and S4, have

sliders

22, 23 and 24, respectively, that are set in like fashion.

Switches S11 through S14 each have two pole positions and d, respectively. Switch S11 has a slider 31 that can be set either at pole position c or at pole position d. Similarly, switches S12, S13, and S14 have

sliders

32, 33 and 34, respectively, that are set in like fashion to switch S11.

Switches S11 through S14 are set by key 12 inserted into the reference combination keyway 14.

Switches S1 through S4 are set by key 2 inserted into keyway 4. Key 12 will position

sliders

31, 32, 33, and 34 in either of their two pole positions 0 and d, respectively. The pass-key 2 will position

sliders

21, 22, 23, and 24, in either of their two pole positions a or b, respectively.

The circuit of FIG. 2 shows each of

sliders

21, 22, 23 and 24 in their a position, and each of

sliders

31, 32, 33 and 34, in their c pole position, respectively. Pole position a corresponds with the pole position 0, Le, they are conductively linked together. Pole positions b and d correspond, and are conductively linked.

Since corresponding pole positions a and c are all thrown in the circuit depicted in FIG. 2, a conducting series circuit has been created. Thus, current will be made to flow from input point 20 to output point 30. This current flow will activate the output circuit 5 as shown in FIG. 1. FIG. 3 shows an alternate conducting configuration as compared to the one shown in FIG. 2. In the circuit of FIG. 3 poles b and d match for switches S1 and S11, and for S3 and S13, while poles a and 0 correspond in switches S2 and S12 and switches S4 and S14, as shown.

Matching keys will throw the switches in each keyway to their corresponding pole positions to complete a conducting circuit configuration. The presence or absence of a tooth on the respective keys determines the pole position for the switch it services.

Keys that do not mate or match will produce a nonconducting circuit configuration like the one shown in FIG. 4. In this circuit configuration, switches S1 through S4 are all in their a pole position. However,

only switches S12 and S14 are in the matching pole position c. Since switches S11 and S13 are in noncorresponding pole position a, a non-conducting or open-circuit configuration is produced and the locking solenoid will not be energized.

The switches in this circuit can be of the type where a key must remain in the keyway to maintain the setting of the switches, or of the type where the the switches remain set and the key can be removed. Many variations in the circuitry and the keys can be made. For example, if the pole positions are inverted, i.e., pole a now corresponds with pole position d, and b corresponds with c, mating keys will new feature an inverted image with each other. In other words, where the first key has a tooth, the second key will be blank, and vice versa, so that to operate the lock, the combination setting or reference key and the pass-key are complementary.

Another variation can be made by pairing different switches together, viz., S1 and S14, S2 with S13, etc., etc. Other pairing combinations are of course possible. An inverted pairing of the switches will also change the tooth configuration of the keys that will produce a matching combination, wherein the keys will not appear identical with each other.

Other modifications in the circuitry may include the use of contacts in place of switches in some cases. An alarm circuit can be incorporated so that a nonconducting configuration (wrong key) will activate a warning signal.

The set of switches in segments 4 and/or 14 (switches S1-S4, and/or switches S11-S14) may have the mechanical configuration shown in FIG. 6. A key 2 having discrete profile teeth 7 is inserted into a series of switches 9 shown here in an exploded view. The key fits the switches 9 through keyway 40, having teeth slots 41. The switches are stacked or ganged together, and held in place by two rods extending through holes 19 in each switch. The switches 9 have an outer stationary piece 18 held in place by rods 49 as aforementioned,

and an inner rotating piece 8. Both

pieces

8 and 18 are non-conducting, and respectively, have keyway 40 with teeth slots 41 for the passage of key 2. If a tooth 7 is present at any tooth slot 41 of any disc 8, it will cause disc 8 to rotate in sleeve 18 when the key is turned as shown by arrow 50. Since all the switches 9 are constructed the same way, the rotation of each disc 8 is dependent upon its corresponding tooth 7. If a particular switch 9 sees no tooth from the key 2, then its disc will not be made to turn.

Each switch 9 has three contacts, 43, 43a, and 43b, respectively. Contact 43 corresponds to the common pole point of the SPDT switch.

Contacts

43a and 43b, respectively, correspond to the end poles of the switch. Disc '8 has a sliding contact band 48 which makes contact with either combination (43, 43a) or (43, 43b) as it rotates. In the initial or unturned condition, band 48 will make a circuit between

contacts

43 and 43a. In the rotated position, band 48 of disc 8 will make a circuit between

contacts

43 and 43b. The teeth on the key 2 are positioned to contact only the disc portion of each switch. If any tooth is made too large so that it extends into slot 41 of any stationary piece 18, the key will not be able to turn, and the whole set of switches will not be caused to operate. It has been found, however, that the tolerances are not very great for a normal keyway having between 10 and switches. As a result, the possibility of tooth overlap is not a problem.

When a tooth is not present, the base of the key profile 51 will rotate within hollow 40 of its corresponding disc 8, causing a non-rotating condition for that disc. In other words, if no tooth is present for that particular switch, a circuit will be had between

contacts

43 and 43a.

When a tooth is present, it will fit within slot 41 of disc 8 for that particular switch 9 and cause the disc 8 to respond when the key is turned. When the key is rotated, the disc 8 will turn in the same direction as the key. A limiting pin 44 is anchored in disc 8 and prevents overshooting of the disc within stationary sleeve 18 by means of slot 42 in which it rides. This insures positive contact of band 48 with contacts (43, 43a) or (43, 43b), respectively.

Band 48 corresponds to the sliders of the electrical circuitry shown in FIGS. 24.

Poles

43a, and 43b, respectively, correspond-to individual poles a and b or poles c and d of these Figures.

The nice feature of the design is that each switch 9 is made the same, and each set of switches for the passkey and reference key is also the same, thus reducing manufacturing costs. Also, it will be seen from FIG. 6, that the switches are completely enclosed, and never see contact with the key. The keyway presents to the observer looking into the keyway, a smooth, flat surface with no contacts.

Since each keyway for every lock is the same, every keyway looks the same, so that no information is given to someone trying to intrude. Also, if a keyway is removed from its door, only dangling wires will be seen by the intruder. He will have no way of correlating how to match all the wires to produce a conducting circuit, since the combination of switches in the reference keyway is inaccessible to his view, i.e., the reference keyway is hidden behind the door, or another inaccessible partition out of the reach of the intruder. A hot lead may be introduced amongst the leads to the switches for the purpose of blowing the circuit if attempts at shorting them are made.

It is evident from the foregoing, that a superior system has been developed that meets all the objectives aforementioned. Each switch may be molded of nonconducting plastic except for the contacts or slider portion. Since the switch keyway is of basic nonconducting construction, no shock hazard is ever introduced.

Contracts

43, 43a, and 43b may need no wiring if snapped into a circuit board, or the switches 9 may themselves be made as a circuit board having parts receptive to key positions, with each circuit board (switch 9) being ganged to the next circuit board (switch 9). This latter scheme would have both

keyway circuits

4 and 14 on the same board already connected to each other.

Another variation of the circuitry shown in FIG. 2 is illustrated in FIGS. 7 and 8.

Sliders

21, 22, 23 and 24 of switches S S S and S respectively, are wired together.

Sliders

31, 32, 33 and 34 of switches S S S and S respectively, are wired together. The circuit depicts a set of series circuits wired in parallel. In FIG. 7,

sliders

21 and 23 are in their b pole position, respectively, and

sliders

22 and 24 in their a pole position, respectively.

Sliders

31 and 33 are in their d pole position, respectively, and

sliders

32 and 34 are in their 0 pole position, respectively.

Since poles a and d are wired together, and poles b and c are wired together, none of the series circuits wired in parallel carry current, i.e. none of the switch combinations S and S 8 and S 5,, and S, and S and S form closed series circuits. This open-series circuits condition is the result of matching or complementary pass-key and reference key profiles, which have set the proper corresponding switches. With all the series circuits open, current will flow from the input 20 to the output 30.

Keys that do not match or correspond will produce a circuit where some or all of the series circuits will be closed as shown in FIG. 8. In this circuit configuration, switches S, through 5., are all in their a pole position, respectively. However, only switches S and S are in the matching pole position c. Since switches S and S are in non-corresponding pole position d, a conducting circuit configuration (short circuit) is produced. Current will now flow from input 20 to ground 40, shorting out the output 30. Resistor R in FIGS. 7 and 8 is a current-limiting resistor. To overcome the current limitation due to resistor R, amplification may be required on the output.

The above circuit may be generally described as an electrical circuit for an output-controlled mechanism operable by personnel carrying a pass-key having a profile which matches or complements the profile of a reference key. The output is operable only when a signal is applied to it. The keyway for the pass-key has a first group of switches which are selectively actuated by insertion of the pass-key to create test switching connections. A combination setting device is installed at a generally inaccessible position, and contains a second group of switches which are selectively actuated by the reference key to create reference switching connections. The reference switching connections are dependent on the profile of the reference key, and the test switching connections are dependent on the profile of the pass-key. Means are provided to interconnect the first and second group of switches to produce a set of series circuits wired in parallel; the series circuits defined by said test and reference connections. The series circuits are electrically open only when the inserted pass-key matches or complements the reference key. Otherwise, some or all of the circuits will be closed. A signal will be produced at the output only when all of the series circuits are open.

Another embodiment of the invention is depicted in FIG. 5. This embodiment proposes the replacement of all the SPDT switches with multi-pole rotary switches having, for example, pole positions. Of course, these rotary switches may have any number of poles and/or throws. In this circuit, switch S has been replaced by switch A switch S has been substituted for switch 8,, etc., etc. In order for this circuit to produce a conducting configuration, corresponding poles must again match. Therefore, pole position 6 of A must match pole 6 of B and pole position 3 of A must be matched with pole position 3 of B2, etc., etc.

The embodiment may replace the keyways of FIG. 1 with two panels of rotary switches. Thus, keyway 4 will now be a panel with switches Al through An, and keyway 14 will be a second panel with switches Bl through Bn. When either panel Al An, or B1 Bn, is set in a discrete pattern, a conducting circuit will be obtained by setting the other panel in a matching pattern.

It should be noted, however, that inverted pole posi-\ tions, and inverse pairing is also possible for this embodiment as was previously mentioned. For example,

combinations

9,6,3,l,0,5, in the first panel may correspond to the inverted setting 5,0,l,3,6,9, in the second panel. I

A time generated combinated can be designed where several (or all) of the combination reference portion switches can be set by a timing mechanism. Thus, the releasing combination will change with time, or become inert untila certain time is reached.

In hotels and motels, the circuitry may be designed so that there is an external switch in the main office that will open the door, or prevent the door from opening. The switch or switches may be wired directly to the output circuit, by-passing the keyways. The combination setting keyway can also be in the main office and wired to the keyway in the door. This will facilitate cleaning the room or allowing entrance. for loss of key.

Switches may also be activated by pushbuttons rather than a key if so desired.

While there have been shown and described preferred embodiments of an electronic anti-theft locking system, in accordance with the invention, it will be appreciated that many changes and modifications may be made therein without, however, departing from the essential spirit of the invention.

I claim:

1. An electrically-controlled mechanism operable only by personnel carrying a pass-key having a profile which matches or complements the profile of a reference key, said mechanism comprising:

a. a signal-operated output which is operable only when a signal is applied thereto;

b. a keyway whose opening is generally accessible, said keyway having a first group of switches therein which are selectively actuated by insertion of said pass-key to create test switching connections which depend on the profile thereof;

c. a combination setting device installed at a generally inaccessible position constituted by a second group of switches which are selectively actuated by said reference key to create references switching connections depending on the profile of the reference key;

d. means interconnecting said first and second group of switches to produce multiple series paths, each of said paths being defined by said test and reference connections and each being electrically open paths only when the inserted pass-key matches or complements the reference key, some or all of the paths otherwise being closed; and

e. means to interpose said series paths between a signal source and said output to produce said signal only when all of the series paths are open.

2. A mechanism as set forth in claim 1, wherein first and second groups of switches are both constituted by single-pole, double-throw switches whose poles are caused to assume positions determined by the profile of the keys.

3. A mechanism as set forth in claim 1, wherein the combination setting device is constituted by a reference keyway corresponding to said keyway having a first group of switches whereby a signal is produced only when the profile of the inserted pass-key is identical to the profile of the reference key.

4. An electrically-controlled system associated with a solenoid and arranged to activate said solenoid only when a pass-key having a particular profile is inserted by a key holder, said system comprising:

a. a keyway mounted at a position accessible to key holders, said keyway being provided with a first group of electrical switches which are selectively activated by a pass-key inserted therein in accordance with the profile thereof to create a test switching pattern;

b. a second group of electrical switches which are mounted at a position inaccessible to key holders and which are selectively activated by a profile reference key in accordance with the profile thereof to create a reference switching pattern;

c. means interconnecting said first and second groups of switches to produce multiple series paths which are open only when the switching patterns produced by the keys are those established by keys which match or complement each other, some or all of the paths otherwise being closed; and

d. means to interpose said series paths between a voltage source and said solenoid to activate said solenoid only when all of the series paths are open.

5. A system as set forth in claim 4, wherein the switches in the first group are alternately interconnected to the switches in the second group.

6. A combination-controlled mechanism operable only by personnel possessing the combination, said mechanism comprising:

b. a first group of switches which are generally accessible and which are selectively activated by personnel possessing the combination;

c. a combination setting device installed at a generally inacessible position constituted by a second group of switches which are selectively actuated in accordance with a combination;

d. means interconnecting said first and second group of switches to produce a set of series circuits, said series circuits defined by pole positions of the first and second switches, some or all of the series circuits normally being electrically closed, and passe. means interposing said series circuits between a ing a signal only when the combination of the first group of switches matches or complements the combination of the second set of switches, all of the series circuits then being open; and

signal source and said output to produce said signal when all of the series circuits are open.

Claims

1. An electrically-controlled mechanism operable only by personnel carrying a pass-key having a profile which matches or complements the profile of a reference key, said mechanism comprising: a. a signal-operated output which is operable only when a signal is applied thereto; b. a keyway whose opening is generally accessible, said keyway having a first group of switches therein which are selectively actuated by insertion of said pass-key to create test switching connections which depend on the profile thereof; c. a combination setting device installed at a generally inaccessible position constituted by a second group of switches which are selectively actuated by said reference key to create references switching connections depending on the profile of the reference key; d. means interconnecting said first and second group of switches to produce multiple series paths, each of said paths being defined by said test and reference connections and each being electrically open paths only when the inserted pass-key matches or complements the reference key, some or all of the paths otherwise being closed; and e. means to interpose said series paths between a signal source and said output to produce said signal only when all of the series paths are open.

4. An electrically-controlled system associated with a solenoid and arranged to activate said solenoid only when a pass-key having a particular profile is inserted by a key holder, said system comprising: a. a keyway mounted at a position accessible to key holders, said keyway being provided with a first group of electrical switches which are selectively activated by a pass-key inserted therein in accordance with the profile thereof to create a test switching pattern; b. a second group of electrical switches which are mounted at a position inaccessible to key holders and which are selectively acTivated by a profile reference key in accordance with the profile thereof to create a reference switching pattern; c. means interconnecting said first and second groups of switches to produce multiple series paths which are open only when the switching patterns produced by the keys are those established by keys which match or complement each other, some or all of the paths otherwise being closed; and d. means to interpose said series paths between a voltage source and said solenoid to activate said solenoid only when all of the series paths are open.

6. A combination-controlled mechanism operable only by personnel possessing the combination, said mechanism comprising: a. a signal-operated output which is operable only when a signal is applied thereto; b. a first group of switches which are generally accessible and which are selectively activated by personnel possessing the combination; c. a combination setting device installed at a generally inacessible position constituted by a second group of switches which are selectively actuated in accordance with a combination; d. means interconnecting said first and second group of switches to produce a set of series circuits, said series circuits defined by pole positions of the first and second switches, some or all of the series circuits normally being electrically closed, and passing a signal only when the combination of the first group of switches matches or complements the combination of the second set of switches, all of the series circuits then being open; and e. means interposing said series circuits between a signal source and said output to produce said signal when all of the series circuits are open.