US3024452A - Multi-digit electrical door lock - Google Patents

Description

March 6, 1962 E. J. LEONARD 3,024,452

MULTI-DIGIT ELECTRICAL DooR Loox Filed Aug. 22, 195e 2 sheets-sheet 1 ATToR'N Evs EDWARD J. Laonmrz March 6, 1962 E. J. LEONARD 3,024,452

MULTI-DIGIT ELECTRICAL DOOR LOCK Filed Aug. 22, 1958 2 Sheets-Sheet 2 FKa. 4

BIO

Y INVENTOR. o EDWARD J. LEONARD BY ifw, @644/74 @ad ATTORNEYS United States Patent f 3,024,452 MUL -DlGlT ELECTRHCAL DOOR LOCK Edward Ii. Leonard, Chicago, Ill., assigner to International Telephone and Telegraph Corporation, a corporation of Maryiand Filed Aug. 22, 1953, Ser. No. 756,591 Claims. (Cl. S40-274) This invention relates to a multi-digit electrical door lock. lts principal object is to provide a rnulti-digit electrical door lock of great security against the door being unlocked by anyone other than an authorized person who knows the currently-assigned multi-digit unlocking number.

lt is generally conceded that multi-digit combination locks are more secure against being opened by 'unauthorized persons than are the usual key-operated locks. The usual combination locks, however, are not entirely satisfactory where great security is important. Among other reasons, changing the combination, as when it is suspected that unauthorized persons may have learned the combination or when previously authorized persons are no longer authorized, is usually a time-consuming operation which often requires the services of a trained locksmith, wherefore the combination is frequently left unchanged too long.

Moreover, the ordinary combination lock may sometimes be opened on repeated trials by unscrupulous persons who have become expert in such a procedure.

According to the invention, the foregoing and other disadvantages of prior devices are overcome by providing a multi-digit electrical door lock so arranged that the cornbination may be changed readily from time to time as desired by merely altering electrical connections, as by rotating each of a number of digit switches to respective positions corresponding to the digits of the desired new combination.

Further, according to the invention, hunting for the combination by trial digit transmission is thwarted, in that any attempt at digit transmission which fails to coincide with the currently assigned combination establishes a locked condition which disables the lock from opening and sounds an alarm, such locked condition being maintained until cleared, as after an investigation has been made.

Conveniently, the digits of any desired combination assigna'ble to the lock are imparted to the control meche anisrn by a single set of digit keys or pushbuttons which rnay be mounted outside the door controlled by the lock. A feature of the disclosed circuit arrangement is that the lack of knowing the combination cannot be circumvented by opening the pushbutton set and effecting connections between the then exposed conductors connected thereto.

According to a further feature, the successive digits of the combination must be transmitted with no undue delay between digits, failing which timing interval elapses to cancel the portion of the combination already sent and to require a complete new sending of the combination. This timing feature is employed to limit the unlocked interval, thereby barring entry if the one seeking entrance delays opening the door for more than a predetermined comparatively short interval after having sent the correct complete combination.

According to a further feature of the invention, an alarm is sounded if the door is held open for more than a predetermined interval, thereby guarding against an authorized person accidentally or otherwise leaving the door open and unlocked to permit entry of unauthorized persons. A related feature is that the door-open alarm may be cut off when desired, as when apparatus or equipment is required to be moved through the door over an 3,024,452 Patented Mar. e, 1962 ICC extended period, in which case a warning signal is given, at any desired location, that the area reached through the door is temporarily unguarded.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent, and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, comprising FIGS. l to 4, wherein:

FIG. l is a general plan View of an application of the invention to an area protected by a door having a combination door lock according to the invention;

FIGS. 2 and 3 show in circuit diagram the electrical apparatus indicated in FIG. 1; and

FIG. 4 shows a modification of the digit apparatus of FlG. 2.

FIG. l shows a plan diagrammatic view of the invention being applied to a door which gives access to a protected area PA. The door 100 is illustrated as being hinged to open inwardly into area PA and may be provided with the usual illustrated turnable door knobs `for opening the door, the outside knob being understood t0 be ineffective unless the ldoor lock DL is electrically actuated to permit the `door to be opened from the outside.

The principal controlling apparatus for the electrical door lock is contained within the closed compartment 110, to which the door lock DL is connected by conductors 102. A set of pushbuttons PB is shown mounted on the wall outside of door 100, being the pushbuttons PB illustrated in circuit diagram in FIG. 2. Buttons PB are connected to apparatus by conductors 101. Alarm AL, connected to 110 by conductors 105 is provided to sound an alarm when the occasion arises, as when any unassigned combination is used in an unauthorized attempt to unlock door 160. Release key RK, connected over conductors 104, may be employed to release such an alarm condition. RK may be in a control area CA as indicated, or at such location as may be deemed best for any given installation.

Door 100 is provided with door switch DS, connected to apparatus 110 over conductors 103 to cause alarm AL to be operated if the door 100 is held open longer than a predetermined timed interval. The door-open alarm condition may be disconnected at cut-off device CO when desired, in which case warning light WL is lighted, the circuit arrangement being as shown in FIG. 3.

Pushbutton set PB of FIG. 1 is shown in circuit diagram in FIG. 2 as a set of ten pushbuttons, or equivalent automatically restoring switches 1 to 9 and 0. Each pushbutton of set PB includes a pair of normally open contact sets, closable upon actuation of the pushbutton. Each button is thus adapted to send either one element or two elements of a `four-element code employed for transmitting the ten digit values corresponding respectively to the buttons of set PB. Alternating current delivered from power conductor Pl, over conductor P in group 101, is rectified at the oppositely directed rectiiers 203 for delivery over posi-tive conductor 201 and negative conductor 262 to the pushbuttons, whence it may be applied (according to the button pushed) over either or both `of the conductors T and R in group 101.

Four polarized code element relays CA to CD are provided within apparatus -1r10 of FIG. l to respond singly or in combination according to which of the buttons 1 to 0 of set PB is actuated. Relays CA and CB are connected in series between conductor T and the return `alternating current conductor P2, while relays CC and CD are connected in series between conductor R and conductor P2. Relays CA and CC are positively polarized by their respective illustrated shunting rectiers, and conductors CB and CD are similarly negatively polarized, Wherefore any relay CA to CD responds only when current of the indicated polarity is delivered over its associated circuit.

Digit relays DA to DD are controlled respectively by polarized relays CA to CD.

FIG. 2 also shows door lock DL of FIG. 1 in the form of a conventional solenoid, and it shows door switch DS of FIG. 1 in the form of a normally closed switch which opens upon door 100 being opened from its illustrated closed and locked position, and remains open until the door is again closed and locked.

FIG. 3 shows transformer 302 which receives energizing current from supply conductors 301 and supplies 50- volt `alternatingcurrent power to conductors P1 and P2. Rectiers 303 provide full-wave rectification from conductors P1 and P2 to the positive and negative conductors 304 extending to the illustrated direct-current apparatus. The positive one of these conductors is shown grounded. Each connection of that conductor is indicated in the circuit diagram as a conventional ground symbol. Each connection of the negative one of the conductors 304 is indicated in the circuit diagram by a terminal with the negative sign applied thereto.

FlG. 3 further shows the digit assigning apparatus cornprising switches DS1 to DS3 Whereat connections are made between selected digit conductors D (controlled by relays DA to DD of FIG. 1) and the digit-receiving relay apparatus, to the right of the digit switches, according to any desired one of one thousand digit combinations.

The digit-receiving apparatus comprises digit-responding relays D1 and D2 which operate in combination with each other and with transfer relay TR to eifect unlocking of the door responsive to receipt of the currently assigned combination. Interval-timer relay IT times the intervals between successive digits, together with the unlock interval following the final digit of the combination, during which the door may be opened. Guard relay G, controlled over guard conductor GC from FIG. 2, controls alarm relay ALR to sound an alarm responsive to any digit not conforming to the assigned combination. Doortimer relay DT is normally held energized by door switch DS of FIGS. 1 and 2.

FIG. 3 also shows alarm device AL and release key RK of FIG. 1, along with cut-off key CO and warning light WL.

Selting the Combination With the system installed as shown, any desired one of the one thousand three-digit combinations (111 to 000) according to which of the buttons in set PB may be operated to unlock the door 100, is assigned at individually rotatable digit switches DS1 to DS3. If the combination 3, 6, 1 is desired, the digit switches are individually rotated from such positions as they may occupy to the respective positions shown in FIG. 3. Then, switch DS1 is on its third terminal, in contact with wire 3 in digit group D; D52 is on its sixth terminal, in contact with wire 6 in group D; and switch DS3 is on its first terminal, in contact with wire 1 of group D. When a different combination is desired, one, two or all three, of the switches DS1 to DS3 are merely moved to accord with the respective digits of the desired new three-digit combination.

Unlocking Operation With the door 100 of FIG. l in its normally'closed position, an authorized person wishing admittance to protected `area PA need only operate the pushbuttons PB in accordance with the respective digits of the currently assigned three-digit combination, which may be assumed to be the number 361, in accordance With the respective digits of which digit switches DS1 to DS3 are illustrated as being positioned. For this purpose, buttons, 3, 6, and 1 of set PB are actuated momentarily, one at a time, in

the indicated succession to cause the solenoid of door lock DL to become energized temporarily to unlock the door 100. Responsive to each of these pushbutton operations, the corresponding combination of code relays CA to CD is operated in accordance with the code shown in the following code table:

Code Table A B C D X X X X X X X X X X The relays P-A to PD correspond respectively to the clements A to D in the above code table, and tne letter "X is used for each digit wherein any such code element appears.

It will be observed from the `above code table that the digits and corresponding pushbuttons have assigned thereto the `following code combinations respectively, considering the digits in their indicated order from l to 9 and 0: A, B, AB, C, AC, BC, D, AD, BD, and CD. It will be understood, of course, that any desired other orders of assignment of code combinations may be employed in place of the one specically given.

First Digit When button 3 of group PB of FIG. 2 is actuated in accordance with the first digit "3 in the currently assigned combination, it connects each of the polarized con ductors 201 and 202 to conductor T in group 101, thereby supplying effectively unrectified current over conductor T and through relays CA and CB in series, to the return power conductor P2. Relay CA receives current on each positive half cycle over conductors P1 and P2, and relay CB receives current on each negative half cycle. Relays PA and PB thus both operate at very nearly the same time, the initial current to one relay being time-displaced less than nine milliseconds from the initial current to the other relay. During the time that either such relay is not receiving current directly while the button remains pushed, a local circulating current continues therethrough by way of the shunting rectifier of the relay, as a consequence of which both relay PA and PB remain operated continuously for as long a time as button 3 remains actuated.

Digit relays DA and DB both operate responsive to operation of their respectively associated relays PA and PB. Contacts 1 of relays DA and DB ground guard conductor GC (in common with relays DA to DD, when operated), thereby closing a circuit through back contacts 1 of relays D1 and D2 for guard relay G. Contacts 1 of relay G lock ground on guard conductor GC through contacts 2 of ALR, whereby relay G remains operated independent of relays DA to DD. Contacts 2 of relay G close a circuit for alarm relay ALR to ground over conductors 104 and release key RK. Relay ALR is slowoperating and. consequently, has its circuit interrupted by the hereinafter described operation of relay D1 and the consequent release of relay G when (as currently assumed) the relays of FIG. l have received a pushbutton setting in accordance with the assigned unlock combination.

Referring further to the noted operation of digit relays DA to DD, it will be observed that ground applied to the apex of the illustrated contact pyramid of these relays is normally maintained disconnected from all of the ten wires 1 to 0 in digit group D by contacts of these relays. With any one, or any combination, of the relays DA to DD operated, the marking ground can be placed on no more than one of the wires 1 to (l of D. With relays DA and DB now operated as assumed, ground is applied to digit conductor 3 of group D, the grounding path through back contacts 2 and 3 of relays DD and DC, and front contacts 5 and 7 of relays DB and DA, to conductor D3.

The ground thus placed on conductor 3 of group D traverses the brush of the rst digit switch DS1, thereby closing a circuit through back contacts 5 and 3 of relays TR and D2 for the lower winding of digit relay D1. Relay D1 thereupon operates. At its front contacts 2, it operates interval-timer relay IT through back contacts 2 of relay D2, at the same time discharging the normally charged timing condenser 305 through resistor 166. Relay D1 is locked to ground through its own lower winding and the lower winding of D2, through front contacts i and 1 of D1 and IT, and back contacts 3 of ALR, but no substantial current iiows over this locking circuit as long as the initial circuit for relay D1 remains established, over DS1. Back contacts 1 of relay D1 opencircuit and restore guard relay G, which open-circuits alarm relay ALR before that relay has had time to operate.

Relay D1 remains operated, and D2 remains restored, until the actuated pushbutton (3 of set PB) is restored, whereupon relays CA and CB restore, permitting relays DA and DB to restore. Conductor GC and conductor 1 of group D are thereby ungrounded. The initial circuit of the lower winding of relay D1 is thereby opened, leaving relay D1 operated in its described locking circuit, in which circuit relay D2 now operates to mark the end of the transmission of the irst digit of the combination. Back contacts 2 of D2 open the operate circuit of intervaltimer relay IT, leaving that relay operated in the recharge circuit of the now-discharged condenser 395, for a maximum interval of perhaps five seconds, during which the correct second digit of the combination must be received to prevent relay IT from restoring and clearing out the digit record. Front contact 1 of D2 again connects the winding of relay G to conductor GC, through front contacts 1 of D1. Contacts 5 of D2 disconnect the brush of switch DS1, which has now served its purpose in receiving the first digit marking, and contacts 3 of D2 connect the brush of D32 in circuit preparatory to the receipt of the second digit (6 in the illustrated example) of the currently assigned combination.

Second Digit When pushbutton 6 of set PB is actuated to send the second digit (6) of the assigned combination, it connects the positive and negative half-cycle conductors 201 and 262 respectively to conductors R and T of group 101. Negative polarized relay CB is responsively operated over conductor T, and positive polarized relay CC is operated over conductor R, according to the code BC indicative of the digit 6. Digit relays DB and DC responsively operate, grounding conductor GC to reoperate guard relay G, this time through front contacts 1 of DI, D2, with results as described. CB and CC also place ground on conductor 6 of group D at their front contacts 4 and 3, the grounding path including back contacts 2 and 5 of unoperated relays DD and DA. Ground on 6 of group D closes a circuit through the second digit switch DS2, and thence through contacts 3 of D2 for the upper winding of D2, whereby D2 vis held operated during the remainder of the seconddigit transmission. A branch path energizes the upper winding of relay DI, through contacts 1 of TR and 3 of D1. Diterential relay D1 is thereby magnetically neutralized and restored. Its previous locking circuit is opened at its front contacts 4 (leaving D2 dependent upon its upper winding), and the upper winding of D1 is disconnected at contacts 3 of D1. The still-operated interval-timer relay IT is reenergized, and condenser 305 is again discharged, this time through back contacts 2 of D1 and front contacts 2 of D2. Guard relay G is again disconnected and restored, this time at front contact 1 of D1.

Upon D1 restoring, with D2 held operated, transfer relay TR is now operated through contacts 4 of D1 and D2, its operating circuit further including contacts 1 and 3 of IT and ALR. At its contacts 2, TR locks operated independent of contacts of D1 and D2, but with no other immediate result, since operation of TR contacts 1, 3, and i is merely preparatory for the moment.

When transmission of the second digit is ended, by restoration of button 6 of PB, relays CB and CC responsively restore, restoring DB and DC to again unground conductors GC and D6. The circuit path through DS2 for holding the upper Winding of D2 is thereby opened, whereupon D2 restores and disconnects from DSZ.

Relays D1 and D2 are now both again in restored condition, and transfer relay TR stands locked operated. The energizing circuit of interval-timer relay IT is again opened, this time at front contacts 2 of D2 to set a time limit on the interval permitted between the second and third digits of the combination. Moreover, guard relay G is reconnected at back contacts 1 of D1 and D2 preparatory to checking the correctness of the third digit, when received.

Third Digit When the third digit l is transmitted, by actuation of pushbutton 1 of PB, current of positive polarity from 261 is transmitted over conductor T, opera-ting relay CA, which operates DA. GC is again grounded, to operate relay G for the third time with results as described. DA also grounds conductor 1 of D at its contacts S, by Way of back contacts 5, 3, 2 of DB, DC, DD. A circuit is thereby closed through the brush of third digit switch DS3, and thence through front contacts 3 of TR and back contacts 5 of D2, for reoperating D1 through its lower winding. Thereupon D1 again looks operated through its front contacts 4, as described; it reenergizes IT at its front contacts 2; and it again open-circuits and restores G at its back contacts 1.

When transmission of Ithe third digit is ended, and relays CA and DA have restored, the consequent ungrounding of digit conductor 1 of D ungrounds the brush of DS3 to open the operate circuit of D1. That relay, however, again remains operated in its local locking circuit, wherein relay D2 again reoperates, again opening the energizing path of relay IT, this time to set a time limit on the unlocking interval permitted for opening the door 16)` of FIG. 1.

Now, for the first time during the operations being described, all three of the digit-checking relays D1, D2, and TR stand operated at the same time.

Unlocking and Clearing Ont Ground is now extended through contacts 5 of relay D1, by way of contacts 6 and 4 of D2 land TR, and over conductors 102, to energize the solenoid of door lock DL, whereby the door (160 of FIG. l) looked by DL is unlocked during the interval that DL is energized. During that interval, of perhaps five seconds, door may be opened.

During the interval that relays D1, D2, and TR are all operated and held operated through front contacts 1 of IT, no further digit transmission from PB can be effective over digit conductors D- and switches DS1 to DS3. DS1 and DS3 are disconnected at contacts 5 of D2 and DSZ is disconnected from D1 at contacts 1 of D1. The existing connection of D52 to the upper winding of D2, at 3 of D2, is immaterial because D2 is already operated.

When the described unlocking circuit over conductors lil-2 has been closed for about live seconds, intervaltimer relay IT restores responsive to condenser 305` becoming recharged therethrough. IT open-circuits and 7 restores relays D1, D2, and TR, returning the combination-recording apparatus to normal and opening the described circuit over conductors 102 for door lock DL. If the door (100 of FIG. l) is still in closed position, it immediately relocks. Otherwise, it relocks upon being closed.

Door-Open Alarm When the door 100 is open, either for entry to or exit from `the protected area, door switch DS of FIGS. l and 2 opens, thereby opening the normally closed circuit over conductors 103 for door-timer relay DT. Relay DT is shunted by condenser 307 in series with limiting resistor 308. It is maintained operated in the discharge path of 307 for a selected interval, such as ten seconds, long enough for an authorized person (or a small group) to pass through the door. Usually, the opened door is thereafter reclosed to reenergize DT before DT has had time to restore. However, if the door is left open beyond the short interval permitted, relay DT restores when condenser 307 has effectively discharged therethrough. Thereupon, it closes a circuit through its contacts 1, and closed contacts of CO, over 105 for the alarm bell AL, thereby sounding an alarm. Such alarm continues to sound until the door is reclosed, whereupon relay D1 is reenergized over conductors 103 to open the alarm circuit.

If the door is required to be held open for longer than the timing interval, as for the entry of furniture or equipment, for example, the door-controlled circuit of alarm AL may be opened by operation of key or switch CO, which disconnects the door-open alarm circuit and lights warning light WL as a signal that the door-open alarm is disconnected.

Sending-Gap Clearozlt If, at any time during the sending of the digits of the currently assigned three-digit combination, the sender neglects to push the button for the next digit for more than the five seconds or so that IT will remain operated in the described recharging circuit of condenser 305, relay IT restores and releases any operated ones of digit recording relays D1, D2, and TR. The apparatus is thereby cleared out in readiness for a new code transmission.

Wrong-Combination Alarm When the wrong digit combination is transmitted from PB, which is any combination differing in one or more digits from the combination currently assigned at switches DS1, DS2, DS3, alarm relay ALR is operated responsive to the first transmitted digit (first, second, or third) which differs from the corresponding digit of the assigned com bination. It has been described that guard relay G is operated over guard conductorGC and locked each time any one of the relays DA to DD responds to a digit sent from a button of set PB. It has been further described that relay G is almost immediately disconnected and restored by relay D1 for each received digit of the assigned combination, before slow-operating relay ALR has had time to operate. For example, the described operation of relay D1 on the first digit and again on the third digit, disconnects relay G at back contacts 1 of D1, relay D2 than being in restored condition. The described disconnection of G on the second digit (with relay D2 being held operated) occurs at front contacts 2 of D1 on the forced release of D1.

When any transmitted digit (either the first, second, or third) fails to be the corresponding digit of the assigned combination, the currently connected one of the digit switches DS1 to `DS3 then fails to carry current to the concerned winding (lower or upper) of D1, wherefore D1 fails to respond, leaving relay G operated over GC. The circuit of ALR thus remains closed over conductors 104 and through contacts 2 of relay G for a sufhcient interval (such as twenty-five milliseconds) for slowoperating relay ALR to operate. Upon operating, relay ALR locks operated at its contacts 2 independent of contacts 2 of relay G. Contacts 1 of ALR open the locking circuit of G. At its back contacts 3, relay ALR clears out all operated ones of relays D1, D2, and TR, restoring IT and relay G, unless a button of PB is being held operated. Front contacts 3 of relay ALR energize alarm AL over conductors 105, thereby sounding an alarm.

When the alarm condition has been suitably investigated, release switch or key RK is temporarily actuated, open-circuiting and restoring ALR, which unlocks at its contacts 2 and opens the alarm circuit at its front contacts 3, thereby terminating the alarm condition.

Nullfcaton 0f Hunting Attempts Attempts at hunting for any one of the three digits of the currently assigned combination by actuating two or more of the ten pushbuttons of set PB, together or in succession, are nullified in the disclosed arrangement, wherein (l) the series arrangement Within the contact pyramid of relays DA to DD insures that no more than one of the ten digit conductors 1 to 0 of group B can be energized at the same time, irrespective of the num ber of pushbuttons actuated; and (2) self-locking guard relay G, which controls alarm relay ALR, locks operated on any digit transmission until relay D1 acts (operates on first and third digits and restores on the second), to thus operate the self-locking alarm relay ALR at the end of an interval too short to permit the effective actuation of a second one of the pushbuttons without relay ALR operating to lock at its contacts 2. The operation of ALR cancels any recorded information at its back contacts 1 and 3, and energizes alarm circuit 105 at its front contacts 3, as described.

For example, if relay G requires ten milliseconds to operate, and if relay D1 is so wound and adjusted that it requires a circuit closure of its lower winding for at least twenty milliseconds for its operation through switch DS1 or DS3, and a like interval of circuit-closure of its upper winding through switch D52 for its restoration, then two successive effective pushbutton operations of a hunting attempt must require a minimum of forty milliseconds of circuit closure, which exceeds the thirty-five milliseconds of effective circuit closure (ten for G, and twenty-five for ALR) required for relays G and ALR to operate successively and lock if the first effective button pushed does not coincide with the assigned combination to cause relay D2 to respond.

Referring to FIG. 4, the modification therein includes ten pushbuttons B1 to B10 (only B1, B2, and B10 being shown), which replace set PB of FIGS. l and 2, and render relays CA to CD and DA to DD unnecessary. These buttons are connected to the control apparatus by the eleven conductors 401, comprising a ground-supply conductor and ten digit conductors 1 to 0 which comprise the conductors in set D3, corresponding to set D, of FIGS. 1 and 2.

When any digit button B1 to B10 of FIG. 4 is actuated, it grounds the associated digit conductor in group D of FIG. 3, at the same time grounding guard conductor GC of FIG. 3 by way of the associated one of the diode rectifiers R1 to R10.

It will be observed that actuation of two or more buttons B1 to B10 results in ground being placed on only one digit conductor, since the ground supply is chained through back contacts of the buttons.

The modification of FIG. 4 has the economical advantage over FIG. 2 in not requiring the eight relays CA to CD and DA to DD, which is partly offset by requiring additional conductors in connecting group 401. This advantage is usually outweighed by the fact that an unauthorized person may succeed in forcing access to the wiring of the pushbutton set of FIG. 4 and thus, for example, strap together all ten digit conductors, to cause the grounding of one of them to constitute grounding all of them, thereby effectively closing a circuit through any currently connected switch DS1 to DS3 irrespective of its setting. It is clear that no such lack of security exists in the arrangement of FIG. 2, wherein the disclosed contact pyramid of relays DA to DD', not accessible from outside the protected area, is arrranged as described to preclude the grounding of more than one digit conductor at a time.

While I have described above the principles of my invention in connection with specic apparatus, it is to be clearly understood that this description is made only by Way of example and not as a limitation to the scope of my invention.

I claim:

l. A system for unlocking a lockable door, comprising an energizable unlocker, a group of digit pushbuttons and digit conductors corresponding respectively thereto, means responsive to the pushing of any pushbutton for energizing the corresponding digit conductor, a series of code conductors, code-assigning means for connecting any code conductor to any desired digit conductor for energization thereover, including means for connecting more than one code conductor to the same digit conductor, a sequence device with which the code conductors are associated and to which the iirst code conductor is normally connected, with the remaining code conductors being normally disconnected therefrom, means responsive to the energization of any code conductor preceding the last for operating the sequence device to disconnect the currently connected code conductor from the sequence device and to connect the next succeeding one thereto, and means responsive to the energization of the last code conductor when connected to the sequence device for operating the sequence device to energize the said unlocker.

2. A system for unlocking a lockable door, comprising an energizable unlocker, a group of digit pushbuttons and digit conductors corresponding respectively thereto, means responsive to the pushing of any pushbutton for energizing the corresponding digit conductor, a series of code conducto-rs, code-assigning means for connecting any code conductor to any desired digit conductor for energization thereover, a sequence device with which the code conductors are associated and to which the rst code conductor is normally connected with the remaining code conductors being normally disconnected therefrom, means responsive to the energization of any code conductor preceding the last for operating the sequence device t disconnect the currently connected code conductor from the sequence device and to connect the next succeeding one thereto, and means responsive to the energization of the last code conductor when connected to the sequence device for operating the sequence device to energize the said unlocker, the said means for energizing the said digit conductors including means for preventing the energization of more than one digit conductor responsive to the pushing concurrently of more than one pushbutton.

3. A system for unlocking a lockable door, comprising an encrgizable unlocker, a group of digit pushbuttons and digit conductors corresponding respectively thereto, means responsive to the pushing of any pushbutton for energizing the corresponding digit conductor, a series of code conductors, code-assigning means for connecting any code conductor to any desired digit conductor for energization thereover, a sequence device with which the code conductors are associated and to which the first code conductor is normally connected with the remaining code conductors being normally disconnected therefrom, means responsive to the energization of any code conductor preceding the last for operating the sequence device to disconnect the currently connected code conductor from the sequence device and to connect the next succeeding one thereto, means responsive to the energization of the last code conductor when connected to the sequence device for operating the sequence device to energize the said unlocker, the said pushbuttons being remote from the said means for energizing the digit conductors, a control line extending from the pushbuttons to the last said means and comprising line conductors fewer in number than the digit conductors, the said means responsive to the pushing of the pushbuttons comprising means for imparting to the line conductors a separate distinctive code for each button pushed, and the said means for energizing the digit conductors further comprising means for energizing a separate digit conductor for each said distinctive code applied to the line conductors.

4. A system for unlocking a lockable door, comprising an energizable unlocker, a group of digit pushbuttons and digit conductors corresponding respectively thereto, means responsive to the pushing of any pushbutton for energizing the corresponding digit conductor, a series of code conductors, code-assigning means for connecting any code conductor to any desired digit conductor for energization thereover, a sequence device with which the code conductors are associated and to which the first code conductor is normally connected with the remaining code conductors being normally disconnected therefrom, means responsive to the energization of any code conductor preceding the last for operating the sequence device to disconnect the currently connected code conductor from the sequence device and to connect the next succeeding one thereto, means responsive to the energization of the last code conductor when connected to the sequence device for operating the sequence device to energize the said unlecker, a timing device responsive to the said energization of any said code conductor for clearing out the sequence device at the end of a predetermined interval thereafter, and reset means responsive to the energization ot' any code conductor which is currently connected to the sequence device for resetting the timing device to restart the said interval.

5. A system according to claim 4, wherein the said clearing out of the said sequence device, by the restarted timing device at the end of the said interval following the energization of the said unlocker, deenergizes the unlocker.

6. A system for unlocking a lockable door, comprising an energizable unlocker, a group of digit pushbuttons and digit conductors corresponding respectively thereto, means responsive to the pushing of any pushbutton for energizing the corresponding digit conductor, a series of code conductors, code-assigning means for connecting any code conductor to any desired digit conductor for energization thereover, a sequence device with which the code conductors are associated and to which the rst code conductor is normally connected with the remaining code conductors being normally disconnected therefrom, means responsive to the energization of any code conductor preceding the last for operating the sequence device to disconnect the currently connected code conductor from the sequence device and to connect the next succeeding one thereto, means responsive to the energization of the last code conductor when connected to the sequence device for operating the sequence device to energize the said unlocker, a timing device for establishing a predetermined interval, and means controlled by the timing device responsive to the elapse of said interval following the pushing of any said button, with no further button push intervening, for clearing out the sequence means.

7. A system for unlocking a lockable door, comprising an energizable unlocker, a group of digit conductors and means for momentarily energizing any desired one thereof while preventing the concurrent energization of any other digit conductor, a series of code conductors, codeassigning means for connecting any code conductor to any desired digit conductor for energization thereover, a sequence device with which the code conductors are associated and to which the rst code conductor is normally connected, with the remaining code conductors being normally disconnected therefrom, means responsive to the energization of any code conductor preceding the last for operating the sequence device to disconnect the currently connected code conductor from the sequence device and to connect the next succeeding one thereto, means responsive to the energization of the last code conductor when connected to the sequence device for operating the sequence device to energize the said unlocker, a guard conductor and means for energizing it concurrently with the said energization of any digit conductor, a guard relay operable over the guard conductor responsive to energization thereof, an alarm device responsive to the operation of the guard relay, and means in the said sequence device for disconnecting the guard relay from the guard conductor to restore the guard relay, subject to the energized digit conductor being the one which is currently connected to the sequence device.

8. A system for unlocking a lockable door, comprising an energizable unlocker, a group of digit conductors and means for momentarily energizing any desired one thereof while preventing the concurrent energization of any other digit conductors, a series of code conductors, code-assigning means for connecting any code conductor to any desired digit conductor for energization thereover, a sequence device with which the code conductors are associated and to which the rst code conductor is normally connected, with the remaining code conductors being normally disconnected therefrom, means responsive to the energization of any code conductor preceding the last for operating the sequence device to disconnect the currently connected code conductor from the sequence device and to connect the next succeeding one thereto, means responsive to the energization of the last code conductor when connected to the sequence device for operating the sequence device to energize the said unlocker, a guard conductor and means for energizing it concurrently with the said energization of any digit conductor, a guard relay operable over the guard conductor responsive to energization thereof, self-locking contacts operable by the guard relay to maintain the guard conductor energized as long as the guard relay is operated, an alarm device responsive to the operation of the guard relay, and means in the said sequence device for disconnecting the guard relay from the guardconductor to restore the guard relay, subject to the energized digit conductor being the one which is currently connected to the sequence device.

9. A system for unlocking a lockable door, comprising an energizable unlocker, a group of digit conductors and means for momentarily energizing any desired one thereof while preventing the concurrent energization of any other digit conductors, a series of code conductors, codeassigning means for connecting any code conductor to any desired digit conductor for energization thereover, a sequence device with which the code conductors are associated and to which the rst code conductor is normally connected, with the remaining code conductors being normally disconnected therefrom, means responsive to the energization of any code conductor preceding the last for operating the sequence device to disconnect the currently connected code conductor from the sequence device and to connect the next succeeding one thereto, means responsive to the energization of the last code conductor when connected to the sequence device for operating the sequence device to energize the said unlocker, a guard conductor and means for energizing it concurrently with the said energization of any digit conductor, a guard relay operable over the guard conductor responsive to energization thereof, self-locking contacts operable by the guard relay to maintain the guard conductor energized as long as the guard relay is operated, means in the said sequence device for disconnecting the guard relay from the guard Aconductor to restore the guard relay, subject to the energized digit conductor being the one which is currently connected to the sequence device, a slow-operating alarm device operable responsive to a relatively prolonged operation of the guard relay, and means responsive to an operation of the alarm device for precluding energization of the unlocker and for sounding an alarm.

10. A system for unlocking a' lockable door, comprising an energizable unlocker, a group of digit conductors and means for momentarily energizing any desired one thereof while preventing the concurrent energization of any other digit conductors, a series of code conductors, code-assigning means for connecting any code conductor lto any desired digit conductor for energization thereover,

a sequence device with which the code conductors are as sociated and to which the first code conductor is normally connected, with the remaining code conductors being normally disconnected therefrom, means responsive to the energization of any code conductor preceding the last for operating the sequence device to disconnect the currently connected code conductor from the sequence device and to connect the next succeeding one thereto, means responsive to the energization of the last code conductor when connected to the sequence device for operating the sequence device to energize the said unlocker, a guard conductor and means for energizing it concurrently with the said energization of any digit conductor, a guard relay operable over the gniard conductor responsive to energization thereof, selflocking contacts on the guard relay to maintain the guard conductor energized independent of its tirst said energizing means, means in the said sequence device for disconnecting the guard relay from the guard conductor to restore the guard relay, subject to the energized digit conductor being the one which is currently connected to the sequence device, over the currently conneeted one of the said code conductors, a slow-operating alarm relay, contacts on the guard relay for operating the alarm relay subject to the guard relay remaining operated longer than a given minimum interval, and alarm-sounding means controlled by the alarm relay.

References Cited in the file of this patent UNITED STATES PATENTS 1,685,329 Lynch Sept. 25, 1928 1,923,968 Chase Aug. 22, 1933 2,250,828 Foss July 29, 1941 2,424,243 Lowell July 22, 1947 2,436,809 Joel Mar. 2, 1948 2,563,127 McGoin Aug. 7, 1951 2,855,588 Allen Oct. 7, 1958 FOREIGN PATENTS 197,503 Great Britain May 17, 1923 OTHER REFERENCES Radio and Television News, April 1955, pp. 52, 53, 158, 159, L. Garner, Jr.

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