GB2055951A - Locks - Google Patents

Abstract

A barrel lock includes an additional tumbler 30 retractable by a solenoid 35 energised by a control unit 60 controlled by sensor-contacts 40 cooperating with contacts (52) on the back of an inserted key 16. In addition to a characteristic notched profile 17 the correct key 16 has a characteristic arrangement of interconnected electrical contacts and insulating areas. Key insertion is detected by a microswitch sensor 39 and activates a delayed alarm 64 unless correct data is received. The data signal may be evaluated by comparison with a datum reference contained in a "memory" section, and in a development may also comprise a sequential signal pattern derived from tumbler actuated sensors during key insertion so as to be indicative of the notched profile. <IMAGE>

Description

SPECIFICATION Key operated locks and security systems incorporating same The present invention relates to key-operated locks, especially cylinder locks, and to security systems incorporating such locks.

Key-operated locks such as cylinder locks where operation is dependent solely upon use of a correct key having a particular predetermined notched profile are well known and widely used.

Thus, in conventional cylinder locks wherein a locking bolt is arranged to be actuated by turning of a cylindrical plug within a lock body by means of an operating key, a set of tumblers in the form of spring loaded segmented pins or spring loaded discs, slidably fitted in a series of registering radial holes in the plug and in the lock body, normally prevent rotation of the plug. When the operating key is inserted in the keyway which is formed in the plug a notched edge of the key engages and displaces the tumblers and provided the notched edge has the correct profile each tumbler is moved by an amount which is just sufficient to bring the division between pin segments or one end of the disc of the tumbler flush with the peripheral surface of the cylinder plug whereby the latter is then free to be turned.Release of the plug for turning by movement of the tumbler elements in order to operate the lock is hence a wholly mechanical function effected by the correct notched profile of the key.

Although such locks are satisfactory to a certain extent they are often not as versatile and do not provide as high a degree of security as is often desirable. Moreover they are particularly subject to the disadvantage that the keys can too readily be copied or counterfeited for complete safety.

An object of the present invention is to provide an improved key-operated lock and security system capable of affording a high degree of security and versatility and which can also be designed so that operation does not depend solely upon use of a key with the correct notched profile.

More specifically, a security system incorporating a key-operated lock of which the lock mechanism comprises a lock body housing a rotatably mounted key-engaging plug for actuating a locking bolt and includes a plurality of tumblers or locking elements arranged to lock and prevent turning of the plug unless there is inserted in a keyway of said plug the correct operating key which has distinctive predetermined physical identification characteristics including a particular predetermined notched profile, is characterised in that:: (a) at least one of the tumblers or locking elements, herein termed a safety tumbler or locking element, is operatively associated with electrically controlled retractor means and is so arranged that it remains effective to lock and prevent turning of the plug even when a key of correct notched profile is inserted unless it also is retracted into an inoperative position by operation of said retractor means; and (b) electrical control circuitry is provided in association with detector means arranged to sense insertion of a key in said keyway and also to sense whether such inserted key has at least certain of said predetermined physical identification characteristics distinctive of the correct operating key whereby to produce in response to insertion of the correct operating key an electrical output effective to cause operation of said retractor means so as to retract the or each safety tumbler or locking element and thereby to free the plug for turning by the key and normal opening of the lock.

In preferred embodiments of the invention, the distinctive predetermined physical identification characteristics of the correct operating key include, in addition to said particular predetermined notched profile, an essential further particular physical identification or coding feature which the detector means and associated electrical circuitry are arranged to sense and which must be so sensed, when a key is inserted, in order to satisfy a specific prerequisite condition for production of said electrical output effective to cause operation of the retractor means.

It may also be arranged so that if, when a key is inserted, the detector means and associated electrical control circuitry fail to sense the predetermined physical identification characteristics distinctive of the correct operating key required for producing the electrical output for operating the retractor means an alarm or warning device, possibly in association with a time delay device, is then automatically activated.

The or each safety tumbler or locking element is conveniently in the form of a pin slidably fitted in registering radial holes in the plug and lock body, the pin being either in one piece or being divided into segments of such length that a portion thereof bridges between the plug and lock body when the correct operating key is inserted until the retractor means is operated. In practical embodiments, the retractor means may comprise an electromagnetic device such as, for example, a solenoid of which the armature is formed by or is connected to a portion of the associated safety tumbler or locking element.

In some embodiments, the above mentioned essential further particular physical identification or coding feature characterising the correct operating key is provided by a particular pattern or arrangement and interrelationship of separate electrically insulating and conductive regions or areas along the shank of the key which, when the key is inserted in the keyway, co-operate with sensors of the detector means provided by a matching arrangement of electrical contacts positioned along said keyway so that portions of the electrical circuitry associated with the detector means are connected in a predetermined manner of which the pattern or arrangement represents or defines the specific prerequisite condition necessary for production of the correct electrical output required for operation of the retractor means.Alternatively, in other embodiments such essential further particular physical identification or coding feature may be provided by a specific, possibly unique, dimensional characteristic or characteristics of the key.

Also, in some embodiments the key characteristics sensed may be utilised to provide a data signal which is compared and checked against a reference standard which may be introduced or stored in a memory section of the control circuitry.

Further features will become apparent from the following more detailed description.

In the accompanying drawings, Figure 1 shows schematically, and by way of example of an embodiment of the invention, one form of key-operated cylinder lock incorporated in a security system such as may be provided for a motor vehicle; Figure 2 is an enlarged fragmentary view showing a detail of the operating key for the embodiment of Figure 1; and Figure 3 shows schematically a further embodiment of the invention in which another form of key-operated cylinder lock is incorporated in a security system which again is such as may be provided for a motor vehicle.

Referring to the drawings, the structure of the lock mechanism illustrated in Figure 1 is similar to that of a conventional cylinder lock in that it includes a lock body 10 housing a rotatably mounted cylindrical plug 12 formed with a keyway slot 14 for receiving the shank 15 of a key 16 to enable the plug to be turned to actuate a locking bolt (not shown), and a set of axially spaced pin tumblers or locking elements is provided which, until an operating key with the correct notched profile is inserted, lock the plug 12 against rotation.

In this example, three of the pin tumblers or locking elements 1 8, 1 9 and 20, corresponci to those of a conventional cylinder lock of this general type, each comprising separate radially inner and radially outer segments 18a. 186, 19a.

1 9h, 20a, 20b, slidably fitted in registering radial holes 11 a, 22b, 23a, 23b, 24a, 24b, in the plug and lock body respectively, the holes in the latter being closed at their upper or outer ends and containing bias springs 26 whereby, before insertion of the correct operating key, the tumbler pins are pressed radially inwards such that the outer segments 18b,19b,20b, bridge between the lock body and the plug thereby preventing turning of the latter. When a key with the correct notched upper edge profile is inserted, these tumbler pins 18, 19 and 20 are each moved radially outwards to an extent which is just sufficient to bring the division between the inner and outer segments flush with the peripheral surface of the plug 1 2, as indicated in Figure 1, so.

that these particular tumbler pins then no longer exercise a locking function.

The axially outermost and innermost pin tumblers 28 and 30 slidably fitted in registering radial holes 32a, 32b, and 33a, 33b respectively in the plug and lock body are, however, somewhat different. Thus, it will be seen that the tumbler 30, constituting a safety tumbler or locking element, comprises two pin segments 30a and 30b of which the radially inner segment 30a has a length that is insufficient to move the outer segment 30b clear of the hole 33a in the plug 12 when the operating key 1 6 is fully inserted, and the outer segment 30b has a relatively long length such that its upper end (as viewed in Figure 1) passes through an open upper end of the hole 33b and a projecting extension portion 30b forms or is connected to the armature of a solenoid 35.When energised, the solenoid 35 acts to complete retraction of the pin segment 30b clear of the plug 12 to permit turning of the latter, but the notched profile of the key shank 1 5 alone is ineffective in freeing the plug.

The tumbler 28 has inner and outer segments 28a, 28b, slidably fitted in the registering radial holes 32a, 32b, in the plug and body respectively, and when the key 1 6 is inserted it is moved radially outwards to an extent just sufficient to bring the division between the inner and outer segments flush with the peripheral surface of the plug so that it then no longer exercises a locking function as with the tumblers 1 8, 1 9 and 20. But, the tumbler 28 differs from the latter in that it is designed to form part of an arrangement for detecting insertion of a key and the outer segment 28b has a relatively long length such that the upper end thereof passes through an open upper end of the hole 32b, as with the pin tumbler 30b, and lies in actuating relationship with a microswitch 39.

As part of an arrangement for detecting and sensing use of the correct operating key and for controlling retraction of the safety tumbler, on the underside, as seen in Figure 1, the lock body 10 is fitted with a set of spring loaded electrical contact elements 40, five in this embodiment, mounted in a housing 42. These contact elements 40 pass through a series of holes 44 axially spaced along the length of the body 10 and extend into the keyway slot 14 which opens through the peripheral surface of the plug 12 so as to engage the lower edge face 46 of the key 1 6 when the shank portion 1 5 is inserted into the keyway.

As shown more clearly in Figure 2, the lower edge face 46 of the key is formed by a strip 50 of electrically insulating plastics material fitted and bonded into a slot or recess cut into the main metallic body part of the shank portion 1 5, but set into the insulating strip 50 are a series of electrically conductive areas provided by metal contact elements distributed in a particular pattern or arrangement characteristic of the key.

For the purpose of illustration in this example, a very simple arrangement of four such metal contact elements 52a, 52b, 52c and 52d is shown which is matched to the arrangement of the sensors provided by sensing contact elements 40.

Thus, the contact element 52a is positioned and dimensioned such that when the key is fitted in the keyway, it engages and bridges between the two axially innermost contact elements 40, while the contact element 52b engages the middle contact element 40 and the contact elements 52c and 52d respectively engage the two outermost contact elements 40 so that the electrical continuity is established between the latter since contact elements 52c and 52d are themselves interconnected through electrical leads 54 within the insulating strip 50. In this instance, contact element 52b is connected by a further lead 55 to the metal body of the key through which it is earthed via the lock body 10.

The sensing contact elements 40 are shown schematically in Figure 1 as being connected by leads C1, C2, C3, C4, and C5 to a control unit 60 of the associated electrical circuitry, this control unit 60 being designed to respond to the particular pattern or arrangement of electrical circuit continuities established by the co-operative engagement of the sensing contact elements 40 with the key contact elements 52a, 52b, 52c and 52d when the correct operating key 16 is fitted into the lock and thereby to set the lock in a condition which permits a normal opening operating upon turning the key.

Thus, in this example it may be arranged so that when electrical continuity is established between leads C4 and C5 through key contact element 52a and when lead C3 is connected to earth through key contact element 52b, a transistor controlled gate circuit is triggered and through an amplifier produces an electrical output which, via lead c6, energises a relay 62 to close a relay switch S1 and thereby causes the solenoid 35 to be energised so as to retract the pin tumbler segment 30b clear of the plug 12 thus releasing the latter for turning by the key 16.

The particular security system illustrated in Figure 1 also provides for activation of a warning device or alarm 64 if an incorrect key is inserted, for which purpose the pin tumbler 28 and microswitch 39 are utilised. During insertion of a key into the keyway 14, either the correct operating key or an incorrect key, the apex portions or high points of the notched edge 1 7 will move the pin tumbler 28 sufficiently to cause the upper or outer segment 28b to actuate the micro-switch 39 thereby to trigger a timer switch 66 which operates, after a predetermined time delay period, to complete a circuit for energising the warning device or alarm 64.The circuit to the warning device or alarm is, however, also subject to control by the control unit 60 which is arranged so that when the correct operating key 1 6 is inserted, thereby in this embodiment establishing electrical continuity for example between leads C1 and c2 through interconnected key contact elements 52c and 52d independently of the other contact elements 52, alarm control means such as normally-closed relay switch contacts in the unit 60 are actuated to open the circuit to the warning device or alarm which is thereby kept inactivated and prevented from operating.On the other hand, no such inactivation of the warning device or alarm circuit will take place if, after detecting insertion of a key, the control unit fails to sense the proper predetermined pattern or arrangement of electrical interconnections, here represented by electrical continuity between leads C1 and c2, as when an incorrect key is used.

Assuming the system depicted in Figure 1 is installed in a motor vehicle, the lock will generally be fitted as a body lock such as a door lock, while the warning device or alarm may be the usual existing horn and/or flashing hazard warning lights of the vehicle. Also, the system may readily be integrated in various ways with additional or external circuits for immobilising or controlling other functional elements of the vehicle, for example the ignition system. Thus, in one practical arrangement as indicated in Figure 1, the solenoid 35 may be associated with a normally open relay switch S2 which, through lead Ca, controls electrical continuity in the ignition circuit, the switch S2 being closed to enable the ignition to function only when the solenoid 35 is energised.

In some cases the lock may be fitted as a combination ignition switch/steering lock.

It will, however, be appreciated that similar security systems incorporating key-operated locks in accordance with the invention have a wide range of application not only in connection with motor vehicles but also in the domestic field and in the industrial and commercial fields, both in relation to the security of premises and of property and generally wherever key-operated locks are appropriate. It may even be applied to padlocks and the like since by making use of integrated circuits and developments in microelectronics and miniaturisation of electrical components to the electrical circuitry can be very compact.

Also it will be appreciated that the details of the security system and lock hereinabove described may take various forms and many modifications are possible within the scope of the invention.

For example, in the system depicted in Figure 1 as has already been indicated, the particular predetermined pattern or arrangement of electrical interconnections established between portions of the electrical circuitry by the various sensing switches (40 and 39) when the correct operating key is inserted may provide particular circuit continuities effective directly to control production of the electrical output for operating the retractor solenoid 35 and to control also activation and deactivation of the alarm 64. As an alternative, however, the system can also readily be designed so that the pattern or arrangement of electrical interconnections established by the various sensing switches and the resultant particular circuit continuities provided thereby produce, or control production of, in effect an equivalent data signal characteristic of the key which is compared and checked for matching correspondence or parity with a reference signal or quantity representing a predetermined reference pattern or arrangement characteristic of the correct operating key. Then, if correspondence or parity is found the circuitry of the control unit responds to produce the required electrical output for operating (e.g. via relay 62) the retractor solenoid 35, and to inactivate the circuit of the alarm 64.On the other hand, if there is no correspondence or parity sensed indicating an incorrect key, no output for operating the retractor solenoid will be produced and the alarm 64 will be activated.

Conventional electronic techniques and circuitry can be used for bringing about these results and the reference signal or quantity, or information or data determining the latter, can be introduced or stored, preferably in digital form, in a "memory" section of the electrical circuitry of a processing part of the control unit, and provision may be made for altering or amending and updating such reference material if, for instance, it is desired to change the correct operating key and replace it by another giving a different pattern or arrangement of electrical connections.

In the arrangements described above, the data signal referred to, which assists in identifying an inserted key and in controlling release of the lock, may be derived from and represent the particular pattern or arrangement of electrical interconnections established by the various sensing switches after completing full insertion of a key or may be derived from and represent the changes in such patterns or arrangements of electrical interconnections during the operation of inserting a key in the keyway. In the latter case, it will be appreciated that there will be a sequence of particular interconnection patterns and corresponding signals from the sensing switches which build up for example as a succession of pulses also in a particular pattern, the characteristic data signal.

With regard to the key 1 6 which has been described, the number, dimensions, arrangement, positioning and interconnections of the key contact elements (52), which represent a characteristic identification or coding feature thereof additional to the particular correct notched profile, may obviously be subject to many variations with corresponding variations as necessary in the number and arrangement of the sensors provided by the sensing contact elements 40 of the detector means and in the arrangement of the associated circuitry. In some cases, the key contact elements may be in the form of metal studs, with or without interconnecting wires, moulded into the carrier insulating material, or they may be provided by areas of metal foil on an insulating base conveniently produced, together with any interconnections required, by a printed circuit technique.Also, the insulating strip may, if desired, be provided by a plurality of separate strip segments and may have various cross-sectional configurations to suit corresponding different forms or shapes of slots or recesses cut out in the body of the key shank. Moreover, the edge face presenting the exposed contact elements can be grooved or recessed, with a V-shaped or concave cross-section for example, if required so as to facilitate effective cooperative engagement with the sensing contact elements 40 carried by the lock body.

Furthermore, the key contact elements could alternatively be positioned along other faces of the shank portion with the position of the sensing contact elements being modified accordingly. It is also possible for the body of the key to be composed principally or wholly of an electrical insulating material into which the required key contact elements are embedded. If desired, it is in fact also possible for the key to be designed to house a power supply or bias source for the electrical circuitry, in the form for example of a miniature cadmium cell perhaps in conjunction with a reservoir capacitor connected to the respective contact elements, thus providing a further distinctive characteristic.

It will also be understood that in addition to or as an alternative to identifying or coding the correct operating key by means of a particular pattern or arrangement of contact elements suitable for detection and sensing by electrical detector means associated with the lock as described, other identification or coding means which can be unrelated to or not merely dependent on the notched profile of the key may be used.Examples of these include the provision of particular predetermined electrical resistance values of circuit paths within the key established through key contact elements as described, which resistance values can be measured by the detector means and associated circuitry, and the provision of a particular arrangement or pattern of magnetic regions or inserts in the key shank which again can interact and activate suitable detector means in accordance with known technology.

Different forms and arrangements of the safety tumbler retractor means can also be used, but in general a solenoid or similar electromagnetic device acting directly or indirectly on the or each safety tumbler is most convenient and, if desired, the armature thereof may be permanently magnetised so that the device is polarised for operation by current of a particular polarity.

A lock such as has been hereinabove described is especially advantageous for improving security since the operation thereof is not dependent upon having a key merely of a correct profile, and the correct key embodying the additional identification or coding factors cannot be copied or duplicated so readily. Also, the key and external form of the lock may be such that on casual inspection it is not readily apparent that they differ from a standard conventional key and lock. And, as already indicated, such locks are well suited for development in relatively sophisticated security systems.

The mechanisms of the locks are also capable of being manufactured economically, in many cases only relatively minor modifications being needed in the techniques of manufacturing conventional cylinder locks, or existing conventional cylinder locks may be modified to suit. For example the lock shown in Figure 1 could quite easily be produced by modification of an existing conventional five tumbler cylinder lock by removing the cylindrical plug, discarding the springs of the first and fifth tumblers, drilling through the closed ends of the holes for the latter in the lock body, fitting the modified tumbler pin sections 30a, 30b and 28b, fitting the microswitch 39 and solenoid 35 to the lock body, and likewise fitting the housing with the sensing contact elements 40.Usually, in conventional cylinder locks the holes 44 in the body which accommodate the contact elements 40 will already be present for assembly purposes, and also the slot of the keyway 14 in the plug 1 2 will already intersect and open through the peripheral surface of the plug. If, however, the keyway slot is not so open, it may be enlarged so that it does not open through the surface and a key is then used which will have a shank portion of correspondingly increased depth. It will also be appreciated that instead of the safety tumbler 30 being made up of the two sections 30a and 30b, it could alternatively consist of a single long pin so long as the solenoid 35 is able to provide the greater range of movment needed for retraction of such one-piece pin into the lock body.

In a further modification or development, the lock may be arranged to function also as a key reader in respect of the notched profile of the shank. This may be achieved, for example, in relation to the embodiment of Figure 1 by arranging for the micro-switch 39 to operate when the portion of the notched edge engaged by the tumbler pin segment 28a is at a level intermediate that of the highest and iowest profiles of the notches so that during insertion of the key there will be a sequence of pulses produced having a pattern related to the particular overall notched profile and providing a data signal which may be compared and checked against a reference quantity representing a predetermined reference pattern characteristic of the correct operating key.Again such reference quantity may be entered or stored in a "memory" section of the control circuitry and it may be arranged for a matching correspondence of the data signal with such reference pattern to be a prerequisite for production of the electrical output for operating the solenoid 35, thereby introducing an additional check for use of the correct operating key.

The sensitivity and resolution of the above key profile reading arrangement may be improved by using for the micro-switch 39 a three-position switch, with three connection leads, arranged to sense and distinguish between high and low profiles of the notched edge of the key, above and below a reference level which may correspond to that of the correct depth of notch which releases the locking function of tumbler pin 28. Also, the other tumbler pins 1 8, 19, and 20, may be modified similarly after removing the springs 26 and drilling through the closed ends of the bores in the lock body, so as to co-act with additional like micro-switches whereby the profile of the key notches can be sensed giving a multi-sensing output pattern of sequential pulses containing more "bits" of information for the data signal.The latter, as produced by the correct operating key, may again be equated with a reference quantity entered or stored in a memory, and coding is also possible in the form of a combination number which, in some arrangement, might usefully be presented when required in a visual display utilising light-emitting diode (LED) display devices for example.

The embodiment shown in Figure 3 illustrates a further way in which the invention may be carried out in relation to a disc-type tumbler lock of the kind commonly used in motor vehicles. In this case, the lock includes a body 10' housing a rotatable plug 12' having a keyway 14' for receiving the shank 15' of operating key 16' and a set of spring-loaded disc tumblers 70 which normally project radially into one or other of two diametrically opposed axial slots 71a, 71b, in the body so as to lock the plug mechanically against turning but which are all retracted so that their ends lie flush with the surface of the plug when the operating key 16' having the correct notched profile along its shank is inserted.A spring-loaded pin 1 30 retractable out of locking engagement with a hole 73 in the plug 12' by a solenoid 35' connected thereto by a flexible cable 75 provides an additional safety tumbler or locking element in accordance with the invention, and detector means for detecting insertion of a key and for sensing the characteristics thereof are provided by a set of sensing switches 77, each arranged in operative relationship with a respective one of a selected group of the disc tumblers 70, and by a sensing switch 79 located at the inner end of the keyway 14'.

The sensing switches 77 in conjunction with the associated electrical control circuitry, including control unit 60', not only detect the insertion of a key but also function as a key reader in respect of the notched profile by the sequence of pulses and signal pattern, making up a data signal, produced during the operation of inserting the key in a manner similar to that already outlined in relation to the first embodiment. The sensing switches 77 may be arranged at both sides of the keyway as the tumbler discs may project either way during the key insertion operation, but there need not be a switch or pair of switches for each tumbler. For example, as shown where are a total of ten disc tumblers, it is quite satisfactory to provide six sensing switches 77 co-operating with a selected group of six tumblers at one side, and two or more at the other side, this number of sensing switches providing a large number of different combinations of individual signal sequences for making up the complete data signal depending on the particular selection of tumblers employed.

Again the sensing switches 77 are connected to the circuitry in the control unit 60' where the data signal derived from their operation while the key is being inserted may be compared and checked against a reference signal pattern, characteristic of the correct operating key, introduced or stored in a "memory" section as previously described. If matching correspondence is then established, indicating that a key is inserted which has at least the correct notched profile, and if the contacts of sensing switch 79 are also closed, an electrical output is produced which, through lead c6, energises the solenoid 35' thereby to retract the locking pin 140 and free the lock.

It will be appreciated that operation of sensing switch 79 is dependent on the effective length of the key shank 15', between the free end or tip 81 and the shoulder 83 which limits the depth of insertion into the keyway. This length dimension and the acceptable manufacturing tolerance range thereof is presently standardised for equivalent conventional notched profile keys of the same general type which are currently manufactured, at least in the United Kingdom, but in the present embodiment of the invention the key 1 6' has a non-standard shank length, for example 0.25 mm longer than that of the nearest standard length, and the sensing switch 79 is arranged so that it is just engaged and actuated by a key of this nonstandard length but it is not engaged and actuated by a corresponding standard length key even allowing for a normal manufacturing tolerance range of the latter The difference in length will not be readily apparent on casual inspection but is sufficient to distinguish the correct operating key from an incorrect key, the special non-standard length of the former again representing a distinctive particular physical identification or coding feature which is essential in addition to the correct particular predetermined notched profile.

Operation of the swtich 79 and closing of its contacts in this embodiment is thus again a prerequisite for production of the electrical output to operate solenoid 35' and, in effect, for production of the correct complete data signal derived from all the sensors. In practice, however, operation of the switch 79 may be arranged to influence the response of the control circuitry in various ways, as for example by establishing a circuit continuity which is essential for giving access to the reference data in the "memory" section or otherwise controlling the operation of establishing matching correspondence.

As before, it may also be arranged so that if no matching correspondence is established for whatever reason when a key is inserted, representing a failure to sense the correct data signal and indicating insertion of an incorrect key, an alarm or warning device (not shown) may be automatically activated. Also, the control unit 60' may be common to the sensors of a plurality of locks which have to be opened in sequence, arranged so that each has to provide the correct response signals before the next can be freed, and many other variations and developments of the basic system are possible.

Claims (14)

1. A security system incorporating a keyoperated lock of which the lock mechanism comprises a lock body housing a rotatably mounted key engaging plug for actuating a locking bolt and includes a plurality of tumblers or locking elements arranged to lock and prevent turning of the plug unless there is inserted in a keyway of said plug the correct operating key which has distinctive predetermined physical identification characteristics including a particular predetermined notched profile, characterised in that:: (a) at least one of the tumblers or locking elements, herein termed a safety tumbler or locking element, is operatively associated with electrically controlled retractor means and is so arranged that it remains effective to lock and prevent turning of the plug even when a key of correct notched profile is inserted unless it also is retracted into an inoperative position by operation of said retractor means; and (b) electrical control circuitry is provided in association with detector means arranged to sense insertion of a key in said keyway and also to sense whether such inserted key has at least certain of said predetermined physical identification characteristics distinctive of the correct operating key whereby to produce in response to insertion of the correct operating key an electrical output effective to cause operation of said retractor means so as to retract the or each safety tumbler or locking element and thereby to free the plug for turning by the key and normal opening of the lock.

2. A security system as claimed in Claim 1, wherein an alarm or warning device is also provided which is arranged automatically to be activated whenever said detector means and associated electrical control circuitry sense the insertion of a key in said keyway but fail to sense that such inserted key has the said predetermined physical identification characteristics distinctive of the correct operating key required for producing the electrical output which causes operation of the retractor means.

3. A security system as claimed in Claim 2, wherein activation of the alarm or warning device is controlled by a time delay switch device arranged to be triggered into an operative condition in response to said sensing of the insertion of a key and is controlled also by alarm control means arranged to be actuated so as to prevent activation of the alarm or warning device in response to the detector means and associated electrical control circuitry sensing that the inserted key does have such said predetermined physical identification characteristics distinctive of the correct operating key.

4. A security system as claimed in any of the preceding claims wherein the retractor means comprises an electromagnet or solenoid having a movable armature operatively connected with the or each safety tumbler or locking element.

5. A security system as claimed in any of the preceding claims associated with an additional or external electrical circuit controlled by auxiliary switch means arranged to be actuated in response to operation of said retractor means.

6. A security system as claimed in any of the preceding claims wherein the detector means comprises an electrical switch sensor connected in said electrical control circuitry and arranged to be operated by movement of a said tumbler or locking element during insertion of a key in the keyway.

7. A security system as claimed in any of Claims 1 to 5, wherein the detector means comprises a plurality of electrical switch sensors each connected in the electrical control circuitry and each arranged in operative relationship with a respective one of said tumblers or locking elements so as to be operated by movement of the latter during insertion of a key in the keyway.

8. A security system as claimed in Claim 6 or 7, wherein the operation of one or more switch sensors during insertion of the key proceeds sequentially and provides, in addition of signalling that a key is being inserted, a distinctive pattern of sequential signals related to the particular profile of the key, and wherein said electrical circuitry associated with the detector means is adapted to compare said signal pattern with a predetermined reference pattern and to check that there is a matching correspondence which forms a prerequisite for production of said electrical output effective to cause operation of the retractor means.

9. A security system as claimed in Claim 8, wherein said sequential pattern of signals provided is derived from a selected number and arrangement of said switch sensors which are operatively associated with a particular group of the tumblers or locking elements.

10. A security system as claimed in Claim 8 or 9, wherein said predetermined reference pattern is stored in a "memory" section of the electrical circuitry and can be altered to suit a change of operating key or a different selection of said switch sensors.

11. A security system as claimed in any of the preceding claims wherein the distinctive predetermined physical identification characteristics of the correct operating key include, in addition to said particular predetermined notched profile, an essential further particular physical identification or coding feature which the detector means and associated electrical circuitry are arranged to sense and which must be so sensed, when a key is inserted, in order to satisfy a specific prerequisite condition for production of said electrical output effective to cause operation of the retractor means.

12. A security system as claimed in Claim 11, wherein said essential further particular identification or coding feature is provided by a particular pattern or arrangement and interrelationship of separate electrically insulating and conductive regions or areas along the shank of the key which, when the key is inserted in the keyway, co-operate with sensors of the detector means provided by a matching arrangement of electrical contacts positioned along said keyway so that portions of said electrical control circuitry associated with the detector means are electrically inter-connected in a particular predetermined pattern or arrangement representing or defining said specific prerequisite condition for production of said electrical output required for operation of the retractor means.

13. A security system as claimed in Claim 12, wherein said particular predetermined pattern or arrangement of connections corresponds to a particular reference pattern or arrangement predetermined by reference information or data contained in a "memory" section of the electrical circuitry which can be changed or amended thereby to enable the correct operating key to be replaced when desired by another having a different characteristic pattern or arrangement and interrelationship of separate electrically insulating and conductive regions or areas which co-operate with the detector sensors to connect said portions of the electrical control circuitry in a different pattern or arrangement corresponding to the new changed or amended reference pattern or arrangement.

14. A security system as claimed in Claim 11, wherein said essential further particular physical identification or coding features of the correct operating key is provided by a particular predetermined minimum length dimension of the key shank which is such that when the key is fully inserted in the keyway the free end or tip of the shank engages and actuates an electrical switch sensor of the detector means located and arranged at the inner end of said keyway such as to sense that the key has said particular predetermined minimum length dimension, actuation of said length-sensing switch sensor representing or defining said specific prerequisite condition for production of said electrical output required for operation of the retractor means.

1 5. A security system as claimed in Claim 14, wherein said particular predetermined minimum length dimension of the key shank exceeds and lies outside any dimensional tolerance range of any pre-existing standardised corresponding length dimension of any equivalent conventional notched profile key of the same general type whereby any such latter key, if inserted into the keyway, would fail to engage and actuate said length-sensing switch sensor.

1 6. A security system incorporating a keyoperated lock arranged and constructed substantially as herein described and illustrated with reference to Figures 1 and 2 or Figure 3 of the accompanying drawings.

1 7. A security system as claimed in any of the preceding claims further characterised in that it is installed in a motor vehicle with the key-operated lock being either a body lock or a combination ignition switch/steering lock.