GB2081454A - Monitoring human body movement - Google Patents

Abstract

Apparatus for monitoring infant body movement comprises a variable capacitance sensor 1, formed by a plurality of juxtaposed conductive sheets spaced apart by insulating sheets, which is placed adjacent the infant so that body movement varies the opening between the sheets. The resulting change in capacitance alters the frequency of an oscillator 26 connected via a frequency-voltage converter 27 to a voltage comparator 28 which produces an output only when there is no movement. An adjustable delay 34 prevents actuation of an alarm display 36, and optionally an audible alarm until there has been no movement for a preset time. Display 35 indicates whether movement is being detected. The sensor 1 comprises a stack of metal foil sheets each completely coated with plastics film and alternately connected to conductive fastening bolts in an insulating strip. <IMAGE>

Description

SPECIFICATION Movement detection and monitoring This invention relates generally to the detection and monitoring of human body movement, including the presence and/or absence of that movement and derivatives thereof, such as extent and rate of movement. In particular, the invention concerns a human body movement detecting and signalling device, and monitoring apparatus incorporating that movement detecting and signalling device to monitor the detected body movement. The detecting device, and monitoring apparatus may be used to detect and monitor body movement presence and/or absence of sleeping infants, and it will be convenient to hereinafter described the invention in relation to that example application.It is to be appreciated, however, that the invention is equally applicable to the detection and monitoring of other human body movement and derivatives and so should not be considered as limited to use in the example application.

A significant proportion of infant mortality, at least during the initial months of life, occurs as a result of so-called "cot death" of the sleeping infants. The causes of and reasons behind cot death remain unexplained although it seems to stem from the infant simply ceasing to breathe. That being so, it is considered that remedial measures, such as infant disturbance, taken during breathing cessation could avoid death. However, it is a matter of detecting that cessation and warning persons in charge of the infant so that the remedial measures are promptly taken.

With this purpose in mind, a variety of instruments have been developed to detect and warn of breathing cessation, although in general those instruments are relatively complex in construction and operation and thus expensive. As a result their use is usually confined to hospitals and infant welfare institutions and not individual homes where a majority of cot deaths occur.

One relatively simple monitoring instrument devised involves the use of an electro-mechanical transducer which is adapted to be placed adjacent the infant's body. The transducer includes a resiliently compressible pad adapted to produce low intensity noise upon compression or expansion in response to body movement and a microphone to detect the noise and signal the presence and/or absence of that noise. In a noise isolated environmentthatinstru- ment performs satisfactorily, but in environments of most desired use, such as individual homes, the microphone has been found to detect and signal noise other than that produced by the pad. The resulting misleading signal may be annoying at best and tragically fatal at worse.

It is an object of the present invention to provide a relatively simple human body movement detecting and signalling device which alleviates the foregoing disadvantages of prior instruments.

It is another object of the present invention to provide a relatively simple human body monitoring apparatus, which incorporates the movement detecting and signalling device, and which alleviates the foregoing disadvantages of prior instruments.

It is a further object of the present invention to provide a human body movement detecting and monitoring device and human body monitoring apparatus incorporating that device which may be particularly useful in detecting and monitoring body movement in sleeping infants.

According to one aspect of the present invention, there is provided a human body movement detecting and signalling device, including: a plurality of juxtaposed, relatively movable, electrically conducting sensor members, the sensor members connectable to an electrical power source and operable to generate an electrical spacing signal as a function related to the spacing between adjacent sensor members, construction and arrangement of the device being such that, in use, the sensor members are positioned adjacent a human body and respond to movement of that body by varying the spacing between at least two adjacent sensor members, thereby to alter the generated spacing signal and so signal movement of the human body.

Preferably, during use, the device is mounted directly on the human body whose movement is being detected. In that way the device moves generally with the body and presence and/or absence of movement of the body is mechanically transmitted to the sensor members of the device to respectively maintain and/or alter sensor member spacing in response thereto.

Preferably, in the device, the spacing signal is generated from the sensor members as a result of the electrical capacitance occurring between adjacent sensor members, changes in the member spacing altering that capacitance because of the relationship between capacitance and dimensions of adjacent sensor members acting as one or more capacitors. As a result the spacing signal generated is a measure of total capacitance between adjacent sensor members and is determined by the voltage or potential difference between those adjacent sensor members. Preferably, adjacent sensor members are electrically insulated from each other and alternate ones of the sensor members are electrically connected to each other to enable their acting as capacitors.

Preferably, the size, shape and number of the sensor members are selected according to criteria such as the desired detection sensitivity and desired physical appearance having regard to the precise intended application of the device.

Preferably, in the movement detecting and signalling device the sensor members are flexible and so are, at least, substantially freely and readily movable relative to each other. In this way, those members can be arranged to more easily conform to the shape of the human body thereby facilitating mounting thereon, and can better detect human body movement regardless of movement direction.

Preferably, the sensor members are stacked together in an overlying relationship, and are fastened together along a corresponding peripheral edge region so as to maintain the sensor members in their overlying relationship. In that regard the sensor members are preferably secured together to form, in effect, a pad of sensor members. Preferably, an elongated fastening member is provided and the sensor members are fastened to that fastening member to maintain them in their overlying relationship.

Preferably, in the movement detection and signalling device, the electrical power source is any suitable stable supply.

Preferably, the sensor members are in the form of sensor sheets. Each sensor sheet is, preferably, generally planar and has a peripheral edge. Preferably, each sheet includes an inner conducting lamina and outer insulating or dielectric laminae. The conducting lamina is, preferably, electrically connectable to the power source, whilst the insulating or dielectric laminae, preferably, maintains the conducting lamina of adjacent sensor sheets in insulated spaced apart relation, to enable adjacent sheets to act as capacitors. The adjacent sensor sheets may abut and/or be spaced apart from each other during use of the device.

Preferably, the detecting and signalling device further includes a connecting member for electrically interconnecting the sensor members to an indicator unit operable to receive the generated spacing signal and respond thereto by providing an indication of human body movement.

Preferably, the detecting and signalling device is provided with a containerforthe protective housing of the sensor members. That container is preferably flexible, to allowtransmission of human body movement therethrough to the sensor members.

Preferably, that container is also waterproof and capable of being maintained in a clean condition. In that regard, the sensor members are preferably removable from the container for cleaning of the container.

According to another aspect of the present invention there is provided human body movement monitoring apparatus including the above movement detecting and signalling device, and an indicator unit connectable to the device to receive the generated spacing signal and respond thereto to provide an indication of human body movement.

Preferably, the indicator unit is adapted to be located remote from the sensor members and electrically connected thereto by the connecting member. Preferably, that unit is operable to measure the value of the generated spacing signal and provide an indication of at least the presence and/or absence of movement of the monitored human body based on that measured generated spacing signal value. In that regard, preferably, the unit bases the indication on whether or not the value of the spacing signal is changing; a changing value meaning movement presence whilst an unchanging value meaning movement absence. That indication may be continuous or intermittent and may indicate the extent of any movement or merely the presence or absence of that movement.

Preferably, the indicator unit provides a continuous indication of the presence and absence of movement of the monitored article. In that regard, preferably, the unit receives the generated spacing signal and continuously measures the value of that signal and compares each measured value with an immediately preceding measured value to determine whether or not that value is changing.

Preferably, the indicating unit includes suitable comparator means to measure and compare the generated spacing signal values, and initiate a trigger signal indicative of movement absence when successive measured spacing signal values are unchanged and indicative of movement presence when successive measured spacing signal values change.

That unit comparator means may directly measure and compare the values of the received generated spacing signal. Preferably, however, the unit is responsive to the received generated spacing signal.

to generate a related measuring signal which has a value which is more stable and can be more readily measured and compared by the comparator means.

To that end, preferably, the indicator unit also includes measuring means operable to receive the generated spacing signal and measure the value of that generated signal and generate a measuring signal, as a function related to the measured values of the generated spacing signal, and whose value is measured and compared by the comparator means.

Preferably, the measuring means includes: a frequency generator responsive to a received spacing signal to generate a function related frequency signal; and a frequency-to-voltage converter connected to the frequency generator and responsive to a received frequency signal to generate a function related voltage level signal forming the measuring signal. Preferably, the comparator means includes a voltage comparator operative to receive the voltage level signal from the converter and initiate the trigger signal indicative of movement absence whilst the voltage level in the voltage level signal remains unchanged and initiate the trigger signal indicative of movement presence whilst the voltage level in the voltage level signal is changing.

Preferably, the indicator unit includes indicator means operable to provide a continuous indication of human body movement presence and absence.

To that end, the indicator means preferably includes a pair of indicators connected to the comparator means, to receive the trigger signals therefrom, one of the indicators, which may provide an aural indication, responsive to the received trigger signal indicative of movement absence to become activated and thereby indicate movement absence, and the other one of the indicators, which may provide a visual indication, responsive to the received trigger - signal indicative of movement presence to become activated and thereby indicate movement presence.

Sometimes such as in the example application of the apparatus, there are momentary pauses in the monitored movement which will correctly trigger an indication of the absence of that movement but which need not have triggered that indication because of almost immediate movement resumption.

To alleviate this unnecessary indication initiation of the indication of absence of movement is preferably delayed for a predetermined time lapse. That delay is preferably provided by a suitable time delay means included in the comparator means which delays initiation of the trigger signal indicative of human body movement absence for a predetermined variable time lapse following commencement of an unchanging voltage level in the voltage level signal and cancel initiation of the trigger signal indicative of human body movement absence following recommencement of a changing voltage level within the predetermined time lapse.

The following description refers in more detail to the essential and optional features of the present invention. To facilitate an understanding of that invention, reference is made to the accompanying drawings where these features are illustrated in a preferred embodiment. It is to be understood that the essential and optional features of the invention are not limited to the preferred embodiment of these features as shown in the drawings.

In the drawings: Figure 1 is a perspective view of a human body movement detecting and signalling device according to a preferred embodiment of the present invention; Figure 2 is an enlarged, partial cross-sectional view of the movement detecting and signalling device taken through Section A-A of Figure 1; Figure 3 is a top plan view of one of the sensor members of the movement detecting and signalling device of Figure 1; Figure 4 is an enlarged side elevational view of the sensor sheet taken through Section B-B of Figure 3; and, Figure 5 is a diagrammatic view of the human body movement monitoring apparatus according to a preferred embodiment of the present invention.

Referring to the drawings, where like reference numberals identify like components, and particularly Figures 1 and 2 thereof, there is generally shown human body movement detecting and signalling device 1. That device 1, includes a plurality of juxtaposed sensor members 2, stacked together in an overlying relationship so as to form a pad. Sensor members 2, are grouped together in pairs, each pair comprising sensor sheet 3, and sensor sheet 4.

Sensor members 2, are of identical construction, but in each pair, sensor sheets 3 and 4 are relatively reversed. A typical sensor member 2, illustrated in Figures 3 and 4, is of a generally planar and rectangular configuration. About thirty such sensor members 2, may be provided, and each may measure about 70 mm by 90 mm. Each sensor member 2, has a main body 5, with peripheral edge 6, body 4, being removed as at portion 7. Mounting aperture 8, extends completely through sensor member 2, adjacent peripheral edge 6, and removed portion 7.

Each sensor member 2, is composed from inner electrically conductive lamina 9, sandwiched between outer dielectric laminae 10. Conductive lamina 9, is a sheet of metal foil whilst dielectric laminae 10, are sheets of plastic film applied and adhered to conductive lamina 9, so as to completely coat that conductive lamina 9. In this way, each sensor member 2, is flexible and electrically insulated from each adjacent sensor member 2, when stacked together.

In this preferred embodiment, movement detecting and signalling device 1, also includes elongated fastening member 11, maintaining sensor members 2, in their juxtaposed overlying relationship. Fastening member 11, has generally channel shaped fastening strip 12, consistent with the width of the sensor members 2 and arranged so as to receive therein a region of peripheral edge 6, of each sensor member 2.

Fastening strip 12, has a pair of spaced apart mounting apertures 13 and 14, provided therein, those apertures being arranged so that aperture 13, aligns with the mounting aperture 7, in sensor sheets 3, whilst aperture 14, aligns with mounting aperture 8, in sensor sheets 4, when sensor sheets 3 and 4 are received within fastening strip 12. Fastening strip 12, is composed of electrically nonconducting material, such as plastic, so that sensor members 2, are not electrically interconnected thereby.

Fastening member 11, also has fastening bolts 15,16, extending through aligned mounting apertures 13,14 in fastening strip 12 and mounting apertures 8, in sensor members 2, and bolts 15,16, are maintained in those apertures by fasteing nuts 17 screw-threadably mounted on fastening bolts 15,16 so as to firmly secure sensor members 2, to fastening strip 12. This in turn maintains sensor members 2, in their juxtaposed overlying relationship and sensor sheets 3, and 4, of each pair of sensor members 2, in their relatively reversed orientations, but permits sensor sheets 3 and 4, to move relatively freely toward and away from each other to alter the spacing therebetween.Fastening bolts 15,16, and nuts 17, are composed of electrically conducting material, such as brass, so that they electrically interconnect all of the respective sensor sheets 3, and 4, through whose mounting apertures 8, they extend.

In this preferred embodiment, movement detecting and signalling device 1, further includes connecting member 18, for electrically connecting the sensor members 2, to an electrical power source and an indicator unit, as will be described more fully hereinafter. Connecting member 18, includes a pair of electrical conductors 19,20, conductor 19, being electrically connected to sensor sheets 3, through fastening bolt 15, whilst conductor 20, being electrically connected to sensor sheets 4, through fastening bolt 16. Connecting member 18 also includes an electrical connecting jack 21, for removably connecting conductors 19,20, to the electrical power source and indicator unit.

In this preferred embodiment, sensor members 2, and fastening member 11 may be housed in a protective container (not shown). That container may be in the nature of a removable pouch of flexible and washable fabric material. In this way, that pouch allows ready transmission of movement applied thereto to sensor members 2, and also allows the pouch to be washed and so maintained in a clean condition. That pouch may be constructed so as to facilitate direct or indirect attachment of sensor members 2, to the human body whose movement is to be detected. In that regard, the pouch may be provided with straps for tying the pouch to the human body or may be incorporated into a vest worn by the human body.

Turning now to Figure 5, there is generally shown human body movement monitoring apparatus 22, which includes detecting and signalling device 1, electrically connected through connecting member 18, to indicator unit 23. Apparatus 22, is connectable to an electrical power source through connecting plug 24, so as to supply electrical power to device 1, and indicator unit 23. The electrical power source may be provided by suitable rechargeable or replaceable storage batteries so that monitoring apparatus 22, can be portable, or a main alternating current network suitably rectified prior to delivery to device 1, and indicator unit 23. Connecting plug 24 may include a switch element (not shown) to selectively control supply of power thereto to apparatus 22.

In this preferred embodiment, indicator unit 23, includes measuring means 25, having a frequency generator 26, electrically connected to detecting and signalling device 1, through connecting member 18, to receive an electrical spacing signal from device 1, and generate a function related frequency signal.

Measuring means 25, also has a frequency-tovoltage converter 27, electrically connected to frequency generator 26, so as to receive the frequency signal, generated therefrom. Frequency-to-voltage converter 27, is responsive to that received frequency signal to generate a related voltage level signal forming a measuring signal from measuring means 25.

In this preferred embodiment, indicator unit 23, also includes comparator means 28, operative to receive the voltage level signal from measuring means 25, and initiate a trigger signal at comparator means output 29, indicative of movement absence whilst the voltage level in the voltage level signal from measuring means 25, remains unchanged and to initiate a trigger signal at comparator means output 30, indicative of movement presence whilst the voltage level in the voltage level signal from measuring means 25, is changing. Comparator means 28, has voltage comparator 31 electrically connected to frequency-to-voltage converter 27, so as to receive the voltage level signal generated therefrom and monitor the voltage level thereof to determine whether or not it is changing.A changing voltage level causes voltage comparator 31, to initiate an output signal at voltage comparator outputs 32, and 33, whilst an unchanging voltage level causes no output signal at outputs 32, and 33, of voltage comparator 31. The output signal at voltage comparator output 33, becomes a trigger signal at comparator means output 30.

Comparator means 28, also has time delay unit 34, electrically interconnecting voltage comparator output 32, and comparator means output 29, and is responsive to an output signal from voltage compa rator31,to delay initiation of trigger signal at comparator means output 29, until there is a predetermined time lapse during which no output signal is received by time delay unit 34. In this way indication of momentary human body movement absence is avoided. Time delay unit 34, may be variable so as to vary the predetermined time lapse.

In this preferred embodiment indicator unit 23, further includes indicator means 35, operative to provide an indication to a user of apparatus 22, as to whether or not apparatus 22, is monitoring human body movement. Indicator means 35, provides a continuous indication of human body movement presence and absence being monitored and that is provided by both a visual and aural indication. To that end, indicator means 35, includes indicators 36, and 37, connected respectively to receive the trigger signal from comparator means outputs 29, and 30.

Indicator 36, may be an aural indicator, such as a siren or like alarm, which becomes activated when the trigger signal issues from comparator means output 29, thereby indicating human body movement absence. Indicator 37, may be a visual indicator, such as a light, which becomes activated when the trigger signal issues from comparator means output 30, therebyto indicate human body movement presence.

In this preferred embodiment frequency generator 26, frequency-to-voltage converter 27, voltage comparator 31, and time delay unit 34, of monitoring apparatus 22, are all of suitable electronic construction and arrangement individually well known and appreciated by those persons skilled in the relevant art.

In using monitoring apparatus 22, constructed in accordance with the preferred embodiment as outlined above and in relation to the example application, sensor members 2, of detecting and signalling device 1, are initially attached to an infant whose body movement is to be monitored during sleep.

Sensor members 2, are located on the infant body trunk, such as on the chest or back of the infant so that body movement resulting from breathing is principally monitored. Attachment of sensor members 2, may be facilitated through suitable strapping or a vest as previously detailed.

Connecting member 18, is then fed between the infant's legs and electrically connected to remotely located indicator unit 23.

Indicator unit 23, is connected to an electrical power supply through connecting plug 24, thereby to place apparatus 22, in a monitoring condition. In this condition, a spacing signal as a measure of electrical capacitance between adjacent sensor sheets 3 and 4, is generated by sensor members 2, and transmitted through connecting member 18, to indicator unit 23. In indicator unit 23, that spacing signal is translated by frequency generator 26, into a' related frequency signal which is transmitted to frequency-to-voltage converter 27, for translation into a related voltage level signal. That voltage level signal is transmitted from frequency-to-voltage converter 27 to voltage comparator 31 where successive voltage levels in the voltage level signal are compared.

As the infant's body trunk moves as a result of breathing or otherwise, spacing between adjacent sensor sheets 3 and 4, is caused to alter, thereby altering the value of the spacing signal and so successive voltage levels in the voltage level signal compared by voltage comparator 31. Those chang ing voltage levels causes voltage comparator 31 to initiate an output signal through voltage comparator output 33, to form a trigger signal at comparator means output 30, transmitted to indicator 37, to activate that indicator 37, and so indicate the presence of infant body movement. Voltage comparator 31, also initiates an output signal through voltage comparator output 32, to time delay unit 34, deactivating unit 34, so as not to initiate any trigger signal at comparator means output 29.

Should infant body trunk movement cease, then the voltage levels in the voltage level signals received and compared by voltage comparator 31 remain unchanged and as a result no output signal issues from voltage comparator output 33, and no trigger signal is transmitted to indicator 37 to activate that indicator 37. In addition no output signal is initiated at voltage comparator output 32, causing time delay unit 34 to activate and if maintained activated for a predetermined time lapse, through no receipt of an output signal, will transmit a trigger signal through comparator means output 29 to indicator 36, and thereby activate that indicator 36, so as to indicate body movement absence.

Activation of indicator 36 is a warning to persons minding the infant that infant movement has ceased so that the infant should be immediately checked.

The reverse procedure will remove the infant from apparatus 22, and place that apparatus in a nonmonitoring condition.

A detecting and signalling device according to the present invention has an advantage that it is nondestructive and reusable, and its operation is relatively unaffected by conditions prevailing in the vicinity of the human body whose movement is being detected so that misleading movement detection is alleviated and reliable movement detection and signalling is enhanced.

In addition, both the detecting and signalling device and monitoring apparatus are relatively simple yet effective and reliable in construction and operation. Accordingly, particularly in the example application, the device and apparatus lend themselves toward widespread use by person relatively inexperienced in such devices and apparatus.

Moreover, the costs of purchase and operation may be minimized.

Various other modifications and/or alterations may be made to the detecting device and monitoring apparatus without departing from the ambit of the present invention as defined in the claims appended hereinto.

Claims (20)

1. A human body movement detecting and signalling device, including: a plurality of juxtaposed, relatively movable, electrically conducting sensor members, the sensor members connectable to an electrical power source and operable to generate an electrical spacing signal as a function related to the spacing between adjacent sensor members, construction and arrangement of the device being such that, in use, the sensor members are positioned adjacent a human body and respond to movement of that body by varying the spacing between at least two adjacent sensor members, thereby to alter the generated spacing signal and so signal movement of the human body.

2. A device as claimed in claim 1, wherein the sensor members are adapted to be mounted directly on the human body to move generally in unison therewith.

3. A device as claimed in claim 1 or 2, wherein the sensor members are flexible and substantially freely and readily movable toward and away from each other in response to movement of the human body.

4. A device as claimed in any preceding claim, wherein adjacent ones of the sensor members are electrically insulated from each other and alternate ones of the sensor members are electrically connected to each other, so that the generated spacing signal is a measure of electrical capacitance occurring between adjacent sensor members.

5. A device as claimed in any preceding claim, wherein the sensor members are stacked together in an overlying relationship, and are fastened together along a corresponding peripheral edge region so as to maintain the sensor members in their overlying relationship.

6. A device as claimed in claim 5, and further including an elongated fastening member to which the sensor members are fastened to maintain those sensor members in their juxtaposed overlying relationship.

7. A device as claimed in any preceding claim, wherein each of the sensor members is a sensor sheet, including an inner electrically conductive lamina connectable to the electrical power source, and outer dielectric laminae insulating the conducting lamina of adjacent ones of the sensor members from each other, the generated spacing signal being a measure of electrical capacitance between conductive lamina of adjacent ones of the sensor sheets.

8. A device as claimed in claim 7, wherein each sensor sheet, the conductive lamina is a sheet of metal foil, and the dielectric laminae are a pair of sheets of plastic film applied to respective faces of the metal foil sheet.

9. A device as claimed in any preceding claim, and further including a connecting member for electrically connecting the sensor members to an indicator unit operable to receive the generated spacing signal and respond thereto by providing an indication of human body movement.

10. A device as claimed in any preceding claim, wherein the sensor members are enclosed in a removable container, composed of flexible and waterproof material to allow transmission of article movement therethrough to the sensor members and to maintain the sensor members in a clean condition.

11. A human body movement detecting and signalling device substantially as hereinbefore described with reference to the accompanying drawings.

12. Human body movement monitoring apparatus, including: a movement detecting and signalling device having a plurality of juxtaposed, relatively movable, electrically conducting sensor members, the sensor members connectable to an electrical power source and operable to generate an electrical spacing signal as a function related to the spacing between adjacent sensor members, and the sensor members being adapted to be positioned adjacent a human body and respond to movement of that body by varying the spacing between at least two adjacent sensor members thereby to alter the generated spacing signal and so signal movement of the human body; and, an indicator unit connectable to the detecting and signalling device to receive the generated spacing signal and respond thereto to provide an indication of human body movement.

13. Apparatus as claimed in claim 12, wherein the indicator unit includes: measuring means operable to receive the generated spacing signal and measure the value of that generated signal and generate a measuring signal as a function related to the measured values of the generated spacing signal; and, comparator means operable to receive the measuring signal and measure the value of the measuring signal received and initiate a trigger signal indicative of movement absence when the measuring signal value is unchanging and indicative of movement presence when the measuring signal value is changing.

14. Apparatus as claimed in claim 13, wherein the measuring means includes: a frequency generator responsive to a received spacing signal to generate a function related frequency signal; and a frequency-to-voltage converter connected to the frequency generator and responsive to a received frequency signal to generate a function related voltage level signal forming the measuring signal.

15. Apparatus as claimed in claim 14, wherein the comparator means includes a voltage comparator operative to receive the voltage level signal and initiate the trigger signal indicative of movement absence whilst the voltage level in the voltage level signal remains unchanged and initiate the trigger signal indicative of movement presence whilst the voltage level in the voltage level signal is changing.

16. Apparatus as claimed in claim 15, wherein the comparator means also includes a time delay unit operable to delay initiation of the trigger signal indicative of human body movement absence for a predetermined variable time lapse following com mencementofan unchanging voltage level in the voltage level signal, and cancel initiation of the trigger signal indicative of human body movement absence following recommencement of a changing voltage level within the predetermined time lapse, thereby avoiding indication of momentary movement absence.

17. Apparatus as claimed in any one of claims 12 to 16, wherein the indicator unit includes indicator means operable to provide a continuous indication of human body movement presence and absence.

18. Apparatus as claimed in claim 17, when appended to any one of claims 13 to 16, wherein the indicator means includes a pair of indicators connected to the comparator means to receive the trigger signals therefrom, one of the indicators responsive to the trigger signal indicative of movement absence to become activated and thereby indicate movement absence, and the other one of the indicators responsive to the trigger signal indicative of movement presence to become activated and thereby indicate movement presence.

19. Apparatus as claimed in any one of claims 12 to 18, wherein the movement detecting and signalling device is as claimed in any one of claims 2 to 11.

20. Human body movement monitoring apparatus as hereinbefore described with reference to the accompanying drawings.