Improved connection of security alarm components

This invention relates to an improved connection of security alarm components.

Alarm systems have a number of components, many of which are formed from interconnected parts. An example of this is an alarm sounder

(usually referred to "a bell box") which can be mounted externally of a building or area to be protected and which is arranged to provide an audible and/or visible alarm when an alarm condition is detected by the alarm system.

Conventional bell boxes usually consist of a pair of complementary moulded plastics parts which are releasably connected together along respective edges thereof and are secured together by a screw or other fastener. Other components of the alarm system are also formed in the same way.

Most alarm components include a so-called tamper mechanism which is arranged to cause an alarm if an attempt is made to separate the interconnected parts to gain access to the interior of the components.

Due to the manner in which the component parts of alarm system components are connected together, it can be difficult to ensure that the component parts can be connected in a simple, but effective manner. Of course, if the parts are not connected correctly, it may be possible for a third party to interfere with internal components or devices without triggering the tamper mechanism. Furthermore, it may be possible to alter the operation of the component such that it does not operate when an alarm condition is detected. This is clearly undesirable.

The present invention seeks to overcome the above mentioned problem by ensuring that the components of alarm systems can be locked together in a particularly simple manner. Furthermore, it is also an object of the present invention to enable the component parts to be held together more securely than prior art arrangements thereby to provide greater security to individual alarm components and also the alarm system generally.

Thus and in accordance with a first aspect of the present invention there is provided an alarm component for use in an alarm system, said component comprising a pair of interconnected parts, said interconnected parts being connected together by cooperation of respective locking members at the edges thereof and secured by a fastening member to form an assembled said alarm component, wherein, the fastening member is moveable between positions to which the parts can be separated and in which the parts are held securely together, the fastening member being retained captive within the structure of the alarm component.

With this arrangement, it is possible to enable the parts to be connected together more easily and more securely to enhance the security of the alarm component against tampering and minimise the vulnerability of the component to being prised apart to gain unauthorised access to the interior parts of the component.

Preferably, the pair of interconnected parts of the component are arranged to connect together by a sliding motion which facilitates engagement of the interengageable formations in the respective parts. In this case, a least a part of the sliding motion may be achieved by operation of the fastener.

As an alternative, any other suitable means of attachment can be utilised which facilitates engagement of the interengageable formations on the respective parts. For example, an attachment means can be in the form of a mechanism which combines rotary and sliding movements such as that in a "bayonet" type fitting.

Preferably the fastener comprises a screw like fastener which is retained captive in a mounting on one of the component parts. The captive fastener may be constrained against movement substantially longitudinally of the mounting. The captive fastener is free to rotate about a longitudinal axis of the mounting.

Most preferably, the fastener is a screw fastener. The invention will now be described further by way of example only and with reference to the accompanying drawings, in which;

Fig. 1 shows a perspective view of one embodiment of alarm component, by way of example an alarm sounder, according to the present invention with the cover part removed for clarity; Fig. 2 shows a similar view to Fig. 1 of the cover part of the embodiment of Fig. 1 ; and Fig. 3 is a diagrammatic view, from above, of a part of the alarm component of Figs. 1 and 2.

Referring now to the drawings, there is shown in Fig. 1 , a base part 10 of one embodiment of an alarm component in accordance with the present invention. By way of example only, the invention is described as applied to an

alarm sounder or bell box. It will, however, be appreciated that the invention can be applied to any alarm or other component formed from interconnected parts.

The base part 10 is formed from a moulded plastics material but may, of course, be formed from any other appropriate or desirable material as required.

The base part 10 is formed with various features, which are not part of the present invention but these are moulded integrally therewith and can include for example a mounting 11 for a printed circuit board upon which control circuitry is provided and cones 12 to improve the sufficiency of the sound transmission from the assembled bell box. A conventional tamper mechanism 15 may also be provided and which is attached to the base part 10.

The base part 10 also has, preferably formed integrally therewith, a pair of base locking formations 13 one in each bottom corner of the part (relative to the orientation of the mounting of the bell box). Each base locking formation 13 is formed as a projecting generally C-shaped member. Whilst a pair of formations 13 are used in the embodiment described herein, it will be appreciated that any number can be utilised as desirable or as necessary. The base part 10 is also provided with a mounting 14 in which a fastening member 16 is held captive. The mounting 14 is, in the present embodiment, disposed substantially between the base locking formations 13 but can, of course, be disposed at any other position where the benefits of the present invention can be obtained.

The mounting 14 comprises a bore (not shown) in which the fastening member 16 (in the embodiment shown, a screw fastener) is held captive but which allows rotational movement of the fastener 16 for fastening/unfastening of the interconnected parts around the axis of the bore. Longitudinal movement of the fastener 16 along the axis of the bore is prevented thereby allowing the fastener to be held captive in the bore. The fastening member 16 extends along the bore of the mounting 14 and into engagement with a cradle device 18. The fastening member 16 engages the cradle 18 through a screw threaded bore in the cradle 18. It will be understood that such a connection allows the cradle 18 to move forwards and backwards relative to the mounting 14 as the fastener is fastened/unfastened.

As an alternative to the use of a cradle, any suitable device can be used which, under the action of the fastener can move, bend flex or otherwise adopt the necessary positions to carry out the function of the cradle 18 described herein.

The bore in the mounting 14 extends through a base, wall 19 of the base part 10 to accommodate the screw fastener head (not shown). A removable cover (not shown) can be provided and which may be removably attached to the base part 14. The cover would act to close off the visible bore when the bell box is assembled.

The use of a captive fastener makes it possible for the fastening/unfastening of the parts together to form a secure connection relatively simple through use of a single fastener as hereinbefore described.

The cradle 18 is a generally U-shaped member which has projecting wings 21 at an end of respective legs 22 thereof. In use the projecting wings 21 interact with the pair of upstanding limit posts 23 in a manner to be described hereinafter. Fig. 2 shows a cover part 24 of the bell box of Fig. 1 and which is also in accordance with the present invention.

The cover part 24 is formed in the same manner as base part 10 described above and is adapted for secure attachment to the base part 10.

The cover part 24 has a pair of cover locking formations 26 similar to, and capable of, locking engagement with the base locking formations 13. A cover latch 27 is provided which is upstanding from the cover part 24 between the cover locking formations 26. The cover locking formations 26 and the cover latch 27 are preferably formed integrally with the cover part 24.

Alternatively, if desired or if appropriate these members can be attached to the cover part 24 as separate parts.

Fig. 3 of the drawings shows the mounting 14 and interaction between the fastening member16 and the cradle 18 of the embodiment in more detail.

In use, base 10 and cover part 24 can be connected together as follows; The cover part 24 is placed over the base part 10 and complementary edges of parts are located relative to each other with the assistance of cooperating guide members 28 respectively formed on side edges of both the base and cover parts 10 and 24. With the cover part 24 overlying the base part 10, the two parts are not in exact registration. The latch 27 of the cover

part 24 will be disposed between the cradle 18 and the mounting 14 with respective legs 29 thereof, one each side of the fastener 16. Also, the base and cover locking formations 13 and 26 respectively will be adjacent to each other but not in locking engagement. With the respective parts 10 and 24 in the position described, the fastening member 16 can be fastened conveniently and allow the cradle 18 to move towards the mounting 14. The cradle 18 will thus engage the latch 27 of the cover part 24 and therefore continued fastening of the fastener 16 will cause a sliding motion of the cover part 24 relative to the base part 10. It will be appreciated that this relative movement will cause the base and cover locking formations 13 and 26 on the respective parts, to engage with each other. The engagement of the locking formations 13 and 26 acts to securely lock an edge of the bell box along which these formations are positioned, and the locking will be sufficient to prevent access to the interior of the bell box itself. Furthermore, the interior engagement between the latch 27 and the cradle 18 will assist in the security of the bell box. With the edge of the bell box secured in the simple manner indicated, it will be appreciated that the bell box is substantially more secure and less vulnerable to tampering than conventional bell boxes. It will further be recognised that the secure locking of the parts of the bell box is achieved by utilisation of a single fastener. This is how conventional prior art components are connected but with the present invention, the engagement of the locking formations 13 and 26, caused by operation of the fastener 16 provides a much greater level of security than is

present in known systems. Furthermore, since the locking of the parts together is carried out by using only a single fastener 16, as with prior art bell boxes, it will be appreciated that the much increased security provided by the present invention does not result from any great increase in the complexity of the interconnected parts or the mechanism for securing the parts together.

To open the bell box, the fastener 16 is rotated in the opposite sense to unlock the parts 10, 24. The cradle 18 is moved away from the mounting 14. Thus, the cradle 18 will once again engage the latch 27 of the cover part 24 and will push the cover part 24, in a sliding motion, away from a position of exact registration with the base part 10 to a position of inexact registration.

As mentioned above, a pair of upstanding posts 23 are provided which are attached to or formed integrally with the base part 10 and this act to limit the extent of travel of the cradle 18 relative to the mounting 14. This limiting action is achieved by engagement of the wings 21 of the cradle 18 with the post 23 to prevent further movement in that direction. The posts 13 are formed at a sufficient distance from the mounting 14 such that when the wings 21 of the cradle 18 engage the posts 23 the locking formations 13 and 26 respectively on the base and cover parts 10 and 24, are in a position where they have separated longitudinally and therefore are no longer in engagement whereby the cover part 24 can be separated from the base part 10. In fact, the positioning of the posts 23 can be chosen such that when resistance is felt to the movement of the screw fastener 16, this is an indication to the user that the relative positioning of the cover and base parts 10 and 24 is such that the cover part 24 can be lifted away, and separated from, the base part 10.

The removal of cover part 24 is assisted by guide members 28 which are shaped such that as the cover part 24 is slid to disengage the inter engageable formations on the respective parts, the cover 24 will ride up a suitably shaped top of the member 28 to allow the cover part 24 to be moved to a position where the inter engageable formations on the respective parts are spaced from each other whereby the cover part 24 can be removed.

It will of course be understood that the arrangement of the present invention leads to a substantial increase in the security of a bell box and this is achieved in a particularly simple and inexpensive manner. Furthermore, the use of a captive fastener 16 to connect the two parts 10 and 24 together enables the difficulties associated with loose fixing, such as dropping or losing the fixings, to be minimised for an installer or engineer.

Still further, the arrangement of the present invention also provides for an increase in sensitivity of a conventional tamper switch arrangement. Tamper switches are usually provided internally of the bell box and these switches activate an alarm if an attempt is made to separate the two parts of the bell box in an attempt to gain access to the interior. In conventional bell boxes such devices normally will only respond to movement in a perpendicular plane to the bell box parts i.e. the sensing is done in such a way that movement of the cover part 24 relative to the base part 10 causes the tamper switch to become activated so long as such movement is in a perpendicular direction. With the present invention, the sliding motion of the cover part 24 relative to base part 10 can be used to sense tampering by

sensing movement in a longitudinal direction as well. Therefore it will be appreciated that the sensitivity of the tamper arrangement can be increased.

It will of course to be understood that the invention is not intended to be restricted to the details of the above embodiment which is described by way of example only.

Thus, for the avoidance of doubt, whilst the embodiment described is in the form of a bell box, the invention is equally applicable to any other part of an alarm or other system which relies on the security of the interconnection between two parts.