The present invention relates to a lock mechanism, in particular to a lock mechanism having an improved strength.

The majority of lock barrels sold for use with PVC type doors (although they may be used with other types of door) are of the design known as "Euro cylinder" or "Euro profile" locks. Although these locks are used industry wide there are a number of disadvantages with them, in particular they are prone to snapping when subjected to particular loads. This weakness found in these types of locks is well known and documented. However due to the widespread use of these cylinders there has been no fundamental change in the cylinders used although some manufacturers do provide cylinders out of materials of increased strength in attempt to overcome this problem.

The problem is inherent in the design of the Euro profile cylinder. As shown in Figure 1 the Euro profile cylinder lock 2 has a "keyhole" shaped profile that has a narrow central section 4, extending below the cam 6, that holds the two halves 8, 10 together. The strength of this central section 4 is severely compromised as a fixing hole 12 passes through it. This leaves a very small "bridge" of material above and below the fixing hole that is susceptible to snapping if a strong tool is inserted into the lock and a sharp angular movement is applied. As shown in Figure 2, which depicts a snapped euro profile cylinder lock, the actual structural thickness of the lock in this section leaves only a very small area of material 14, 16 on either side of the fixing hole 12 which compromises the overall strength of the lock. Once the cylinder lock is snapped it is a simple process for an intruder to access the interior of the lock to unlock the door.

Furthermore, cylinder locks of this type are highly vulnerable to 'bumping'. Bumping is a lock picking technique whereby a modified key (typically called a bump key) is inserted part-way into the lock. The bump key has a series of small teeth usually of equal height which line up with the pins in the cylinder. The key is then struck sharply to force part of each of the cylinder pins across the shear line while leaving the remainder of each pin in place in the cylinder. As the pins return to their usual positions there may be a brief window in which no part of any pin resides across the shear line and thus the cylinder may be rotated and the door unlocked. By the term 'resides across the shear line' we mean that one end of the pin extends into the cylinder whilst the opposite end extends into the casing. Thus, when any pin resides across the shear line the cylinder cannot be rotated. In contrast, when no part of any pin resides across the shear line, for example when each pin sits wholly on one side of the shear line, the cylinder is free to rotate. Thus, the cylinder will rotate even when the ends of the pins are substantially aligned with the shear line.

EP1997982 describes a prior lock design comprising a number of locking pins which is adapted to prevent forced entry by bumping the lock.

The present invention proposes a new lock design that offers improved strength and resistance to bumping attacks. According to a first aspect of the invention there is provide a cylinder lock comprising: a top section comprising a barrel having a through passage at either end, said barrels separated by a cam opening; a lock provided at each end in the through passages; a cam member located between the locks; a middle section extending from the top section and having a width less than that of the top section, and a lower section extending from the middle section such that it bridges the cam opening; and wherein the width of the lower section is greater than the width of the middle section.

The lower section may be substantially equal to the width of the top section. This increased lower section width strengthens the resistance of the cylinder lock to being snapped as described herein above.

In a preferred embodiment the width of the middle section is 10mm or less. Alternatively the width of the middle section is in the range of 9mm to 1 1 mm, for example the width of the middle section may be 10mm.

The cam opening may extend into the middle section. Preferably the lower section extends substantially along the length of the cylinder lock. In a preferred embodiment the cylinder lock may be provided with a hole in its lower section for receiving a retaining screw therein. As the hole is provided in the lower section, which has a greater cross sectional area, the remaining material above and below the hole is increased compared to a standard euro profile cylinder, thereby increasing the resistance of the cylinder lock to snapping resulting in a lock that provides a higher level of security. The lock may comprise a cylinder lock of any variety as described above, further comprising a plurality of pin assemblies, said pin assemblies each comprising a spring and at least one pin selected from the group comprising of standard pins, extended pins, anti-pick pins and T-pins. According to a second aspect of the invention there is provided a casement lock comprising: a primary locking means moveable between secured and retracted positions in respective first and second directions; primary actuation means for selective movement of the primary locking means in the first and second directions; secondary locking means selectively operable to prevent movement of the primary locking means in the second direction; the casement lock further comprising an opening therein for receiving a cylinder lock therethrough for selectively actuating the secondary locking means; said opening comprising a top section for receiving a cylinder lock barrel therein; a middle section extending from the top section and having a width less than that of the top section, and a lower section extending from the middle section; and wherein the width of the lower section is greater than the width of the middle section.

The casement lock can receive a standard euro profile cylinder lock or can receive a high security cylinder lock according to the first aspect of the invention. In this manner an easy installation is effected as the casement lock can be fitted to, for example, a door and the security level can be dictated at point of installation of the door by fitting one of a euro-profile cylinder lock or a new high security cylinder lock as described herein. According to a third aspect of the invention there is provided a locking system for a closure, the system comprising: a casement lock comprising: a primary locking means moveable between secured and retracted positions in respective first and second directions; primary actuation means for selective movement of the primary locking means in the first and second directions; secondary locking means selectively operable to prevent movement of the primary locking means in the second direction; the casement lock further comprising an opening therein for receiving a cylinder lock therethrough for selectively actuating the secondary locking means; and a cylinder lock according to the first aspect of the invention; wherein the opening substantially conforms to the shape of the top and middle sections of the cylinder lock.

In a preferred embodiment the opening is further shaped to conform to the lower section of the cylinder lock.

The opening may define a shape that closely surrounds said cylinder lock so as to prevent rotation thereof.

In this manner a locking system can be provided which can be used with a the cylinder lock of the first aspect of the invention but which, if required by the user, may have the cylinder lock removed and replaced with a traditional euro profile cylinder, which will be understood by the skilled person to be one having the profile shown in Figure 1. In this manner, if required, the high security profile cylinder lock can be replaced with a standard cylinder lock without the need to adapt the casement lock, or vice versa

Preferably the casement lock has a hole therein, and the locking system further comprises a screw that passes through said hole and into said cylinder lock so as to retain it.

In one embodiment, the cylinder lock may comprise: a top section comprising a barrel having a through passage at either end, said barrels separated by a cam opening; a lock provided at each end in the through passages, and a cam member located between the locks; a middle section extending from the top section, and a lower section extending from the middle section such that it bridges the cam opening; and a plurality of pin assemblies, said pin assemblies each comprising a spring and at least one pin selected from the group comprising of standard pins, extended pins, anti-pick pins and T-pins.

According to a fourth aspect of the invention, any of the cylinder locks as described previously may further comprise at least one spring force adjustment means operable, in use, to increase or decrease the force exerted by said spring. The spring force adjustment means may adjust the displacement of the spring and/or the rotational torque in the spring, relative to its relaxed position. For example, the spring force adjustment means may comprise a grub screw attached to an end of the spring.

The pin assembly or assemblies may be housed within a bore or bores in the lock, said bore or bores may comprise a screw thread on an internal surface thereof for cooperating with said grub screw. In one embodiment, the spring force is adjusted by screwing or unscrewing the grub screw, thereby adjusting the length and/or torque in the spring.

In alternative embodiments, the spring force adjustment means may comprise a spacer. The spacer may be attached to or abut an end of the spring. In some embodiments, the bore or bores may be further provided with a cap to cover an external end of the bore or bores.

The spacer takes up some of the available depth in the bores. This results in compression of the spring which increases the force exerted by the spring. The increase in force exerted by the spring is dependent on the length of the spacer used.

In further embodiments, the spring force adjustment means may comprise a combination of a grub screw and a spacer. The spacer may be located between an end of the spring and the grub screw.

The spring force may be adjusted by screwing or unscrewing the grub screw. The grub screw may rotate against the spacer, which in turn increases or decreases the compression of the spring. An advantage of using the combination of the spacer with the grub screw is that the spring is prevented from being twisted as the grub screw is rotated.

In one embodiment, the cylinder lock comprises a plurality of spring force adjustment means wherein one or more of the spring force adjustment means may be operable independently of the other spring force adjustment means. According to a fifth aspect of the invention, any of the cylinder locks as described previously may further comprise at least one slot in at least one of the locks provided in the through passages of the barrels. The at least one slot may be positioned along the lock to ensure that there is at least one pin assembly in both a front portion and a rear portion of the lock.

Alternatively or in addition, at least one of the barrels further comprises at least one groove. The at least one groove may be positioned along the barrel to ensure that there is at least one pin assembly within both a front portion and a rear portion of the barrel.

The at least one slot may be linear. The at least one slot may extend partially around the circumference of the lock. The at least one slot may or may not be visible when the lock is situated in the through passages. Each lock may comprise two slots.

In some embodiments, at least one of the locks is provided with a horizontal slit across an internal end of the lock.

In some embodiments, the at least one groove may extend partially around the circumference of barrel. Each barrel may comprise one groove.

An embodiment of the invention will now be described, by way of example, with reference to the following drawings in which: Figure 1 shows a prior art euro profile cylinder lock;

Figure 2 shows a snapped prior art euro profile cylinder lock;

Figure 3 shows a new design cylinder lock in accordance with the first aspect of the invention;

Figure 4 shows a casement lock in accordance with the second aspect of the invention; Figure 5 shows the locking system of the third aspect of the invention; Figure 6 shows the casement lock of the second aspect of the invention fitted with a euro-profile cylinder lock;

Figure 7 shows a cross section of the cylinder lock of the fourth aspect of the invention;

Figure 8 shows a cross section of the cylinder lock of the fourth aspect of the invention fitted with an alternative arrangement of pins;

Figure 9 shows the cylinder lock of the fourth aspect of the invention as viewed from below.

Figure 10 shows a cylinder lock in accordance with a further embodiment of the fourth aspect of the invention; Figures 1 1A to 1 1 C show a lock in accordance with a fifth aspect of the invention; and

Figure 12 shows a side view of a cylinder lock in accordance with an embodiment of the fifth aspect of the invention. Figures 1 and 2 show a known lock of the euro profile cylinder according to the prior art and are described above.

Figure 3 shows a high security alternative non euro profile cylinder lock of the invention, which has an improved resistance to snapping compared to the euro profile cylinder lock shown in Figures 1 and 2.

The cylinder lock 102 has a top section 1 16 comprising a barrel 108 which has a through passage at either end. The barrels 108 are separated by a cam opening in which a cam 106 is located. A lock 134 is provided at each end in the through passages 108. A middle section 1 18 extends from the top section 1 16 and has a width less than that of the top section. A lower section 104 extends from the middle section 1 18 such that it bridges the cam opening. The width of the lower 104 section is greater than the width of the middle section 118. As can be seen, the thickness of the lower section 104, i.e. below the cam 106 is wider than that of the euro profile cylinder. However, between the barrel 1 16 of the lock and the lower section 104, the middle section 1 18 is narrower than both the barrel 1 16 and the lower section 104. This necked middle section 1 18 has approximately the same width, or a lesser width that a euro profile lock cylinder, i.e. the width is approximately 10mm or less.

The effect of these differences in the cylinder lock is that, at the bridge section 110, the cross sectional area of the material that must be broken to snap the lock is increased compared to that of the euro profile cylinder lock. This increased cross sectional area at the snap point increases the force necessary to snap the lock cylinder of Figure 3 thereby increasing its strength and reducing its susceptibility to destruction in the known manner. Accordingly, when used in a lock, the cylinder lock 102 of the invention will result in increased security.

Referring to Figures 4 to 6 a casement lock and locking system of the invention are shown. The casement lock differs from previous casement locks used with euro profile lock cylinders in that the shape of the opening 124 therein which receives the cylinder lock has an enlarged lower section 1 14 so that it can receive the cylinder lock of the invention. However, as the opening 124 of the casement lock has a narrower necked portion 120, when it is fitted with a standard euro profile cylinder lock, as shown in Figure 6, the euro profile lock cylinder is prevented from rotating as its lower section 122 is retained in the necked section 120 of the casement lock. The necked section 120 of the casement lock is therefore dimensioned to closely receive a euro-profile cylinder lock, i.e. it is dimensioned such that the opening is slightly larger than 10mm such that when a euro profile cylinder lock 2 with a 10mm lower section 122 is inserted it is prevented from rotation by the necked portion 120. As the casement lock 112 easily accommodates either a standard euro profile cylinder lock, or the new high security cylinder lock as described in relation to Figure 3, the locking system can quickly and easily be changed for a standard locking system to a high security locking system by changing the cylinder lock with no further adaption of the casement lock being required.

Standard euro profile cylinder locks are cheap to manufacture due to the large number of these cylinder locks that are produced and, accordingly, give a very good value solution where additional security is not required. In addition, casement locks that accept the euro profile cylinder are produced and sold in relatively high quantities, which enables their production to take advantage of the benefits of mass manufacture resulting in efficient manufacture of these products.

As the improved strength cylinder locks 102 will only be required to be used in a limited number of applications the production of these lock cylinders, and the casement locks to accept these new cylinders can not take advantage of the benefits of mass manufacture as the quantities are not great enough. The present invention proposes a solution to the problem in which a common casement lock 1 12 can accept either a standard euro profile lock cylinder or can accept the alternative improved strength cylinder lock 102 described above.

The casement lock 112 may be any form of known casement lock that accepts a cylinder lock therethrough. In the embodiment shown the casement lock has a primary locking means 126 which is moveable between a secured and retracted position in a first and second direction. As will be appreciated by a person skilled in the art, in use the casement lock 1 12 is received within a closure, for example a door, such that an edge 128 thereof is substantially flush with an edge of the closure. The primary locking means 126 interacts with some form of abutment member located in or on a frame surrounding the opening that the closure closes, for example an abutment within a door frame. The primary locking means 126 as shown in Figure 4 comprises a hook member which is rotatable about its pivot point 130 in the first and second directions to enable it to hook around the aforementioned abutment means on the closure frame. A primary actuation means 132 is provided, the movement of which moves the primary locking means between its secured and retracted positions. As shown in Figure 4 the primary actuation means 132 comprises a rotatable member. As will be appreciated by the skilled person, the member 132 is rotated by means of a square spindle which passes therethrough and attaches to a handle of the type known in the art on at least one side of the closure. A secondary locking means within the casement lock is operable to prevent movement of the primary locking means 126 in its second direction, i.e. from its secured position to its retracted position. The secondary locking means therefore prevents unlocking of the closure by preventing movement of the primary locking means. Details of the secondary locking means are not shown in Figure 4 but will be apparent to those skilled in the art and may be of any form known in the prior art. The casement lock has an opening 124 therein for receiving a cylinder lock. In use the cylinder lock selectively actuates the secondary locking means.

Referring to Figure 5 as can be seen opening 124 closely surrounds, and conforms to, the shape of the middle and lower section of the casement lock 102 of the invention The locking system of the present invention therefore provides a casement type locking system which can be used with either a euro profile cylinder lock (Figure 6) or alternatively with an alternative non-euro profile cylinder lock (Figure 5). Advantageously by providing a common casement lock that can be used with either a standard euro profile cylinder lock or with the alternative non-euro profile cylinder lock described above, the benefits of mass manufacture currently enjoyed for euro profile casement locks can be maintained whilst also providing the end user with greater flexibility as to the type of lock cylinder that they can use with that casement lock, i.e. they can quickly and simply modify the locking system by insertion or removal of either type of cylinder lock. Furthermore, by providing a casement lock which can accept different profiles of cylinder lock, if in the future the owner wishes to upgrade their standard euro profile cylinder lock to a higher security cylinder lock, this can be done without needing to change the entire door hardware thereby giving greater consumer flexibility.

Referring now to Figure 7, there is shown a cylinder lock according to a fourth aspect of the invention. The cylinder lock 200, as well as being stronger than a euro profile cylinder for the reasons previously described, also has increased resistance to 'bumping'-type attacks. Additionally, this further aspect of the invention may be applied independently of the teaching of some, any or all of the first to third aspects described above.

The cylinder lock 200 has a top section 201 comprising a barrel 202 with a through passage at either end for receiving a key 203. The cylinder is held within a housing 204 which extends to the bottom section 205 which, in the present embodiment, is strengthened according to the first aspect of the invention.

In use, the key 203 is inserted into either end of the through passage in order to actuate the barrel 202. When inserted, the key 203 depresses the series of six pin assemblies 210. The pin assemblies are housed within a bore 220, in this case a cylindrical channel, which extends from the lower face 230 of the bottom section 205 into the through passage of the barrel 202. The bore comprises two sections, an upper bore 221 which has a screw-threaded internal surface at least in part, and a lower bore 222, which has a wider diameter than the upper bore 221.

The pin assemblies 210 each comprise a first pin 212, and intermediate pin 213 and a third pin 214 to which a first end of a spring 215 is attached. At the opposite end of the spring 215 is attached a spring force adjustment means, in this case a grub screw 21 1. The grub screw 21 1 interacts with the screw-thread on the internal surface of the upper bore 221 so that the length of the spring 215 may be adjusted by either screwing or unscrewing the grub screw 211 in the upper bore 221. By adjusting the length of the spring 215 it is possible to adjust the amount of force provided by the spring 215 to the pins 212, 213, 214, since the force exerted by the spring is proportional to its displacement from its relaxed position (i.e. by compression or extension). This arrangement therefore provides a method by which the spring force acting upon one or more of the pins may be adjusted, without requiring the replacement or modification of any of the components, the advantage of which is described below. In an alternative embodiment (not shown), the spring force adjustment means is a spacer. The spacer may be provided within the upper bore and may be attached to or abut an end of the spring. The presence of the spacer results in compression of the spring and thus the amount of force provided by the spring can be adjusted. The spring force of each spring and pin can be individually varied by providing different lengths of spacer and/or by omitting the spacer for at least one spring and pin.

Figure 7 also shows 4 different varieties of intermediate pin 213 A-D. 213A is a standard pin, 213B is an extended pin, 213C is an anti-pick (spool) pin, and 213D is an extended anti-pick pin. Varying the length of the pins means that a different spring force acts upon the pins when the key is inserted. The anti-pick pins work in the conventional manner, i.e. the narrower central portion means they jam in the bores 220 at the shear line when torque is applied to the barrel 202. The wider ends of the pin prevent the pin being pushed beyond the shear line (for example by a pick) without first releasing the torque upon the barrel and thus dropping all the pins. Referring now to Figure 8 there is shown a lock 300 similar to the lock 200, and where similar parts shall not be renumbered. Lock 300 is further equipped with a T-pin 301 in a bore 220. The T-pin 301 comprises a body 303 with a wider head 302, attached to a spring 215. The T-pin acts as an anti-picking device via the same mechanism as the anti-pick pins 213C and 213D. The body 303 of the T-pin 301 is housed within the spring 215, so that the spring 215 is allowed to extend much further than the other springs in the lock. This increased extension means the energy stored in the spring, and thus the force required to act against it and move the first pin 212 is different to the remaining springs. In an alternative embodiment (not shown), the spring connected to the T-pin has a different length to the other springs used in the lock, so that the spring force is different. As with the embodiment of Figure 7, the spring force may be adjusted for this spring and pin independently of that of the other pins.

Referring now to Figure 9, there is shown the locks 200, 300 from below. The lower face 230 of the lock has a series of bores 220 extending therefrom. Accessible through the bores 220 are the grub screws 211 which are provided with a hexagonal recess 231 for receiving an Allen key (not shown). In an alternative embodiment (not shown) the grub screws have an alternative shaped recess, for example, a straight or cross shaped slot for receiving a screwdriver. An Allen key can thus be used to screw or unscrew the grub screw 211 in order to move the grub screw 211 relative to the bore 220 and alter the length of the spring 215.

The grub screws can either be attached to one end of the spring, or simply abut one end, so that the grub screw can rotate freely relative to the spring. As the grub screws position is moved within the bore, the length of the spring, and thus the displacement from its relaxed position is altered, and the force exerted by the spring changes. In an alternative embodiment (not shown), the grub screw is attached the spring so that it may not rotate relative to the spring, for example by an end of the spring being inserted through a portion of the screw, the use of adhesives or soldering, by clamping a portion of the screw or any other suitable method. Thus, when the grub screw is rotated it imparts a torque onto the spring, thereby adjusting the force required to displace the spring.

With reference to figure 10, there is shown a lock 310 which is similar to the lock 200 and lock 300. Similar parts have not been renumbered. In lock 310, the spring force adjustment means is a combination of a grub screw and a spacer. In the present embodiment, each spring and pin is provided with a grub screw and a spacer. The spacers 312 are located between the springs 215 and the grub screws 211 (not visible). In lock 200 and lock 300, when the grub screws are rotated to alter the length of the springs 215, and thus the force exerted by them, it is possible for the springs 215 to become twisted. In the present embodiment, the grub screws are attached to or abut the spacers 312. Thus, when the grub screws are rotated, they turn or turn against the spacers 312 rather than the springs 215. Therefore, when the grub screws are tightened, the spacers 312 are pushed upwards and compress the springs 215. This enables the force exerted by the springs 215 to be increased without the springs 215 becoming twisted.

The locks 200, 300 in figures 7, 8, 9 and 10 therefore have an increased resistance to bumping or picking as described below. The locks comprise 3 mechanisms for adjusting the spring length and thus the force exerted by the springs: the length of the intermediate pins 213; the T-pin 301 which is housed within the spring; and the grub screw 21 1 and/or spacer 312. The desired pins must be selected during manufacture or as part of a retrofit, however the grub screw allows the spring displacement to be adjusted in situ.

The use of grub screws therefore has a number of benefits over locks without such spring force adjustment means. Firstly a user, for example a locksmith or even an unskilled person can adjust the force exerted by the springs with conventional tools, without the lock needing to be dismantled or springs replaced. The exerted force is also much more adjustable compared to other known mechanisms, since the grub screw can be moved to any position along the length of the bore. Furthermore, the grub screws make it simple to adjust the force exerted by the springs at any point in the lock's life; a user simply removes the lock from the door and adjusts the spring displacement before reinstalling the lock. It is not necessary to disassemble the lock or purchase replacement parts. Additionally, none of the adjustments to the grub screw require any changes be made to the key.

The adjustment of the force exerted by the springs is highly desirable in a lock to mitigate the effect of bumping. Bumping a lock relies on the principle of conservation of momentum - by striking the first pin in a row, the last pin is forced away from the key while leaving the first pin unmoved. The present invention utilises a series of three pins, whereby it is the intermediate pin that sits across the shear line and prevents rotation of the barrel, so that in a bump, the movement of the last pin does not affect the lock. In locks where the springs are all the same length and/or have the same spring force, the response from the spring is likely to be common across all the pins. Thus it is relatively straightforward to bump the lock as all the pins 'jump' in similar fashion. However, with differing spring forces across the pins assemblies, the springs and thus pins react differently - it may be possible to get some pins out of the shear line but it is markedly more difficult to bump all pins simultaneously. Unless all the pins can be moved by the precise distance required and at the same time, the lock remains in the locked position and the barrel cannot rotate. Should the lock be successfully bumped, it is relatively straightforward to reset the lock by changing one or more of the spring displacements. Thus a person trying to bump the lock would need to re-learn the feel of the lock in order to successfully bump it a second time.

The combination of anti-pick pins, extended pins, T-pins and grub screws and/or spacers allow for a highly customisable lock, without requiring a new key to be cut. The above components may be included in any combination, number and order in the lock, thus making the lock's response almost impossible to predict.

The spring force adjustment means are particularly suitable for use with high security locks as described above and shown in Figure 3, since the lower section 104 is sufficiently enlarged, compared to conventional euro profile cylinders, to accommodate the extra components.

Referring now to Figures 1 1A to 11 C, there is shown a lock 400 according to a fifth aspect of the invention. The lock 400 is provided with a first linear slot 402 which extends partially around the circumference of the lock 400. A second linear slot 404 is provided diametrically opposite the first linear slot 402. The second linear slot 404 extends partially around the circumference of the lock 400. The first linear slot 402 and the second linear slot 404 are positioned so that there is at least one pin assembly in both a front portion 406 and a rear portion 408 of the lock. The front portion 406 of the lock extends from the first slot 402 and the second slot 404 to the external end 410 of the lock 400. The rear portion 408 of the lock extends from the first slot 402 and the second slot 404 to the internal end 412 of the lock 400. The first linear slot 402 and the second linear slot 404 do not extend fully across the top or bottom of the lock 400. The maximum depth of the first linear slot 402 and the second linear slot 404 is dictated by the space required to accommodate the pin assemblies and grub screws described above. A horizontal slit 414 is provided across the internal end 412 of the lock 400.

As explained above, traditional Euro cylinder locks are susceptible to snapping due to the very small bridge of material above and below the fixing hole. The cylinder locks of the present invention have increased strength and reduced susceptibility to destruction due to the increased cross-sectional area at the bridge section. Inevitably, increasing the strength of the bridge section results in a different area of the cylinder locks being the new weak point. The weakest point of the present cylinder locks is now at the barrel and if sufficient rotational force is applied by an intruder to the external end of the locks, the barrel may snap and the lock may become unsecured. In the lock 400, the first slot 402 and the second slot 404 are provided to ensure that the weakest point of the cylinder lock is between them. If sufficient rotational force is applied to the external end 410 of the lock 400, the front portion 406 of the lock 400 will be forced to rotate. However, the horizontal slit 414 across the internal end 412 of the lock 400, keeps the rear portion 408 of the lock 400 in place and substantially prevents it from being rotated within the through passage of the barrel. The lock 400 will therefore break at the first slot 402 and/or the second slot 404. Since the front portion 406 of the lock has been forcibly rotated, the pin assemblies in the front portion 406 of the lock no longer function and the front portion 406 of the lock 400 will become unsecured. However, since the rear portion 408 of the lock 400 has not been forcibly rotated, the at least one pin assembly in the rear portion 408 of the lock 400 is unaffected and functions as normal. Thus, the rear portion 408 of the lock 400 remains secured and the door cannot be opened.

Referring now to Figure 12, there is shown a lock cylinder 500 according to an embodiment of the invention. In addition to, or as an alternative to the lock 400 described above, each of the barrels 502 and 504 of lock cylinder 500 are provided with a groove. A first groove 506 extends partially around the circumference of barrel 502. A second groove 508 extends partially around the circumference of barrel 504. The first groove 506 is positioned so that there is at least one pin assembly contained within both the front portion 510 and the rear portion 512 of the barrel 502. Similarly, the second groove 508 is positioned so that there is at least one pin assembly contained within both the front portion 514 and the rear portion 516 of the barrel 504. The first groove 506 provides an area of weakness within the barrel 502. If a sufficient rotational force is applied to the external end 518 of the lock cylinder 500, the barrel 502 will break at the first groove 506. As explained above, the at least one pin assembly contained within the rear portion 512 of barrel 502, will remain in place to ensure that the rear part of the lock cylinder remains secured and the door cannot be opened. The second groove 508 is designed to secure the door in a similar manner when sufficient rotational force is applied to the end of barrel 504.