GB2099197A

GB2099197A - Intruder alarm

Info

Publication number: GB2099197A
Application number: GB8215478A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-05-27
Filing date: 1982-05-27
Publication date: 1982-12-01
Also published as: GB2099197B

Abstract

An intruder alarm has a housing (1) with a switch (4) comprising metal contacts and a metal sphere (9) located in the chamber 1. In operation the housing (1) is balanced on one end (1d) and the sphere (9) is also balanced on a metal stud (10) using a removable non-conductive key (8). A ring (14) is connected to the upper end (1a) from which a trip wire is strategically extended. If the wire is tripped or the housing knocked, the housing will be unbalanced and the sphere (9) is displaced from its balanced position completing an electrical pathway between contacts (10 or 11 and 12). An audio alarm is then actuated. In order to switch off or to reset the alarm (3) a key (8) is inserted through apertures (7a) at one end (1b) and its legs (8a) separate the sphere (9) from the metal contacts (10 or 11 and 12) thus deactivating the alarm. <IMAGE>

Description

SPECIFICATION Sonic intruder alarm The present invention relates to intruder alarms for generating an acoustic signal particularly, but not exclusively, for use in domestic, or small business, premises.

There is known a sonic intruder alarm of the type having a key attached to a cord, such that if the cord is tripped by an intruder the key is pulled from the alarm and a spring-loaded contact completes an electrical circuit activating the alarm and causing an acoustic signal to be generated. A disadvantage of this type of alarm is that the key remains in proximity to the alarm once removed and if the key is reinserted the sonic alarm signal is switched off. A further disadvantage is that reasonable force is required to be applied to the cord to produce removal of the key and an intruder proceeding cauti ously may feel the cord, and not actuate the alarm. These disadvantages limit the usefulness of this type of device.

An object of the present invention is to obviate or mitigate the abovesaid disadvantages.

According to the present invention there is pro vided an intruder alarm comprising, a housing adapted to be balanced in a position of equilibrium, said housing including acoustic signal generating means and power supply means, switch means located in said housing and adapted to be arranged such that when said housing is balanced in said equilibrium position said switch is off and when said switch is unbalanced, said switch is on permitting said power supply means to actuate the acoustic signal generator means.

Preferably said alarm means includes removable key means which is insertable into the housing, whereby when said key means is inserted, the switch means is switched off or reset.

Preferably also, said switch means comprises an electrical conducting element and two electrical contacts of different polarity, said electrical conducting element being balanced on the electrical contact when the housing is balanced the switch being off, and when said housing is unbalanced said electrical conducting element contacts each electrical contact.

Preferably also, the electrical conducting element is a sphere, and the electrical contact on which the spere is supported when the switch is off is a cylindrical stud rim in which the sphere is seated when in the balanced position.

Preferably also, said key means has a plurality of generally parallel longitudinal legs, each leg being spaced around the periphery of the key and each leg having the same or a different cross-section.

Preferably also said housing has a first end cap, the cap having a plurality of apertures located therein, each said aperture adapted to receive a respective leg of said keytherein.

Preferably also, the first electrical contact is posi tive and second electrical contact is negative.

Preferably also, the housing is electrically conductive, and being connected between said negative supply of the power supply means and said negative contact.

Preferably also, said negative contact is a ring located in the inner surface of said housing portion in which said switch means is located.

Preferably also, the other end of the housing has a removable end cap located therein, said plug having a shaped recess adapted to co-operate a shaped projection on plug extraction means.

Preferably also, the first end cap and the removable end cap of the housing are made of electrically insulating material.

Preferably also, the shape of the apertures of the first end cap and legs of the removable key means can be selected for co-operation.

Preferably also, ring means are provided at said one end of the housing for attaching a cord thereto.

Preferably also, said housing portion includes another positive electrical contact located opposite the first positive contact, the other electrical contact being shaped such that the sphere cannot be balanced thereon.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings in which: Fig. lisa schematic diagram of a cross-section of the intruder alarm with the key inserted in the housing; Fig. 2 is a sectional view taken along the line A-A of Fig. 1; Fig. 3 is a sectional view taken along B-B of Fig. 1; Fig. 4 is a sectional view taken along C-C of Fig. 1; Fig. 5 is a plan view of Fig. 1 taken in the direction D,and Figs. 6a, 6b are respective plan and elevational views of an extraction tool for use with the end plug ofthe housing.

Referring now to Fig. 1 the intruder alarm comprises an elongate metal housing 1 which is divided longitudinally into 3 sections, la, 1b and 1c which contain the battery power supply 2, the acoustic signal generator 3 and the switch 4 respectively.

The power supply 1a is separated from the acoustic signal generator 1b by a bulkhead 5a made of electrically insulating material and the generator section 1b and switch section 1c are separated by an electrically insulating material 5d.

At one end of the housing 1 there is an end cap 7 inserted which has 4 apertures 7a (Fig. 4) of rectangular shape located therein. A key 8 having 4 legs 8a is inserted into the housing through the cap 7, each leg 8a entering a respective aperture 7a.

The switch section 1c contains a switch 4 which comprises a steel ball of suitable dimensions which, with the device in the vertical position, rests on a stud 10, a small pillar of circular cross-section, recessed at the top 1 0a and formed of or clad with conducting material. The stud 10 together with a domed contact 11 on the inner side 7b of the cap 7 in the stitch are wired to one side of the acoustic signal generator 3. A conducting metal ring 12 is located around the inner periphery of the switch at approximately midway along the section length. The circular ring may be machined or stamped out or could be formed by a circular detent produced by cramping the case.

The ring 12 is connected to the negative side of the battery power supply 2 by the metal housing 1 or by a metal strip should the case be constructed of plastic.

The acoustic signal generator 3 is connected at the bottom end 3a to the positive terminal 2a of the battery power supply. The negative terminal 2b of the battery power supply connected to a plate 13a connected to a base end plug 13 which is insertable into the bottom end of the housing to retain the batteries therein.

The metal plate 13 contacts the inner surface of the metal housing 1 to provide a current path between the battery 2 and the ring 12.

The housing 1 ofthe device may be made of metal or plastic and the end plugs 13, 7 and interior bulkheads 5a Sb are plastic. A small ring 14 is attached to the outside ofthe housing atthetop ofthe switch section 1c through which a trip cord can be attached.

In use to activate or arm the device, the device is placed on its end Id on a level surface and the isolation key 8 is removed. This leaves the steel ball 9 balancing on the rim 10a of the recessed stud 10.

When the housing falls or vibrates due to movement the ball falls from the stud 10 and lies in the section 1c such that it is between the positive stud 10 and the negative ring 12 or between the domed contact 11 and the negative ring 12 completing an electrical circuit and activating the acoustic signal generator 3. The acoustic generator 3 continues to emit sound regardless of the future attitude of the device or of any subsequent further disturbance.

Thus if an intruder knocks the device vertical in its original position it will not be reset and the alarm continues.

The acoustic signal is switched off only by holding the device vertically up-side down and then pushing the key 8 into the switch section 1c. As the legs 8a of the key 8 are introduced through the apertures 7a in the cap 7, the tapered end 7b of the legs 7a centralise the steel ball 9 in the switch section which is then separated from the negative ring 12 thus interrupting the circuit. There is no other way of switching off the acoustic signal.

To prevent the unauthorised removal of the batteries 2 the base end plug 13 has a hexagonal or otherwise shaped recess 1 3b which requires a special 15 for removal which is suppiied with the unit.

The ring 14 or rings provided at the top of the housing 1 facilitates the attachment of trip string or wires, or for loose attachment to movable stock/windows/doors etc.

The number of legs, and apertures and the shape of adjacent legs and apertures may be varied to give a wide range of keys, so that only one key in many hundreds could reset a particular alarm, thus increasing the security offered. For example if any aperture or leg can be one of three basic shapes; square, circular or triangular and there are six apertures in the cap, then the number of combinations available is several hundred.

If required the device can be produced without the sonic unit or batteries and simply wired into a comprehensive alarm system. As a further alternative, the base end plug 13 could be omitted and the batteries inserted from one end only. The switch section 1c could be interlocking engaged or screwed into contact with section 1b using the key 8. The ring 12 or ball may be made of magnetic or magnetisable material such that in the non-equilibrium position or alarm mode there is improved adhesion between them to facilitate improved electrical contact.

Advantages of this device are that it is simple and relatively straightforward to produce; it is portable and can be located virtually anywhere; it cannot be switched off or reset by an intruder, and the resetting of different units can be made by individual keys which provides for greater security.

Claims

1. An intruder alarm comprising a housing adapted to be balanced in a position of equilibrium, said housing including acoustic signal generating means and power supply means, switch means located in said housing and adapted to be arranged such that when said housing is balanced in said equilibrium position said switch is off and when said switch is unbalanced, said switch is on permitting said power supply means to actuate the acoustic signal generator means.

2. An intruder alarm as claimed in claim 1 wherein said alarm means includes removable key means which is insertable into the housing, whereby when said key means is inserted, the switch means is switched off or reset.

3. An intruder alarm as claimed in claim 1 or claim 2 wherein said switch means comprises an electrical conducting element and two electrical contacts of different polarity, said electrical conducting element being balanced on the electrical contact when the housing is balanced the switch being off, and when said housing is unbalanced said electrical conducting element contacts each electrical contact.

4. An intruder alarm as claimed in claim 3 wherein the electrical conducting element is a sphere, and the electrical contact on which the sphere is supported when the switch is off is a cylindrical stud having a rim in which the sphere is seated when in the balanced position.

5. An intruder alarm as claimed in any one of claims 2-4 wherein, said key means has a plurality of generally parallel longitudinal legs, each leg being spaced around the periphery ofthe key and each leg having the same or a different cross-section.

6. An intruder alarm as claimed in any one of claims 2-5 wherein, said housing has a first end cap, the cap having a plurality of apertures located therein, each said aperture adapted to receive a respective leg of said key therein.

7. An intruder alarm as claimed in any one of claims 3-6 wherein, the first electrical contact is positive and second electrical contact is negative.

8. An intruder alarm as claimed in any one of claims 2-7 wherein the housing is electrically conductive, and being connected between said negative supply of the power supply means and said negative contact.

9. An intruder alarm as claimed in claim 7 or claim 8 wherein said negative contact is a ring located in the inner surface of said housing portion in which said switch means is located.

10. An intruder alarm as claimed in any preceding claim wherein, the other end of the housing has a removable end cap located therein, said plug having a shaped recess adapted to co-operate a shaped projection on plug extracting means.

11. An intruder alarm as claimed in claim 10 wherein the first end cap and the removable end cap of the housing are made of electrically insulating material.

12. An intruder alarm as claimed in any one of claims 6-11 wherein, the shape of the apertures of the first end cap and legs of the removable key means can be selected for co-operation.

13. An intruder alarm as claimed in any preceding claim wherein, ring means are provided at said one end of the housing for attaching a cord thereto.

14. An intruder alarm as claimed in any one of claims 7-13 said housing portion includes another positive electrical contact located opposite the first positive contact, the other electrical contact being shaped such that the sphere cannot be balanced thereon.