GB2399927A

GB2399927A - Security system using magnetic field

Info

Publication number: GB2399927A
Application number: GB0306412A
Authority: GB
Inventors: Jason Charles Udall
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-03-20
Filing date: 2003-03-20
Publication date: 2004-09-29
Also published as: GB0306412D0

Abstract

A security system is used to safeguard articles 12 displayed on a counter 10 in sales premises. The system comprises an electrical loop 14 surrounding the counter 10 and fed with a low frequency control signal to create a magnetic field over the counter 10. A monitoring device 18 responsive to the magnetic field is attached to each article 12 and arranged to operate an alarm if any such article 12 is moved out of the field. Each monitoring device is responsive to the magnetic field whatever its orientation, so articles 12 can be examined without causing a spurious alarm. The loop 14 may carry data signals for transmission to the monitoring devices, and voice messages to be broadcast may be delivered through a microphone 20. One or more other systems 22 may be arranged side-by-side, and the invention may be used for other purposes such as access control. The frequency of the control signal is lower than the frequency of the electrical mains.

Description

1. 2399927

SECURITY SYSTEM

This invention concerns security systems, particularly but not exclusively for guarding against unauthorised removal of articles from, or entry to a controlled space.

In sales premises it is common practice for display items to be laid out where customers can see them and try them, and such premises naturally need safeguards against theft, especially for high-value but readily portable items such as electronic equipment. One well-established means of safeguarding display items is a system in which the items are tethered by cables arranged in the form of a loop and an alarm sounds if the loop is broken. Apart from the fact that multiple cables can easily become untidy the tethering arrangement limits the amount be which any item may be manoeuvred for inspection by a customer.

It is an object of the present invention to provide a security system which is tidier and allows more freedom of movement (and is thereby more customer- friendly) than such previous loop systems.

Thus according to the invention there is provided a security system for monitoring movement of an article out of or into a controlled space, which security system comprises an electrical loop bounding the controlled space, a signal generator for applying to said loop an electrical control signal so as to create a magnetic field across the controlled space and a monitoring device associated with said article and responsive to said magnetic field, wherein the system includes an À e see e e Àe e e e e e À e e e e e e e _ _ e ee ese e e see e e À e e e e see en e e e alarm operable alternatively according to whether the monitoring device is within

or without said magnetic field.

To avoid interference inward (eg from other electrical equipment in the vacuity) or outward (eg with tnductvely-coupled hearing aids) it ts preferred that the control signal is at a frequency distinct from frequencies of other electrical apparatus in or around the controlled space. Preferably the frequency of the control signal is lower than the frequency of electrical mains power in or around the controlled space, and it may be 23Hz.

The control signal may be carried on a carrier signal, possibly of 25KHz, and it is preferably amplitude modulated.

The system may include a further signal generator operable to supply a further signal to the loop. This may be, for instance, for transmitting data to the monitoring device or for transmitting voice messages in or around the loop.

The monitoring device may be secured to an article to be safeguarded, and there may be a plurality of monitoring devices respectively associated with a plurality of said articles. Preferably the monitoring device is responsive to the magnetic field whatever the orientation of said article.

The security system may be used to safeguard display items in sales premises, or items for use by members of the public; or it may be used to monitor persons such as infants or elderly people who should stay within a controlled space or to guard against the unauthorized entry of people to some designated space; or it may be used with boats in a marina or cars in a car park etc. À À À À 3 c e À À Other aspects of the invention will be apparent from the following description, which is made by way of example only with reference to the accompanying schematic drawing in which Figure 1 is a plan view of a security system according to the invention as used in sales premises; Figure 2 is a plan view of a security system according to the invention as used to control personnel movement; Figure 3 is an isometric view of part of one form of monitoring device for use with the invention; and 10Figure 4 is an isometric view of part of another form of monitoring device for use with the invention.

Referring first to Figure 1, this shows a display stand or counter 10 in sales premises. The counter 10 supports a plurality of items 12 for display, which items 12 may be for instance hill or other high-value electronic equipment. The counter 1510 is surrounded by an electrical loop 14 to which a signal generator 16 applies a control signal, thereby to create a magnetic field across the space bounded by the loop 14. The control signal is a signal of 23 Hz, to avoid any likely interference with electrical apparatus in the vicinity, and is carried on a carrier frequency of 25KHz.

Attached to each item 12 is a monitoring device 18 responsive (by means to be described in more detail hereinafter) to the magnetic field created by the loop 14. Each monitoring device 18 is quiescent as long as the magnetic field is present, but an alarm sounds and/or flashes a warning if any monitoring device ceases to ce. e ee a 4 a. .ee a ce. e

detect the magnetic field. (For simplicity of illustration, the alarm is not shown in either Figure 1 or Figure 2, but those skilled in the science will be readily able to construct a suitable device).

It will now be understood that each article 12 can be freely picked up and examined by a customer but there will be an immediate warning if any attempt is made to remove any article 12 from the vicinity of the counter 10. And for additional security there will be a warning if the loop 14 is broken, since the

magnetic field will then be lost.

The signal generator 16 includes means for transmitting voice messages, which can be delivered by means of a microphone 20 for broadcasting to staff and/or customers within the loop 14.

The sales premises may include a plurality of similarly arranged security systems, of which another is indicated at 22 in Figure 1, and such system may be set up differently so as to keep controlled articles within areas allocated to them.

Figure 2 illustrates use of the invention for access control. A signal generator delivers a low frequency control signal to an electrical loop 32 bounding a controlled space 34 from which unauthorised personnel are excluded. Thus a magnetic field is created across the controlled space 34. Personnel carry a tag including a monitoring device responsive to the magnetic field, so that if they enter the controlled space 34 an alarm sounds and/or flashes a warning.

The system of Figure 2 can be configured in a reverse arrangement so that a warning is given if a person leaves the controlled space 34, and this arrangement e ee. e e me e e e e e e 5 e e ee e e e e e e see e. e e e may be used to safeguard infants in creches, for instance, or elderly or infirm people in nursing homes.

It will be understood that the magnetic field created by a loop will have lines of force which vary in direction across the space bounded by the loop. At the same time, customers inspecting article may well turn them into and out of line with the local lines of force. It follows that for effective security any monitoring device of the invention needs to be responsive to the magnetic field whatever the direction of the lines of force. One suitable arrangement is shown in Figure 3. In this, a monitoring device includes three coils 40, 42 and 44 arranged mutually orthogonally. If the (local) lines of force of the magnetic field are in the direction of arrows A, say, then a current will be created in coil 40, even though there may be little or no effect on coils 42 or 44. The three coils 40, 42 and 44 each give independent signals and outputs from them are amplified and fed to an OR-gate 46 which in turn is connected to an alarm control circuit 48. As long as any one of the coils 40, 42 and 44 detects the expected magnetic field, the alarm is suppressed.

But if none of the coils detects the magnetic field (which will happen if the magnetic field ceases for any reason or if the monitoring device is moved out of the

field) then the alarm will give a warning.

A simplified, and cheaper, arrangement is shown in Figure 4. This has a coil 50 arranged at 45 to each of the top 52, front 54 and side 56 of an article to which the monitoring device is attached. Thus, however the article is laid upon a counter, the coils 50 will respond to a generally vertical magnetic field B. The output from À À À a. . À À À . . À À ÀÀ À - 6 - À. ... . .. If.

À À À À À À Àe e. À À the coil 50 is amplified and delivered to an alarm control circuit 58 as aforcdescribed.

Monitoring devices as described with reference to Figures 3 and 4 are powered by a battery, not shown, and it will be understood that each can be moved in the controlled space defined for it, without triggering the alarm.

Various modifications may be made to security systems described herein without departing from the present invention. For instance, such a security system may be used to safeguard parked cars by laying a loop around the perimeter of a car park, and similarly boats may be safeguarded in a marina. Other uses and modifications will be apparent to those skilled in the science.

Claims

C I À b b cat e c 7 ec cee act À À À r

1 A security system for monitoring movement of an article out of or into a controlled space, which security system comprises an electrical loop bounding the controlled space, a signal generator for applying to said loop an electrical control signal so as to create a magnetic field across the controlled space and a monitoring device associated with said article and responsive to said magnetic field, wherein the system includes an alarm operable alternatively according to whether the monitoring device is within or without said magnetic field.

2 A security system as claimed in Claim 1 wherein the control signal is at a frequency distinct from frequencies of other electrical apparatus in or around the controlled space.

3 A security system as claimed in Claim 2 wherein the frequency of the control signal is lower than the frequency of electrical mains power in or around the controlled space.

4 A security system as claimed in Claim 3 wherein the frequency of the control signal is 23Hz.

A security system as claimed in Claim 4 wherein the control signal is carried on a carrier signal 6 A security system as claimed in Claim 5 wherein the carrier signal has a frequency of 25KHz.

7 A security system as claimed in Claim 5 or Claim 6 wherein the control signal is amplitude modulated.

t.C 4 c r À 4 4.

_ _ t À 4; _.

À C C. 8 A security system as claimed in Claim 7 wherein the control signal has a mark-space ratio of 50%.

9 A security system as claimed in any preceding claim including a further signal generator operable to supply a further signal to the loop.

10 A security system as claimed in Claim 9 wherein said further signal generator supplies data for transmission to the monitoring device 11 A security system as claimed in Claim 10 wherein said data is supplied serially by the further signal generator.

12 A security system as claimed in Claim 9 wherein said further signal generator supplies voice messages for transmission in or around the loop.

13 A security system wherein the monitoring device is secured to said article.

14 A security system as claimed in Claim 13 wherein the monitoring device is responsive to said magnetic field whatever the orientation of said article.

15 A security system as claimed in Claim 14 wherein the monitoring device comprises three field-ecsponsive coils arranged to be mutually orthogonal.

16 A security system as claimed in Claim 14 wherein the monitoring device comprises a field-responsive coil arranged at an angle to each of the top, front and side of said article.

17 A security system as claimed in Claim 16 wherein said angle is 45 .

À eece e e Àe e ee e ee e e e e e e e e e 9 e ce ace e e e see e e e e e a e see e. e e e 18 A security system as claimed in any preceding claim including a plurality of monitoring devices respectively associated with a plurality of said articles.

19 A security system as claimed in any preceding claim wherein the controlled space comprises sales premises and the or each said article is an item for display.

A security system as claimed in any of Claims 1 to 18 wherein the controlled space comprises a place accessible to the public and the or each said article is an item intended for use by members of the public within said place.

21 A security system as claimed in any of Claims 1 to 18 wherein the controlled space comprises a place wherein designated persons are required to remain and the or each said article is carried by a said designated person, and the alarm is operated if a designated person leaves that place.

22 A security system as claimed in any of Claims 1 to 18 wherein the controlled space comprises a place from which persons are excluded and the or each said article is carried by a said person, and the alarm is operated if such person enters that place.

23 A security system as claimed in any of Claims 1 to 18 wherein the or each said article comprises a vehicle of any kind and the controlled space comprises a place wherein such vehicle is to be left when not in use.

24 A security system as claimed in any preceding claim wherein the alarm is audible and/or visible and/or tactile.

À: À. A: I: À À À À À À À À - 10 - : À À * * À ' À À * À * À * A security system as claimed in any preceding claim wherein the monitoring device is powered by a battery.

26 A security system as claimed in (-,laim 25 wherein the monitoring device includes no switch and becomes operable as soon as said battery is connected thereto.

28 A security system substantially as hereinbefore described with reference to and as shown in the accompanying drawings.