Patent Description:
Security monitoring systems for monitoring premises typically provide a means for detecting the presence and/or actions of people at the premises and reacting to detected events. Commonly such systems include sensors to detect the opening and closing of doors and windows, sensors in the form of movement detectors to monitor spaces for signs of movement, microphones to detect sounds such as breaking glass, and image sensors to capture still or moving images of monitored zones. Such systems may be self-contained, with alarm indicators such as sirens and flashing lights that may be activated in the event of an alarm condition being detected. Such installations typically include a central unit that is coupled to the sensors, detectors, cameras, etc. ("nodes"), and which processes receive notifications and determines a response. The central unit is typically linked to the various nodes wirelessly, rather than by wires, since this facilitates installation and also provides some safeguards against sensors/detectors effectively being disabled by disconnecting them from the central unit. Similarly, for ease of installation and to improve security, the nodes of such systems are typically battery rather than mains powered. Alternatively, a security monitoring system may include an installation at a premises, domestic or commercial, that is linked to a Central Monitoring Station (CMS) where typically human operators manage the responses required by different alarm and notification types. In such centrally monitored systems, the central unit at the premises installation typically processes notifications received from the nodes in the installation and notifies the Central Monitoring Station of only some of these, depending upon the settings of the system and the nature of the detected events. In such a configuration, the central unit at the installation is effectively acting as a gateway between the nodes and the Central Monitoring Station.

An important part of such security monitoring systems typically are the means for detecting the presence and/or actions of people or other detection targets, in particular moving objects. Commonly, such systems include motion sensors monitoring defined areas for signs of movement and imaging means to capture images or videos of a monitored area in the event that movement is detected.

In many commercially available security monitoring systems, passive infrared sensors (PIR) are applied for the purpose of motion detection. Such sensors typically comprise a sensor package, hermetically sealed, inside which there are typically a balanced pair of sensor elements which are exposed to IR radiation through one or more windows in the hermetic package. Typically, the PIR includes an optical arrangement, in the form of one or more lenses, that determines what the PIR sensor can "see" - e.g. how broadly, where, and how far. The lenses are typically provided in the form of Fresnel lenses. Generally, rather than using a single lens with a single focal length, an array of lenses with a range of different focal lengths are used, so that the PIR can "see" across a range of areas. Fresnel lenses and Fresnel lens arrays are attractive for this application because they can be made small and thin, so that they can be very compact. They can also be moulded from cheap plastic, meaning that the cost of the PIR can be kept down. Although moulded plastics Fresnel lenses are cheap and generally convenient, their optical performance can be adversely affected if they move relative to the sensor elements and if they are bent or otherwise deformed. Typically, being made of semi-soft plastics material, Fresnel lenses are easily damaged or distorted, changing and impairing their optical performance.

Movement sensors, such as PIR sensors, can be installed indoors or outdoors, for example to monitor rooms, entrances to dwellings such as houses or any or other area of interest. In order to avoid false alarms, it is desirable to restrict the monitoring area of the sensor to the area(s) of interest. At the same time, movement events of objects outside the area of interest should not result in activation of the security monitoring system. For example, when the movement sensor is installed to monitor a garden and a public path is located just beyond a garden fence, it would be desirable to prevent the movement sensor from being triggered by people walking along the public path.

However, the area of interest may significantly differ from application to application. Hence, a means for detection area adaption is required to ensure proper functionality of the system.

It is known that detection area adaption to specific applications can be achieved by precise adjustment of the mounting position of the sensor, both in terms of height and orientation (inclination to the vertical as well as azimuth) during the installation of the sensor, and/or by software means, for example programs which electronically regulate the sensor detectivity, during the commissioning of the security monitoring system. However, perfecting the positioning of the sensor and/or software calibration often requires extensive trial and error approaches and is consequently very time-consuming and expensive. It is understandable that an installation engineer may not have the time and/or patience to invest the time and effort necessary for correct calibration, resulting in imperfect functionality of the security monitoring system. In consequence, the sensor may routinely generate false alarms (which are expensive for the system supplier/operator to deal with) and these may lead to the relevant sensor being disabled or even the whole security monitoring system being turned off.

<CIT> discloses a camera system to which different lens caps can be attached.

<CIT> discloses an apparatus with an infrared sensor and magnetic near field communication properties for monitoring activity in a selected area.

<CIT> discloses a motion detection system which can be mounted to a wall by means of a hinge which allows adjusting the orientation of the motion detector.

<CIT> discloses a network camera which has a camera unit mounted to a base in a pivotal manner, and a motion detector arranged in the base.

<CIT> discloses an intruder alarm with a passive infrared sensor mounted between a window or door and a blind, curtain or shutter. When motion is detected, the window or door is illuminated. The light may be white or coloured, steady or pulsing. In addition an audible alarm, paint or dye canister, camera or external alarm system may be used.

Hence, there is a need to provide fast and cheap means for application specific detection area adaption of movement sensors for security monitoring systems.

The invention provides a kit of parts as defined in claim <NUM>, a sensor unit assembly as defined in claim <NUM> and a battery powered sensor unit assembly as defined in claim <NUM>.

According to a first aspect there is provided a passive infrared, PIR, motion sensor or a camera including a PIR sensor, having a plurality of different interchangeable covers or masks by means of which the field of view of the PIR sensor can be adjusted to suit a particular installation location.

Such a passive infrared, PIR, motion sensor or a camera including a PIR, may include a body which includes a lens or lens array for the sensing arrangement of the PIR, different interchangeable covers (or masks) of the plurality being mountable to and demountable from the body and being configured to cover different portions of the lens or lens array while leaving exposed another portion of the lens or lens array.

Preferably each of the covers or masks is mountable to the body in such a way as to avoid distorting at least the exposed portion of the lens or lens array. Preferably, when one of the interchangeable covers or masks is mounted to the body, the mounted cover or mask is spaced from the lens or lens array by an air gap.

Each of the interchangeable covers or masks may be configured as an end cap. The interchangeable covers or masks are preferably configured to be attached to the motion sensor or camera without the use of adhesives or screws. Preferably, each cover or mask is configured to clip to or snap fit to the motion sensor or camera.

Each of the interchangeable covers or masks may include a differently positioned or dimensioned aperture to expose only the selected portion of the lens or lens array.

The motion sensor or camera according to the first aspect preferably includes an anti-tamper arrangement configurable to trigger an alarm event in the event that a cover or mask secured to the sensor is removed from the sensor.

Each of the interchangeable covers or masks is preferably provided in the form of a self-supporting structure.

The body and each of the different interchangeable covers or masks may be injection moulded from a thermoplastic material. Preferably the body and the interchangeable covers or masks are injection moulded from polycarbonate.

An interchangeable cover or mask may be configured to accept one or more mask inserts to enable the interchangeable cover to be configured for a particular installation by, for example, masking both near and far zones otherwise monitorable by the motion sensing device. The interchangeable cover and the mask inserts may be configured to clip or snap fit together, preferably with the mask inserts located on an inner surface of the interchangeable cover so that they are only removable from the inner side of the cover.

According to a further unclaimed aspect there is provided a method of tuning a passive infrared, PIR, motion sensor to suit a particular installation location, the PIR including a lens or lens array to focus light onto the sensing arrangement of the sensor, the method comprising selecting a cover from a collection of a plurality of covers, each cover having a different configuration to expose a different portion of the lens array, the selected cover having being appropriately configured (e.g. appropriately positioned and dimensioned) to expose only a selected portion of the lens or lens array to restrict the field of view of the sensor to suit the particular installation location.

Each cover (which may also be termed a mask) may include a differently positioned or dimensioned aperture to expose only the selected portion of the lens or lens array.

Each cover may be configured to clip to or snap fit to the motion sensor.

According to a further aspect, there is provided a battery-powered sensor unit assembly according to claim <NUM>.

The motion sensor preferably includes an anti-tamper arrangement configurable to trigger an alarm event in the event that a cover secured to the sensor is removed from the sensor.

Optionally, the interchangeable covers are connected to the sensor unit by means of one or more connection elements, each comprising a first connection member positioned at the sensor unit and a second complementary connection member positioned at the interchangeable cover to be connected.

The interchangeable covers can be for example cheap and easy to attach injection moulded plastic parts with different shapes and/or sizes adapted to absorb or reflect incoming radiation, in particular infrared light. By selecting and connecting a suitable cover to the sensor unit, radiation emerging from locations outside of the area of interest can be blocked selectively, thereby calibrating the detection area in a purely hardware-based and time-efficient manner.

In an aspect, there is provided a kit of parts including a sensor unit assembly, comprising a sensor unit with image capture means configured to capture an image and/or a video of a monitored area and a motion detector, in particular a passive infrared, PIR, sensor, configured to detect motion in a detection area and to provide dependent on the detection a signal to activate the image capture means; and a plurality of interchangeable covers, each configured to be connected to the sensor unit, wherein different interchangeable covers are configured to restrict differently the field of view of the motion detector when connected to the sensor unit to restrict differently the field of view of the motion detector.

Optionally, the different interchangeable covers are configured to restrict differently the field of view of a motion detector by covering different parts of a lens or lens array of the motion detector when connected to the sensor unit.

Optionally the sensor unit, for example of the kit of parts, includes a battery compartment having a battery compartment cover, and the interchangeable covers are so configured that the covers can only be mounted to or removed from the sensor unit while the battery compartment cover of the sensor unit is absent, the interchangeable covers being securable to the sensor unit by securing the battery compartment cover to the sensor unit. The interchangeable cover(s) can thus be secured without the need for an additional fastening arrangement which may reduce moulding complexity and cost, while providing enhanced security of retention.

Optionally, the sensor unit, for example of the kit of parts, includes an anti-tamper arrangement for the battery compartment cover, the anti-tamper arrangement also providing anti-tamper protection for an interchangeable cover. In this way the interchangeable cover(s) is/are protected by an anti-tamper arrangement without the need to provide a further one in addition to that already provided for the battery compartment.

Optionally an interchangeable cover of the plurality of covers is configured to receive one or more shutter elements on an inner surface of the interchangeable cover prior to connecting the interchangeable cover to the sensor unit. In this way a cover can be configured appropriately for a particular situation while reducing the amount of material needed to provide a desired solution.

The interchangeable cover may be configured to couple to the or each shutter element through a snap fit interface arrangement. In this way, shutter elements may be coupled to the cover quickly and reliably without the need for further separate fastening elements and without the use of tools.

Optionally each of the plurality of interchangeable covers is configured to be connected to the sensor unit by means of a connection element, wherein the connection element comprises a first connection member positioned at the sensor unit and a second complementary connection member positioned at the interchangeable cover.

In a preferred embodiment, the connection element is a clip or snap connector. This allows fast and easy connection of covers to the sensor unit, in particular without the need for additional tools.

Typically, the motion detector comprises a lens array, in particular of a Fresnel type to focus incoming light from different zones or regions onto an active sensing part of the motion detector. In particular, the Fresnel lens allows influencing the beam path and shape of incoming radiation in a very space saving manner. In a simple arrangement, the Fresnel lens array can form an exposed surface of the motion detector.

Preferably, the lens array comprises multiple zones of different focal lengths. This allows focusing radiation from different locations or regions within the detection area to the sensor at different designated areas of the motion detector surface.

It is also conceivable that one zone of the lens or lens array forming an upper end of the motion detector surface has a long focal length, thus focusing light from parts of the detection area which are far away from the location at which the security monitoring system is mounted. Simultaneously, another zone of the lens or lens array forming a lower end of the motion detector surface can have a short focal length, thus focusing light from parts of the detection area which are close to the location at which the security monitoring system is mounted. The different zones can be sharply defined by abrupt changes of the lens geometry or smoothly transition into each other, such that the lens or lens array offers a continuous or nearly continuous focal length gradient.

In one variant of the kit of parts, the different interchangeable covers or masks are adapted to cover one or more different zones of the lens or lens array when connected to the sensor unit. Hence, zones of the lens array with certain focal length or focal length ranges can be selectively shaded and/or deactivated, thus decreasing substantially the intensity of light reaching the sensor from areas for which detection and/or monitoring is not required.

Advantageously, at least one interchangeable cover is adapted to cover a zone of highest focal length of the lens or lens array when connected to the sensor unit. By connecting this cover to the sensor unit, a maximum detection range can be defined and/or decreased.

In a further advantageous embodiment, at least one interchangeable cover is adapted to cover a zone of lowest focal length of the lens or lens array when connected to the sensor unit. This allows to selectively define and/or decrease detectivity in areas located close to the system.

In a simple arrangement of the kit of parts, the multiple zones of the lens or lens array with different focal length are spaced at different distances from the image capture means, wherein the zone located closest to the image capture means has the highest focal length. This allows installing the system at an elevated position, for example at a wall, such that the image capture means and zone of highest focal length are located above the zones of lower focal length.

In a preferred variant of a kit of parts according to an aspect, the covers are shaped such that when connected to the sensor unit a free space is formed between the cover and a lens or lens array of motion detector. Thus, direct contact between the cover and the lens or lens array of the motion detector is avoided. This reduces the risk of damaging the lens or lens array during connection or removal of covers, in particular in systems in which the lens or lens array is soft and/or otherwise readily deformable or readily damaged.

In a further embodiment, the kit of parts comprises a lid or shade for reducing illumination of the image capture means and/or motion detector. This is particularly useful for outdoor applications to protect the image capture means and/or motion detector from direct sunlight. Such a lid or shade may also be useful in internal settings where incandescent lights or other sources of significant quantities of IR energy, such as ovens, furnaces, or other industrial plant, are present.

In another preferable variant, the kit of parts comprises an anti-tamper means configured to prevent removal of interchangeable covers connected to the sensor unit without triggering a tamper signal. It is conceivable that a villain or other unauthorized subject might want to remove the cover so that the detection area and/or detectivity of the motion detector is increased and the system is triggered by harmless movements, eventually provoking an operator to either learn to ignore alarm signals or to simply disable the system. An anti-tamper means triggering an electrical signal upon unauthorized removal of the cover, thereby inducing an alarm or starting the image capture means, can prevent such situations and increases the overall security for the operator.

According to an aspect, there is also provided a sensor unit assembly, including one or more interchangeable covers connected to the sensor unit, assembled from a kit of parts. There is further provided a security monitoring installation comprising one or more such sensor unit assemblies.

There is also provided a security monitoring installation comprising one or more passive infrared, PIR, motion sensors or cameras including a PIR sensor, having a plurality of different interchangeable covers by means of which the field of view of the PIR sensor can be adjusted to suit a particular installation location.

Further advantages and features will become apparent from the following description of the invention and from the appended figures, which show nonlimiting exemplary embodiments of the invention and in which:.

<FIG> schematically shows a first embodiment of a sensor unit <NUM>, for a security monitoring system particularly for indoor applications.

The sensor unit or node <NUM> comprises a security monitoring unit <NUM> with image capture means <NUM>, such as a camera including an image sensor, configured to capture an image and/or a video of a monitored area and a motion detector <NUM>. In the depicted embodiment, the motion detector <NUM> comprises a passive infrared (PIR) sensor, configured to detect motion in a detection area and to provide dependent on the detection a signal to activate the image capture means <NUM>. The PIR sensor includes a Fresnel lens array <NUM> behind which are located the sensing elements of the PIR sensor. As the skilled person will appreciate, other technologies may be used to provide motion sensing, for example microwave sensing, and these likewise may benefit from the application of the inventive idea of providing a plurality of interchangeable covers or masks to "tune" the area "seen" by the motion sensor or motion sensing arrangement. Therefore, unless the context clearly requires otherwise, the invention as described and claimed is also to be taken to embrace both optical, e.g. PIR motion sensing, and non-optical, e.g. microwave, motion sensing. However, for battery-powered sensor units the use of a passive sensor such as a PIR is preferred because the use of such sensors can contribute to an attractively long battery life for the sensor unit - which is typically very important for security monitoring systems.

Furthermore, the security monitoring unit <NUM> has a housing within which the image capture means <NUM> and the motion detector <NUM> are located. In the embodiment, the housing is an injection moulded plastic part with openings that allow radiation to reach the sensors of the image capture means <NUM> and the motion detector <NUM>. More details of the structure of examples of the housing are described below with reference to <FIG> and <FIG>.

The sensor unit or node <NUM> furthermore comprises a plurality of interchangeable covers <NUM>, which may also be considered to be masks, each configured to be connected to the security monitoring unit <NUM>. All interchangeable covers <NUM> are differently configured so that they cover different parts of the lens array <NUM> when connected to the security monitoring unit <NUM>. For example, different covers may be provided with differently positioned apertures and/or differently sized apertures, to expose different parts of the lens array, thereby providing different fields of view for the sensing elements of the motion sensor.

The interchangeable covers may be connected or secured to the security monitoring unit <NUM> by means of a connection element. Additionally, or alternatively, the covers may be secured to the security monitoring unit <NUM> by means of a removable housing element such as a battery compartment cover, as will be described further below. In an embodiment, the connection element may be a clip connector, in particular a snap-fit connector.

It is conceivable, that the housing of the security monitoring unit <NUM> comprises a first connection member of the connection element, in particular a notch being used as snap-in area.

Each of the interchangeable covers <NUM> may comprise a second connection member complementary to the first connection member. This can for example be a protrusion and/or cantilever adapted to snap in the above-mentioned notch when the respective cover <NUM> is pressed against the housing of the security monitoring unit <NUM>. The connection can be permanent, so that once fitted the cover cannot readily be removed subsequently, but is preferable removable so that, for example, various different covers can be tried to suit a particular installation, and the optimum one chosen.

Of course, a snap-in (or snap-fit) connection is only one example of a suitable connection element and not limiting the scope of the invention. Other fastening means, such as magnetic or screw connections can be applied. In the case that the device <NUM> includes a removable battery compartment cover, it is preferred that at least some of the fastening means are concealed behind the battery compartment cover when the device is fully assembled - thereby improving retention security for the motion sensor mask/cover.

In the example depicted in <FIG>, a cover <NUM> for indoor surveillance is selected and connected to the security monitoring unit <NUM>. The cover <NUM> has an opening, aperture or cut-away through which incoming radiation can reach the motion detector through the lens array <NUM>. In the <FIG> example, the opening or aperture in the mask is so sized and located that the entire lens array surface <NUM> is exposed. Consequently, the motion detector <NUM> is not shaded by the selected cover <NUM> and the sensor unit or node <NUM> works with the full detection area intrinsic to the motion detector <NUM>. In this case, the cover <NUM> may mask an otherwise visible first connection element of the housing, and/or other structural features resulting in improved appearance of the sensor unit or node <NUM>. Alternatively, it is possible that no cover is connected to the security monitoring unit <NUM> in order to exploit the full detection range offered by the motion detector <NUM>.

In this <FIG> example, the security monitoring unit <NUM> is a mains powered device, the power supply cable <NUM> being visible in the bottom left of the Figure. It is of course possible to have a battery-powered indoor surveillance camera, and equally it is possible to install an indoor surveillance camera in an internal location where it may be useful to mask.

A second embodiment of a sensor unit or node <NUM> is shown in the <FIG>. The second embodiment largely corresponds to the first embodiment, so that only the differences will be discussed below. Identical and functionally identical parts are provided with the same reference symbols.

In each of the <FIG> a different cover <NUM> is selected and connected to the security monitoring unit <NUM>. The different covers <NUM> shade different parts of the lens array <NUM>, thereby defining different detection areas specific for the intended application.

In the described embodiment, the covers <NUM> are shaped such that in an assembled state a free space between them and the lens array surface <NUM> is formed. The free space can be for example a narrow gap (e.g., an air gap) between the cover <NUM> and the lens array surface <NUM> to avoid direct contact albeit ensuring proper masking.

<FIG> schematically shows a side elevation of a sensor unit, corresponding to a sensor unit <NUM> as shown in any of <FIG>, with its battery compartment cover <NUM> and motion sensor cover <NUM> removed. The unit <NUM> has an internal compartment <NUM> (not shown) to receive a battery or battery pack <NUM>, the battery preferably being rechargeable although a battery pack may be provided to enable the use of, for example, a plurality of standard alkaline cells. Provision may also be made to locate a power supply within the battery compartment and for a power supply lead to enter and extend from the battery compartment so that the power supply may be connected to an external source of power such as a mains electricity supply (as in the example shown in <FIG>).

The attachment of the battery compartment cover <NUM> (which may also be referred to as a lid, closure, closure element, or closure member) to the housing of the unit <NUM> is preferably provided with a tamper detection arrangement (also known as anti-tamper), so that once the unit is powered and registered within a security monitoring installation removal or attempted removal of the battery compartment cover causes the unit <NUM> to transmit a tamper signal to a control unit of the security monitoring installation which can then transmit an alarm event signal to a central monitoring station and/or cause the local sounding of a klaxon or other alarm indicator. In an example, an anti-tamper arrangement of the battery compartment cover may be used to provide an anti-tamper feature for the motion sensor mask <NUM> by requiring that removal of an installed mask <NUM> requires prior removal or release of the battery compartment cover <NUM>.

An example of such an integrated anti-tamper arrangement is shown schematically in <FIG>. Here, the motion detector masks <NUM> are so configured that, once installed and the unit assembled with the battery compartment cover <NUM> in place, the cover <NUM> cannot be removed without removing the battery compartment cover <NUM>. In the example shown a latching arrangement is provided to secure the battery compartment cover <NUM> releasably to the housing of the unit <NUM>. Projections in the form of tongues or hooks <NUM> extend from the open side of the battery compartment cover <NUM>, and these engage with corresponding features (not shown) provided in the housing of the unit <NUM>. A battery compartment cover release button <NUM> is provided to release the latching arrangement enabling the removal of the battery compartment cover <NUM>. Preferably, the latching arrangement is so configured that the battery compartment cover can be pushed into place, displacing the corresponding features in the housing which then snap back into place when the battery compartment cover <NUM> is in place, without requiring that the release button <NUM> be held depressed.

The sensor cover <NUM> is provided with protrusions, in the form of flanges, tongues, or fingers, that extend from the open end of the sensor cover <NUM>, and these cooperate with the battery compartment cover to lock the sensor cover in place once it and the battery compartment cover have been assembled to the housing. Preferably a relevant protrusion is formed on each side of the sensor cover <NUM> (so that a protrusion is provided for each of the two sides of the battery compartment (at least one either side of the battery). Each protrusion is also preferably formed with a hooked end or with an enlarged end, or some other suitable configuration, to better secure the sensor cover in place once the battery compartment cover is in place.

The sensor cover <NUM> and housing are also configured to reduce the risk that the sensor cover <NUM> can be prised away from the housing. To address this issue the sensor cover and housing preferably engage with each other over a large extent of their cooperating surfaces. In the example shown in <FIG>, the housing is provided with an outwardly facing groove or channel <NUM> on each side, and the motion sensor covers <NUM> are each provided with one or more corresponding male features, for example in the form of tongues or flanges, on respective inner edges. The motion sensor cover being mountable to and removable from the housing by engaging the male members with the open slots and then causing a relative sliding movement between the motion sensor cover <NUM> and the housing. In other words, the motion sensor cover <NUM> slides onto the housing, and into place on the sensor unit <NUM>, from an end of the sensor unit <NUM>. The motion sensor cover <NUM> can therefore be considered to be an end cap of the sensor unit (or at least of its housing).

When a motion sensor cover <NUM> is to be installed either for the first time or to replace a previously installed cover <NUM>, the battery compartment cover is lifted off after/while actuating the cover release button <NUM>. If a cover <NUM> is already installed this is removed, for example by sliding it laterally away from the battery compartment (i.e. linearly leftwards in the arrangement shown in <FIG>). The motion sensor cover that is to be installed is then slid on (from left to right in <FIG>) by engaging the male members with the respective open slots <NUM> and then pushing the cover <NUM> into place (up to the limit of its movement). Preferably, the slots <NUM> on either side of the housing are sections or segments of a single continuous slot that extends around the end of the housing intermediate the two slot sections, and one or more corresponding male protrusions is/are formed on a mating inner surface of the sensor mask <NUM>. In this way, an installed sensor mask may be more firmly and securely retained.

<FIG> schematically shows a frontal (or plan) view corresponding to <FIG>. The single continuous peripheral groove <NUM> mentioned as a preferred configuration is shown (as a dashed line) as including two opposed lateral segments <NUM>' and <NUM>", with a portion <NUM>‴ connecting the segments to make a continuous peripheral groove. The battery compartment <NUM> can also be seen, and within this are shown electrical terminals <NUM> for connection to corresponding terminals on the battery or battery pack <NUM>. Also shown are apertures <NUM> to receive the latch elements <NUM> of the battery compartment cover <NUM>. The anti-tamper sensing arrangement for the battery cover (and hence also for the sensor cover <NUM>) is provided within the housing behind (when viewed in <FIG>) the battery compartment. For example, one or more of the latch elements <NUM>, or some other protrusion of the battery compartment cover <NUM>, may be configured to make (or optionally break) a circuit in the installed position, the circuit status changing -and the change being detectable - when the battery compartment cover is displaced.

<FIG> shows a detailed illustration of the motion detector surface <NUM>. The motion detector <NUM> comprises a passive infrared (PIR) sensor and a Fresnel lens array <NUM> located at the motion detector surface <NUM> for focusing incoming infrared radiation onto the sensor.

The lens array <NUM> comprises multiple zones <NUM> of different focal length. Hence, light incoming from different regions within the detection area being differently spaced apart from the motion detector <NUM>, i.e. incoming with different incident angles, is focused by different zones <NUM> of the lens array <NUM> onto the PIR sensor.

In the described example, there are three zones <NUM> of different focal length being spaced at different distances from the image capture means <NUM>. In particular, the zone <NUM> of highest focal length, which is the upper zone <NUM> depicted in <FIG>, is located closest to the image capture means <NUM>.

The zone <NUM> located in the middle of <FIG> has intermediate focal length and the zone <NUM> located at the lower end of <FIG> has the lowest focal length.

In <FIG> a cover <NUM> is selected and connected to the security monitoring unit <NUM> which does not block any incoming radiation from reaching the sensor. Thus, movement of infrared emissive or reflective objects can be detected within the whole detection range intrinsic to the uncovered motion detector <NUM>.

In <FIG> a cover <NUM> is selected and connected that only covers the upper zone <NUM> of the lens array <NUM>. Hence, the intensity of radiation incoming from locations within the detection area further from the system <NUM> is reduced. Consequently, the maximum detection range is decreased to a desired value.

In <FIG> a cover <NUM> is selected and connected that covers both the upper and middle zones <NUM> of the lens array <NUM>. Hence, the detection range is further reduced.

It is also conceivable that only one cover <NUM> adapted to cover the zone <NUM> of lowest focal length is selected and connected to the security monitoring unit <NUM> to prevent activations of the sensor unit or node <NUM> by moving subjects in close proximity, in particular in spaces underneath of the installation and/or mounting position.

Furthermore, embodiments may be so designed that two covers <NUM> can be simultaneously connected to the security monitoring unit <NUM>, for example one covering the zone <NUM> of highest focal length and one covering the zone <NUM> of lowest focal length, such that only the zone <NUM> of intermediate focal length remains uncovered. An example of such a design is shown schematically in <FIG>. Here, a PIR sensor cover arrangement <NUM> is configured to permit separate cover elements to be secured within a cover to obscure different parts of a lens array of the PIR sensor. The cover <NUM> has an aperture <NUM> that optionally is so configured that when installed it exposes the full operating area of the PIR sensor (or, differently expressed exposes the full operating area of a lens array of the PIR sensor). The cover <NUM> is arranged to receive and retain separate cover elements <NUM> and <NUM>. Cover element <NUM> fits within a slot or socket <NUM> on an upper part of the inner side of the cover <NUM>. Cover element <NUM> likewise fits within a slot or socket <NUM> on a lower part of the inner side of the cover <NUM>. The cover elements <NUM> and <NUM> may be configured to be interchangeable - for example, they may be identical. However, the configuration of the cover and the lens array of the PIR detector may be such that cover elements to fit within the upper socket <NUM> must be differently configured to cover elements that fit within lower socket <NUM>, and vice versa.

Each of the upper and lower cover elements <NUM> and <NUM> may be provided in different sizes - that is covering more or less of the motion detector or its lens or lens array (if present), to enable different degrees of shading. Preferably, each cover element is clearly marked (preferably using an integral indication, for example moulded in to the cover element when it is injection moulded) to indicate the degree of shading - for example by indicating a range of distances obscured.

Preferably, the cover elements and their sockets are configured to achieve a snap fit, so that once installed a cover element is retained very securely within the cover. Preferably, however, the snap fit is releasable when the cover <NUM> is removed from the device <NUM>, so that an installed cover element can be removed optionally to be replaced with another cover element.

Although the embodiments illustrated in <FIG> are shown as including sockets <NUM> and <NUM> to receive the cover elements <NUM> and <NUM>, it will be appreciated that a kinematically equivalent arrangement, in which the cover elements are each provided with a socket (more generally female receptacle) to receive a respective protrusion (more generally male member) of the cover <NUM> could be used instead.

Also, both with configurations of the kind shown in <FIG> - in which a cover member <NUM> is configured to receive interchangeable shutters or masks <NUM> or <NUM>, and with configurations as shown in <FIG> - in which each cover member is differently configured (for example by defining a differently dimensioned aperture to mask different portions of the PIR detector or a lens array of a PIR detector), it is possible to provide arrangements in which the lateral extent of the "view" seen by the PIR sensor or by a lens array of a PIR sensor is similarly differently maskable to restrict the lateral extent of the operating field of a PIR sensor. Such an arrangement may, for example be helpful where a sensor device <NUM> is to be mounted in a position where a neighbouring property to one to be monitored is also in view. In such a situation one might typically endeavour to mount the sensor device <NUM> on an angled mount so that only the property to be monitored is within view of an image capture means of the sensor device and within view of the PIR sensor - but sometimes this is not possible. In such a situation, embodiments of the present invention which provide a way to restrict the lateral extent of the "view" of the PIR sensor can be useful.

An illustrative example of the expected detection area, respectively detection range of the sensor unit or node <NUM> with different covers <NUM> being attached to the monitoring unit <NUM> is provided in <FIG>. In this example, the sensor unit or node <NUM> is mounted at an installation height of <NUM> metres with a mounting angle of <NUM> degrees. Clearly, the ranges can be expected to increase if the installation height is increased, and reduced if the installation height is reduced. Similarly, tilting the sensor forwards away from the vertical will tend to reduce the detection ranges, while tilting the sensor backwards away from the vertical will tend to increase the detection ranges.

In case only the zone <NUM> of longest focal length is covered, no activation of the motion detector <NUM> is expected for objects moving at a distance greater than <NUM> metres. This distance is indicated with the solid line <NUM>.

In case the zone <NUM> of highest and intermediate focal lengths are both covered, no signal is expected for objects moving at a distance greater than <NUM> metres. This distance is indicated with the second solid line <NUM>.

For indoor applications, the detection range can be smaller, for example due to reduced ambient stray light, which also contributes to the total amount of infrared light reaching the sensor.

It is conceivable that the indoor detection range is <NUM> metres with the zone <NUM> of highest focal length being covered, as indicated by the first dashed line <NUM>, and only <NUM> metres if the zones <NUM> of highest and intermediate focal length are both covered, as indicated by the second dashed line <NUM>.

Unlike in the first embodiment of the security motion system assembly <NUM> for indoor applications, the second embodiment for outdoor applications as shown in <FIG> has first and second sunshades or lids <NUM> to protect respectively the image capture means <NUM> and the motion detector <NUM> from direct sunlight. Direct sunlight can result in overexposure and saturation of optoelectronic sensors used in cameras and motion detectors and may even reduce their lifetime. Furthermore, sunlight has a significant share of infrared radiation. Hence, direct solar illumination and/or moving clouds could result in triggering of the PIR sensor. These effects can be avoided with the sunshades or lids <NUM>. The use of a "sunshade" may also be appropriate in some internal installations - particular those where high-power incandescent lights or other powerful emitters of infrared radiation (such as infrared heaters) are mounted at a level above the installation level of a sensor unit or node <NUM> according to an aspect of the present invention.

In the illustrated embodiments, the motion detector sunshades <NUM> are integral with the covers <NUM> to avoid competition of assembly space, although this is of course optional.

Furthermore, the embodiments the sensor unit or node <NUM> may further comprise anti-tamper means configured to prevent removal of interchangeable covers <NUM> connected to the security monitoring unit <NUM> without triggering a tamper signal. The anti-tamper means can for example comprise an electrical contact formed between the security monitoring unit <NUM> and the attached cover <NUM>. In case the cover <NUM> is removed, an electrical signal is triggered that can starting an alarm and/or the image capture means <NUM>.

Alternatively, covers <NUM> can be fixed to the security motion unit <NUM> by magnetic connectors. Particularly in this configuration, the anti-tamper means can be a sensor stimulated by changes in a magnetic field resulting from unauthorized removal of the cover <NUM>.

Of course, also motion detector types and designs other than described above can be applied, such as for example microwave.

The above-described sensor unit or node assemblies <NUM> in their respective assembly states as shown in the <FIG> are installed using a method, which will be described in the following.

In a first step of the method, a suitable cover <NUM> is selected from a plurality of different interchangeable covers <NUM> depending on a desired detection area and/or detection range of the sensor unit or node <NUM>. As described above, the different interchangeable covers <NUM> are adapted to each cover different zones <NUM> of the motion detector surface <NUM> of the security monitoring unit <NUM>.

In a second step, the selected interchangeable cover <NUM> is connected to the security monitoring unit <NUM>, for example by means of one or more connection elements - or using an arrangement such as that illustrated schematically in <FIG> and <FIG>, where the cover or mask <NUM> is retained in position, at least in part, by a battery compartment cover. In some of the described embodiments, this is achieved by gently pressing the cover <NUM> against the security monitoring unit <NUM>, such that the complementary connection members located at the cover <NUM> and the security monitoring unit <NUM> connect to each other, in particular snapping into each other. In other described embodiments the cover or mask <NUM> may be slid into place, and then retained by engaging a battery compartment lid or closure- although there may in addition be a snap fit arrangement whose operation is such as to provide clear tactile or audible feedback of the engagement of corresponding parts of the cover/mask <NUM> and for example the housing of the device.

It is conceivable that a user (or, more typically, an installation engineer) performs the second step, advantageously the first and second step, during installation of the sensor unit or node <NUM> at a building structure. This reduces the overall effort for setting up the sensor unit or node <NUM> because installation at a building structure typically anyhow requires a user interaction. Additional time-consuming system calibration is not required.

It is contemplated that, for example, a kit of parts according to an aspect of the invention would be supplied with a set of a plurality of interchangeable covers/masks, each having a clearly visible indicator or legend (e.g. A, B, C, D, E, F), together with one or more charts or tables that indicate the effective range (maximum, minimum) of the motion sensor - when the motion sensor is mounted (vertically) at specified heights - e.g. <NUM>, <NUM>. <NUM> metres, etc. In addition, the sensor unit (or kit of parts) may also be supplied with adapters or mounting elements that permit the fixing of the sensor unit at a known angle from the vertical (typically enabling the sensor unit to be angled downwards at a known offset from the vertical (e.g. <NUM>, <NUM>, <NUM>, <NUM> degrees) - and suitable charts or tables provided showing the effective range of the motion sensor resulting from the use of the different masks (e.g. A, B, C, D, E, F) with the different angled adapters. IN this way, the installation engineer can readily determine what combination of elements to combine to achieve the motion desired range for any particular installation.

Especially in indoor applications, where the detection space is typically confined by walls, it is also possible to select zero covers <NUM> or a cover <NUM> which does not shade the motion detector surface <NUM>.

In case confinement of the detection space in not sufficiently provided by the surrounding environment itself, selection and connection of a suitable cover <NUM> is applied to precisely define the detection area, thus avoiding undesired triggering events.

As shown in the <FIG>, it is possible to select and connect a single cover <NUM> for masking one or multiple zones <NUM> of the motion detector surface <NUM> or lens array <NUM>.

However, dependent on the application, it can be beneficial to install two covers <NUM>, in particular when different areas of the motion detector surface <NUM> spaced apart from each other are intended to be covered, for example using a configuration such as that illustrated in <FIG>.

Claim 1:
A kit of parts including a sensor unit assembly, comprising
a sensor unit (<NUM>) comprising a security monitoring unit (<NUM>) with image capture means (<NUM>) configured to capture an image and/or a video of a monitored area and a motion detector (<NUM>), configured to detect motion in a detection area and to provide dependent on the detection a signal to activate the image capture means (<NUM>); and
a plurality of interchangeable covers (<NUM>), each configured to be connected to the sensor unit (<NUM>), wherein different interchangeable covers (<NUM>) are configured to restrict differently the field of view of the motion detector (<NUM>) when connected to the sensor unit (<NUM>).