A security system and associated methods

Abstract

A security system 100 comprises a first sensor 110 and a magnet 120. The first sensor 110 is mounted to a frame 14 of an openable door or window, whilst the magnet 120 is mounted to a leaf 12. The fir

Description

Field of the Invention The present invention relates to security systems for windows and doors. The invention also relates to methods for calibrating and methods employing such systems or devices. Background to the Invention Detection systems that detect whether a door / window has been opened are available. The vast majority of these known detection systems employ reed switch assemblies, each comprising a magnet and a reed switch. The magnet is installed onto the leaf and the reed switch onto the frame, or vice versa. The reed switch is activated when the magnet is proximate to the reed switch (i.e. when the door / window is closed). A disadvantage with such systems is that they are very easy to defeat by intruders. An intruder can tamper with a reed switch assembly simply by placing any off the shelf generic magnet close to the reed switch. This gives the monitoring system a false reading to report that the window or door is closed and secure. Therefore an intruder wishing to break into a building can place or affix a generic magnet close to the reed switch to signal to the monitoring system that the window / door is closed. The leaf can then be opened without the reed switch detecting that the magnet on the leaf has moved away from the reed switch. Summary of the Invention A security system for a window or door assembly and a method of detecting if an extrinsic magnetic field generator has entered the proximity of a security system for a window or door assembly are provided herein according to the appended claims. Also described herein is a method of calibrating a security system for a window or door assembly, the security system comprising a first magnetic field generator and a first sensor for sensing a magnetic field, one of the first magnetic field generator and first sensor being mounted to a moveable element of the window or door assembly, the other being mounted to a reference structure that the moveable element is moveable relative to, the method comprising: receiving an output signal from the sensor when the moveable element is in a first position, using said output signal to derive a location point in a reference coordinate system corresponding to said position of said moveable element, and defining at least a first bounding space in the reference coordinate system, said location point being within the bounding space. The security system may be used to monitor the position of the moveable element of the window or door assembly. The method of calibrating the security system is preferably an in-situ method of calibrating the security system. In other words, during calibration the moveable element is moved and the corresponding output signals of the sensor are recorded after the window or door assembly has been installed in a building at a particular geographical location. This contrasts from security systems which are set up ready for use during fabrication in a factory and prior to installation in a building. The bounding space defines a predefined error tolerance for the security system. Whilst expensive magnetometers would allow very accurate determination of relative position of the corresponding magnet, by defining a bounding space in a reference coordinate system, lower cost sensors may be employed. The defined bounding space will suitably take account of noise, such as digital noise, environmental temperature etc which could affect the output signal from the sensor. The output signals from the sensor suitably comprise digital signals associated with a measured magnetic field. The method may comprise positioning the moveable element and receiving an output signal from the sensor at each of at least a first and second position of the moveable element, using said output signals to derive a location point in a reference coordinate system corresponding to each said position of the moveable element, and defining at least a first bounding space in the reference coordinate system, said location point being within said bounding space. The method may comprise positioning the moveable element and receiving an output signal from the sensor at each of a plurality of positions of the moveable element, using said output signals to derive a location point in a reference coordinate system corresponding to each said position of the moveable element, and defining at least a first bounding space in the reference coordinate system, said location point being within said bounding space. By reference to location points being with in the bounding space, this may include one or more location points being on the boundary of the bounding space. Preferably the method is carried out in-situ. The method of calibrating the security system is carried out onsite, at the location where the window or door assembly has been installed. Preferably an output signal from the sensor is received when the moveable element is in each of a plurality of positions and a location point in a reference coordinate system is derived from the output signal corresponding to each said position. The security system may be calibrated by moving the moveable element between at least two, or a series of, discrete positions and registering the output signal from the sensor for each position. Alternatively the method may be configured to continuously record output signals from the sensor as the moveable element moves along a continuous path between a start position and a finish position. In the latter embodiment, the method may be configured to continuously record output signals from the sensor as the moveable element moves along more than one continuous path. Calibration parameters are established using the registered output signals from the sensor which correlate the measured magnetic field output from the sensor with location points in the coordinate reference system. Following calibration of the security system, when the security system is in a monitoring mode in which the position of the moveable element can be determined, the calibration parameters are applied to the output signals from the sensor to determine the position of the moveable element. The method may include a step of using at least one characteristic relating to the window or door assembly as an input in determining the calibration parameters. The method may include a step of a user inputting data regarding at least one characteristic relating to the window or door assembly as an input in determining the calibration parameters. Said at least one characteristic may be the type of window or door assembly (e.g. casement window, tilt and turn window) and / or a dimension of the leaf. For a casement window, the dimension of the leaf from the hinged edge to the edge that engages the jamb may be input into the system for example. Input of such a dimension assists in extrapolating expected output values of the sensor when the leaf is at or near a fully open position, even if the leaf was not registered at such an extent of opening during the calibration process. This means that the same system can more easily be used with different sizes of leaf. Preferably the step of defining at least a first bounding space in the reference coordinate system comprises defining a bounding form around each location point in the reference coordinate system that has been derived from an output signal of the sensor, each location point falling within its corresponding bounding form. The bounding form is preferably a 3D shape (i.e. a bounding shape), but may alternatively be a 2D shape, such as a planar square, ellipse or circle, or a 1D line. Preferably the calibration method involves defining a series of overlapping bounding forms that define a single bounding space. Preferably each bounding form comprises a cuboid shape. The bounding form may alternatively be any other 3D shape, such as an ellipsoid. Preferably the bounding form comprises a cube. Preferably the method further comprises the step of recalibrating the security system to take account of changes in the Earth’s magnetic field. In preferred embodiments the location points in the reference coordinate system are adjusted to modified location points based on expected changes in the corresponding magnetometer output signals due to changes in the Earth’s magnetic field. For example, modified location points may be derived by adding or subtracting new magnetic drift data from the output signals used to calculate the previous location points. In preferred embodiments adjusted bounding spaces are defined in the reference coordinate system based on the adjusted location points. The security system may be configured such that recalibration takes place automatically (i.e. the security system self-recalibrates). The security system may be configured such that recalibration takes place periodically at regular predetermined intervals. For example, the security system may be configured to recalibrate once every year. The security system may also I alternatively be configured to recalibrate if the polar drift has exceeded a predetermined threshold since calibration or recalibration last took place. According to a further aspect of the invention there is provided a program for carrying out a method according to any aspect of the invention as described above. Also described herein is a computer-read able medium storing a program according to any aspect of the invention. Also described herein is a security system for a window or door assembly, the security system comprising a first magnetic field generator and a first sensor for sensing a magnetic field, one of the first magnetic field generator and first sensor being mounted to a moveable element of the window or door assembly, the other being mounted to a reference structure that the moveable element is moveable relative to, the system further comprising a processing device configured to execute instructions to: receive an output signal from the sensor when the moveable element is in a first position, use said output signal to derive a location point in a reference coordinate system corresponding to said position of said moveable element, and define at least a first bounding space in the reference coordinate system, said location point being within the bounding space. The processing device may be a server, a computer, or a mobile communication device for example. The processing device may alternatively comprise electronic circuitry configured to execute the relevant instructions. The processing device preferably has a memory for storing instructions relating to operation of the security system. The processing device may be configured to execute instructions to allow the security system to be calibrated according to any aspect of the method of calibrating a security system as described above. Also described herein is a security system for a window or door assembly, the security system comprising a first magnetic field generator and a first sensor for sensing a magnetic field, one of the first magnetic field generator and first sensor being mounted to a moveable element of the window or door assembly, the other being mounted to a reference structure that the moveable element is moveable relative to, the system further comprising a processing device configured to execute instructions to: receive an output signal from the sensor when the moveable element is in a first position, use said output signal to derive a location point in a reference coordinate system corresponding to said position of said moveable element, and define at least a first bounding space in the reference coordinate system, said location point being within the bounding space, the system being adapted for calibration using a method according to any aspect of the invention described above. The system is preferably configured to allow a user to input data relating to at least one characteristic of the window or door assembly. Said data may relate for example to the type of door or window assembly and / or a dimension of the door or window assembly. The system may include a user interface for inputting at least one dimension of the leaf or it may include a programming port for receiving an input relating to a dimension of the leaf. The user interface may include a data input interface. The data input interface may be a key pad or touch screen or other suitable interface. Said data relating to at least one characteristic of the window or door assembly may be input by means of inputting a reference code to the system via a user interface, said reference code corresponding to parameters relating to window or door assembly characteristic stored in the system. In the method of detecting if an extrinsic magnetic field generator has entered the proximity of a security system for a window or door assembly according to an aspect of the invention, the security system comprises a first magnetic field generator and a first sensor for sensing a magnetic field, one of the first magnetic field generator and first sensor being mounted to a moveable element of the window or door assembly, the other being mounted to a reference structure that the moveable element is moveable relative to, the method comprising: receiving an output signal from the sensor, the signal being associated with a measured magnetic field, deriving a sensed location point corresponding to the output signal in a reference coordinate system, determining whether the sensed location point falls within a predetermined bounding space defined in the reference coordinate system, the predetermined bounding space having been derived based on at least one output signal obtained from the sensor during a prior calibration process; and generating an alert signal if the sensed location point falls outside the predefined bounding space. The method is intended to detect if an extrinsic magnetic field generator, such as an unauthorised magnet, is brought into the vicinity of the sensor. The calibration parameters established during the calibration process can be applied to an output signal from the sensor to determine what location point in the reference coordinate system the output signal correlates to (and this is the sensed location point derived from the sensor output signal). If the sensed location point derived from the output signal is outside the predefined bounding space, then this indicates that an extrinsic magnetic field generator has entered the vicinity and therefore that an intruder may be attempting to tamper with the security system and an alert signal is generated to alert the user. The predetermined bounding space may have been derived based on at least two output signals obtained from the sensor during a prior calibration process. The prior calibration process may be a method according to any aspect of the calibration method described above. Preferably the system is configured to operate in a monitoring mode, wherein the system only monitors for an extrinsic magnetic field generator when the system is in its monitoring mode. Other modes that the security system can run in including a standby mode or a calibration mode, the security system being run in calibration mode during calibration of the system. According to a further aspect of the invention there is provided a program for carrying out any method of detecting if an extrinsic magnetic field generator has entered the proximity of a security system for a window or door assembly as described above. The security system for a window or door assembly according to an aspect of the invention comprises a first magnetic field generator, a first sensor for sensing a magnetic field, one of the first magnetic field generator and first sensor being mounted to a moveable element of the window or door assembly, the other being mounted to a reference structure that the moveable element is moveable relative to, the system further comprising a processing device configured to execute instructions to: receive an output signal from the sensor, the signal being associated with a measured magnetic field, derive a sensed location point corresponding to the output signal in a reference coordinate system, determine whether the sensed location point falls within a predetermined bounding space defined in the reference coordinate system, the predetermined bounding space having been derived based on at least one output signal obtained from the sensor during a prior calibration process; and generate an alert signal if the output signal falls outside the predefined bounding space, the system further comprising, in addition to the first sensor, a magnetic proximity sensor, mounted to a moveable element of the window or door assembly or to a reference structure that the moveable element is moveable relative to. The system suitably further comprises means for generating an alert if the output signal falls outside the predefined bounding space. The magnetic proximity sensor, such as a reed switch, provides back-up monitoring for the security system. The reed switch may be mounted to the leaf or to the frame of the door or window assembly. Said magnetic proximity sensor has a normal state and an activated state, said magnetic proximity sensor converting to the activated state if a magnetic field is applied to the reed switch magnetic proximity sensor. The magnetic proximity sensor is configured within the security system such that if an extrinsic magnet is brought into close proximity of the magnetic proximity sensor, the magnetic proximity sensor will convert to its activated state. This indicates that an extrinsic magnet has been brought into proximity of the sensor. The system is configured such conversion of the magnetic proximity sensor to its activated state will generate an alert signal. This system thereby providing an anti-tamper alert system. Also described herein is a security system for a window or door assembly, the security system comprising a first magnetic proximity sensor and corresponding proximity sensor magnet, and a second magnetic proximity sensor, each magnetic proximity sensor having a normal state and an activated state, each magnetic proximity sensor converting to the activated state if a magnetic field is applied to the magnetic proximity sensor, the first and second magnetic proximity sensors both being mounted to one of a moveable element of the window or door assembly and a reference structure that the moveable element is moveable relative to, the proximity sensor magnet being mounted to the other of the moveable element and reference structure at a position such that when the moveable element is positioned directly adjacent the reference structure, the first magnetic proximity sensor is caused to be in its activated state and the second magnetic proximity sensor remains in its normal state. If an extrinsic magnet is brought into close proximity of the first and second sensors, both sensors will convert to their activated states. This indicates that an extrinsic magnet has been brought into proximity of the sensors, thereby providing an anti-tamper alert system. If said magnetic proximity sensor is a mechanical magnetic switch, such as a reed switch, the magnetic proximity sensor will convert to its activated state by the applied magnetic field causing the switch to close (for a normally open type switch) or to open (for a normally closed type switch). If the magnetic proximity sensor is a solid state magnetic proximity sensors then the magnetic proximity sensor may be configured to convert to its activated state if a magnetic field above a predetermined value is detected. Said predetermined value may be a predetermined factory setting. In such cases the system preferably further comprises a processing device configured to receive output signals from the second magnetic proximity sensor to determine whether the magnetic field sensed is above said predetermined value. Applying a magnetic field to said magnetic proximity sensor or sensors refers to application of a magnetic field over and above the ambient magnetic field. Preferably the system further comprises means for generating an alert signal if both the first and second magnetic proximity sensors are transitioned to their activated state. The system may comprise a plurality of magnetic proximity sensors. When the moveable element is positioned directly adjacent the reference structure, the first magnetic proximity sensor is caused to be in its activated state and the other magnetic proximity sensors remains in their normal state. The second and further magnetic proximity sensors may be arranged around the first magnetic proximity sensor. In such embodiments the system preferably further comprises means for generating an alert signal if the first magnetic proximity sensor and at least one of the other magnetic proximity sensors are transitioned to their activated states. Preferably all of the magnetic proximity sensors are housed together in a single housing. Preferably each magnetic proximity sensor is a reed switch. The magnetic proximity sensors in any of the embodiments in the present inventions may comprise other types of magnetic proximity sensor than reed switches or other types of mechanical magnetic switch. For example, solid state magnetic proximity sensors such as anisotropic magnetoresistive (AMR) sensors or Hall effect sensors may be employed as proximity sensors. Also described herein is a security system for a window or door assembly, the window or door assembly comprising a leaf moveable relative to a frame between closed and open positions, the security system comprising a magnetic proximity sensor mounted to the leaf or frame, said magnetic proximity sensor having a normal state and an activated state, said magnetic proximity sensor converting to the activated state if a magnetic field is applied to the magnetic proximity sensor, the system further comprising a processing device configured to receive output signals from the magnetic proximity sensor, the system further comprising means for generating an alert signal if said magnetic proximity sensor transitions to its activated state, the magnetic proximity sensor being positioned on the leaf or frame such that it does not align with any corresponding magnet on the other of the leaf or frame when the leaf is in its closed position. In preferred embodiments said magnetic proximity sensor is a reed switch, but it may be any other type of magnetic proximity sensor such as a one, two or three axis magnetometer or an AMR sensor. In prior art systems reed switches are ordinarily positioned on the leaf or frame such that they align adjacently with a corresponding magnet on the other of the leaf or frame when the leaf is in its closed position, causing the reed switch to transition to its activated state as a means for detecting whether the leaf is open or closed. In the present invention however, since the magnetic proximity sensor does not align in close proximity with any magnet when the leaf is in its closed position, the magnetic proximity sensor will not transition to its activated state when the leaf is in its closed position. The magnetic proximity sensor is therefore configured as a sensor for detecting whether an extrinsic magnetic field generator has been brought into proximity with the magnetic proximity sensor and the system is therefore configured to detect whether an intruder is attempting to tamper with the system. Also described herein is a security system for a window or door assembly, the window or door assembly comprising a leaf moveable relative to a frame between closed and open positions, the security system being configured to detect whether the leaf is in its closed or an open position, the security system including a first sensor for detecting whether the leaf has been moved or knocked, the security system further being configured to generate an alert signal if the system detects that the leaf has been moved or knocked whilst in an open position. By allowing activation of the sensor whilst the leaf is in its open position, the security system can detect whether the leaf has been moved or knocked whilst the leaf is open. This means that the security system can be armed even when the leaf is insecure (i.e. if the leaf is open). Typically in prior art building security systems, the system would check whether each monitored door or window is open as part of the arming process and if a door / window is detected to be open, the system would provide an alert to the user that a particular door / window is open. This gives the user a chance to close the open door / window before they leave the building or they can alternatively arm the system without closing the door / window, in which case the sensor for that door / window will not have been activated and will not monitor security of that opening and the security system is only partially armed. In the present invention, the security system is adapted to allow monitoring of a window or door whilst that window or door is open. This means that a window or door may be left open (for example a window may be left open in night vent position in order to air a building on a hot day) and the security system may nevertheless be fully armed to monitor every opening at which a sensor is located. Preferably the system further comprises a processing device configured to execute instructions to allow arming of said sensor whilst the leaf is in an open position. Preferably said first sensor is adapted for sensing a magnetic field. In some embodiments said sensor is a three axis magnetometer. Preferably said magnetometer is mounted to the leaf. In some embodiments the system further comprises a first magnetic field generator, one of said magnetic field generator and sensor for sensing a magnetic field being mounted to the leaf and the other being mounted to the frame. In other embodiments said first sensor is a vibration sensor. Preferably said vibration sensor is an accelerometer. In alternative embodiments said first sensor may be a rotary encoder. In some preferred embodiments the security system is adapted for monitoring the security of a window having a friction hinge. For example, the sensor, or any sensed element sensed by the sensor, is mounted to the leaf of a window, the leaf being coupled to the frame by a friction hinge assembly. Preferably the security system further comprises a window assembly comprising a leaf moveable relative to a frame between closed and open positions, the window assembly comprising a friction hinge assembly coupling the leaf to the frame. The friction hinge (also known as a friction stay) frictionally retains the leaf in an open position unless a force above a predetermined level is applied to move the sash from that open position. Additional force is therefore required to overcome the friction means. Frictional resistance is provided by the friction hinge so as to retain the window in a desired position, even when exposed to small forces, such as those created by the wind. Also described herein is a method of operating a security system for monitoring at least one window or door assembly, said window or door assembly comprising a leaf moveable relative to a frame between closed and open positions, the security system comprising means for detecting whether the leaf is in its closed position or an open position, the security system including a first sensor for detecting whether the leaf has been moved or knocked, the method comprising: arming said first sensor whilst the leaf is in an open position. Preferably the method comprises arming said first sensor whilst the leaf is in an open position. According to a further aspect of the invention there is provided a program for carrying out any method of operating a security system for monitoring at least one window or door assembly as described above. A program may be provided for carrying out any method as described herein. The security systems of the present invention preferably comprise wireless transmission means. The security systems of the present invention preferably comprise a first user interface. The security systems of the present invention preferably comprise a memory. The security systems of the present invention may further comprise a leaf moveable relative to a frame between closed and open positions. The sensor in any of the embodiments disclosed herein may be a one, two or three axis magnetometer. References herein to magnetometers may be to a one, two or three axis magnetometer. It will be understood that the terms leaf and sash can be used interchangeably. It will be understood that the terms processing device, processing means and processor can be used interchangeably. References herein to mounting of any first element to any second element encompass direct or indirect mounting (e.g. the mounting of the first element to a third element which is mounted to the second element). The phrase “in communication with” means “able to transmit signals to and / or receive signals from.” It is to be understood that the mere use of the term “first” does not require that there be any “second,” and the mere use of the term “second” does not require that there be any “third,” etc. Brief Description of the Drawings Embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a prior art system 10 for detecting whether a door / window is open or closed; Figures 2A to 2E illustrate diagrammatically a system and method for calibrating a security system according to one aspect of the invention; Figure 2A shows a security system according to an embodiment of the invention; Figure 2B shows diagrammatically boxes that may be defined in a reference coordinate system; Figure 2C shows a graphical representation of a set of bounding shapes that have been defined in a reference coordinate system; Figure 2D shows a basic flow diagram illustrating a method for calibrating the security system; Figure 2E is a functional block diagram showing some of the elements of the security system; Figure 2F shows a sensor module for the security system of Figure 2A; Figure 3 shows a security system according to a further embodiment for use in detecting possible tampering with the security system; Figure 4A shows a system for detecting whether an extrinsic magnetic field generator has entered the proximity of the security system; Figure 4B shows a sensor module for the system of Figure 4A; Figure 4C shows an alternative sensor module for the system of Figure 4A; Figure 5 shows a security system allowing arming of a sensor for monitoring a window / door when the window / door is open. Description of the Preferred Embodiments The present embodiments represent currently the best ways known to the applicant of putting the invention into practice. But they are not the only ways in which this can be achieved. They are illustrated, and they will now be described, by way of example only. Common features between the assemblies of the different figures are referenced by common reference numerals. Figure 1 shows a prior art system 10 for detecting whether a door / window is open or closed via a contact detection system. The prior art system employs a reed switch magnet 11 mounted to the moveable leaf 12 of a window and a reed switch 13 mounted to the window frame 14 (the reed switch magnet 11 and reed switch 13 may of course be mounted the other way around). Such prior art systems may be armed when the two parts (the reed switch and the reed switch magnet) come into close proximity with each other, indicating that the leaf is shut, which allows signalling to an alarm (i.e. a wider burglar alarm system) to switch on (i.e. to allow monitoring of the open / closed state of the window). These systems do not know whether the window has actually been locked, only that the leaf and frame are together. The reed switch is a very simple sensor which can be activated by any generic magnet. As discussed above, reed switch assemblies are therefore vulnerable to tampering using an extrinsic magnet. Other devices employed in prior art security systems include vibration sensors to detect hard knocks on a door / window that could indicate someone is attacking the door / window and to signal an alert (e.g. an alarm to sound or a notification to be sent to the homeowner). As with reed switch assemblies, a vibration sensor cannot detect whether a window / door has actually been locked, only whether a vibration has been sensed. Also, as with reed switch assemblies, vibration sensors in prior art systems can typically only be armed when the window / door has been closed. Figures 2A to 2F illustrate diagrammatically a system and method for calibrating a security system according to an aspect of the invention. Some of the basic elements of the security system are shown in Figure 2A. The security system 100 comprises a first sensor 110 and a magnetic field generator 120. One of the pair is mounted to the leaf 12 of an openable door / window and the other is mounted to the frame 14. In the embodiment in Figure 2A the magnetic field generator 120 is mounted to the leaf and the sensor 110 to the frame, but it will be understood that they could be mounted the other way around. The sensor and magnet assembly shown in Figure 2A may be part of a wider security system for monitoring a plurality of windows and / or doors. For example, a sensor and magnet pairs may be mounted at each of a number of external windows / doors of a property. The sensor 110 in this embodiment and in other embodiments described herein is preferably a magnetometer, which in preferred embodiments is a three axis magnetometer that is able to detect the position of the corresponding magnet in three coordinate axes. The three axis magnetometer will therefore output the sensed X, Y, and Z components of the magnetic flux vector present at the magnetometer. Two or one axis magnetometers may be employed instead however. In preferred embodiments the sensor 110 is housed in a sensor module 121, as shown diagrammatically in Figure 2F, the sensor module 121 comprising a housing 122 which contains the magnetometer 110, means to power the sensor such as a battery or batteries 123, and a communications module 124. The sensor module may also include a basic processor. The communications module allows output signals from the sensor to be transmitted wirelessly to a central processing device. The communications module may comprise RF transmissions means such as those using Bluetooth(RTM), Zigbee(RTM) or WiFi(RTM) communications standards for example. Output signals from the sensor 110 are received by a central processing device, which may be a dedicated processing device or may be a server, computer, or a mobile communication device for example. The central processing device is configured to execute instructions involved in calibration of the security system ready for use in security monitoring, the instructions being defined by programming instructions (such as a software or firmware program), which may be stored in a memory. The calibration method involves setting authorised magnetic field spaces, as will now be described. The system is operated in calibration mode initially when setting up the system and a monitoring mode when the system is being monitored. Figure 2D is a basic diagram illustrating the basic initial steps for calibrating the system. At 300, in order to calibrate the system the user places the system into calibration mode by providing a signal to a processor 24 using a user interface 23 (see also the schematic diagram in Figure 2E). In such embodiments, the system has a user interface for providing a signal to a processor within the sensor module to enter the calibration mode. Such a user interface may comprise a push button or a remote device with keypad or touchscreen etc such as a smartphone. Alternatively, the calibration mode may be entered automatically after a battery is first installed and / or when the sensor module switched on for the first time. Once the system is in calibration mode, at 301 the user is prompted by the system to position a moveable element (which in this case is the leaf 12) in a first predetermined position, such as a closed position, or an open position, via the user interface or some other indicator means. After the user has placed the leaf in the first predetermined position, at 302 the user provides an indication to the processor 24 via the user interface 23 that the leaf has been placed into the first predetermined position. Alternatively the indication that the leaf is in the predetermined position may be automatically derived by the system by determining that the magnetic field sensed by the magnetometer has been stable for a predetermined time period. At 303, the processor 24 then records one or more properties of the magnetic field produced by the magnet 120 as sensed by the magnetometer 110 and stores at least one of the properties or values derived therefrom in a memory 25. At 304-306, after the system has registered the leaf in the first predetermined position the steps repeat in relation to a second predetermined position as shown in Figure 2D. 09 10 23

Claims

1. A security system for a window or door assembly, the security system comprising a first magnetic field generator, a first sensor for sensing a magnetic field, one of the first 5 magnetic field generator and first sensor being mounted to a moveable element of the window or door assembly, the other being mounted to a reference structure that the moveable element is moveable relative to, the system further comprising a processing device configured to execute instructions to:receive an output signal from the sensor, the signal being associated with a 10 measured magnetic field,derive a sensed location point corresponding to the output signal in a reference coordinate system,determine whether the sensed location point falls within a predetermined bounding space defined in the reference coordinate system, the predetermined bounding space 15 having been derived based on at least one output signal obtained from the sensor during a prior calibration process;and generate an alert signal if the output signal falls outside the predefined bounding space,wherein the system further comprises, in addition to the first sensor, a magnetic 20 proximity sensor, mounted to a moveable element of the window or door assembly or to a reference structure that the moveable element is moveable relative to.

2. A security system according to claim 1, wherein said magnetic proximity sensor is a reed switch.

253. A security system according to claim 1 or 2, wherein the magnetic proximity sensor has a normal state and an activated state, said magnetic proximity sensor converting to the activated state if a magnetic field is applied to the magnetic proximity sensor.30 4. A security system according to any preceding claim, wherein the system isconfigured such that conversion of the magnetic proximity sensor to its activated state generates an alert signal.

5. A method of detecting if an extrinsic magnetic field generator has entered the 35 proximity of a security system for a window or door assembly, the security system09 10 23comprising a first magnetic field generator and a first sensor for sensing a magnetic field, one of the first magnetic field generator and first sensor being mounted to a moveable element of the window or door assembly, the other being mounted to a reference structure that the moveable element is moveable relative to, the security system further comprising, 5 in addition to the first sensor, a magnetic proximity sensor, mounted to a moveable element of the window or door assembly or to a reference structure that the moveable element is moveable relative to, the magnetic proximity sensor having a normal state and an activated state, the magnetic proximity sensor being converted to the activated state if a magnetic field is applied to the magnetic proximity sensor, the method comprising10 receiving an output signal from the sensor, the signal being associated with ameasured magnetic field,deriving a sensed location point corresponding to the output signal in a reference coordinate system,determining whether the sensed location point falls within a predetermined 15 bounding space defined in the reference coordinate system, the predetermined bounding space having been derived based on at least one output signal obtained from the sensor during a prior calibration process;and generating an alert signal if the sensed location point falls outside the predefined bounding space,20 and furthermore, generating an alert signal if the magnetic proximity sensor isconverted to its activated state.

6. A method of detecting if an extrinsic magnetic field generator has entered the proximity of a security system for a window or door assembly according to claim 5, wherein 25 the prior calibration process is a method comprisingreceiving an output signal from the sensor when the moveable element is in a first position,using said output signal to derive a location point in a reference coordinate system corresponding to said position of said moveable element,30 and defining at least a first bounding space in the reference coordinate system,said location point being within the bounding space.

7. A method according to claim 6, wherein the method is carried out in-situ.09 10 238. A method according to claim 6 or 7, wherein an output signal from the sensor is received when the moveable element is in each of a plurality of positions and a location point in a reference coordinate system is derived from the output signal corresponding to each said position.

59. A method according to any of claims 6 to 8, wherein the step of defining at least a first bounding space in the reference coordinate system comprises defining a bounding form around each location point in the reference coordinate system that has been derived from an output signal of the sensor, each location point falling within its corresponding 10 bounding form.

10. A method according to claim 9, wherein each bounding form comprises a cuboid shape.15 11. A method according to any of claims 6 to 10, wherein the method further comprisesthe step of recalibrating the security system to take account of changes in the Earth’s magnetic field.

12. A method of detecting if an extrinsic magnetic field generator has entered the 20 proximity of a security system for a window or door assembly according to any preceding claim, wherein the system is configured to operate in a monitoring mode, wherein the system only monitors for an extrinsic magnetic field generator when the system is in its monitoring mode.25 13. A method according to any preceding claim, wherein said magnetic proximitysensor is a reed switch14. A program for carrying out a method according to any preceding claim.30 15. A method or security system according to any preceding claim, wherein said sensoris a one, two or three axis magnetometer.

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