AU2010101280A4 - Sensor pad for bed monitor and system - Google Patents

Description

1 SENSOR PAD FOR BED MONITOR AND SYSTEM Field of the Invention The present invention relates to a sensor pad for a bed monitor and, in some embodiments, 5 to a patient monitoring system using the sensor pad. In particular, the invention is intended for use in hospitals, nursing homes and aged care facilities. Background to the Invention The risk of falling from a bed in a hospital, nursing home or aged care environment, 10 compared to a domestic home, is greatly increased. Research shows many factors for this including unfamiliar surroundings and medication. Many falls happen at night when the patient attempts to exit from a bed. Accordingly, detecting a patient leaving a bed is particularly critical in these environments. While a number of detection systems have been used in the past, those systems have drawbacks associated with the unique difficulties of 15 trying to detect genuine "bed-leaving" movement as opposed to simple movement within the bed, i.e. when a patient turns from side to another. Some previous systems used methods of detecting a patient once the bed had been exited, for example, by the use of floor pressure mats. However, such equipment is easily 20 damaged, for example, by hospital equipment rolling or moving over the mat, or during cleaning of the room or ward in which the mat is located. In addition, floor mats are subject to urine damage, making such mats unhygienic and unsightly. Whether damaged or not, laid out flat floor mats can, themselves, become a tripping hazard. Furthermore, these are not a reliable form of early detection. Often full body weight standing on them is 25 required for them to activate, by which time the patient has fully exited the bed. Under bed movement sensors have also been used. These sensors are designed to activate when a patient's feet hang over the side of the bed. The sensors may be activated by interrupting a laser or infra red beam, or activating a motion detector as the patient stands. 30 However, due to the nature of a patient being in bed and the bed being in a hospital-type environment, the sensors may be easily knocked out of alignment, for example by patient lifting machines and other apparatus. In addition, blankets and sheets hanging over the 2 edge of the bed constantly trigger false alarms. Another problem is staff turning off the sensor to work in the vicinity of the sensor but forgetting to re-arm it once their work is finished, leaving the patient unprotected. 5 Further, alternative types of sensors are pressure pads that are situated under the patient to detect movement. However, such above-mattress pressure pads can feel uncomfortable to the patient when felt through the sheets. Further, when a patient tosses and turns, these pads can slip from position causing false alarms. They also have a limited life span and are prone to urine damage. 10 Yet further sensors may be placed under a mattress. These under-mattress pressure pads typically have a pressure switch arrangement in a flexible pad. These rely on an "on"f or "off' switch state and are plugged directly into the nurse call system. While these sensors have some advantages over other previous sensors, they are still prone to failure, and 15 especially false alarms. A further problem with existing sensor systems is the nature of the alarm which is activated. Because these systems are connected to the nurse call system, the nurse or caregiver cannot always know to give priority to a potentially hazardous situation. 20 The sensor of the present invention seeks to overcome or at least ameliorate some of the failings and shortcomings of other devices currently in use in hospitals and the like. Summary of the Invention 25 The present invention provides a sensor pad comprising two spaced apart plate members, a resilient gasket, at least one resilient biasing means and a switch, wherein the gasket and the biasing means bias the plate members apart, and thereby maintain the switch in a first condition. Preferably, the switch is an electrical switch. Optionally, the sensor comprises more than one electrical switch, wherein each electrical switch is independently movable 30 between a first condition and a second condition in response to movement of the plate members. In certain embodiments of the present invention, at least one of the plate members includes a bleed hole therein to allow air to egress slowly from between the plate 3 members when the plate members are urged together, and also to allow the ingress of air when the plate members are urged apart by the biasing means and/or resilient gasket. Preferably, the sensor pad of the present invention is adapted for use under a mattress. 5 The present invention also provides a patient detection system comprising a sensor pad according to the present invention and a monitoring device, wherein the monitoring device detects the switch moving between the first and second conditions. Preferably, the monitoring device is configured to send an alarm signal to a nurse call system. More preferably, the monitoring device optionally includes a night light activator. 10 Brief Description of the Figures Figure 1 shows a cross-section of a sensor pad according to one embodiment of the present invention. 15 Figure 2 shows a plan view of a sensor pad according to different embodiments of the present invention, comprising one switch (2A), two switches (2B) and a strip switch (2C). Figure 3 shows an embodiment of a monitoring device according to the present invention. 20 Figure 4 shows a mounting side of the monitoring device illustrated in Figure 3, as well as the dovetail mounting plate. Figure 5 shows a view of the display side of the monitoring device illustrated in Figure 3. 25 Figure 6 shows an embodiment of a typical set up of a patient monitoring system according to the present invention. Detailed Description of the Invention The risk of falling from a bed in a hospital, nursing home or aged care environment 30 compared to a domestic home is greatly increased. Research shows many factors for this including unfamiliar surroundings and medication. Many falls happen at night when the 4 patient is attempting to exit a bed. Accordingly, a simple and reliable system is required to alert nursing staff that a patient is trying/intending to exit a bed. A system that meets these requirements needs to: 5 (i) accurately detect the patient exiting the bed; and (ii) reliably alert nursing staff to the situation. In order to accurately detect the patient exiting the bed, the present invention provides an under-mattress a sensor pad, preferably an under-mattress sensor pad. The sensor pad 10 comprises two opposed, spaced apart plate members cooperating with a resilient gasket which spaces the plate members apart and which extends substantially around a periphery of the two plate members to define an void within the sensor pad, the sensor pad further comprises at least one resilient biasing means located within the void and between the plate members. The resilient gasket and resilient biasing means cooperate to maintain the plate 15 members in a spaced apart condition. The under-mattress sensor pad further includes at least one electrical switch, wherein when the plate members are in a spaced apart condition each switch is in a first condition. When a suitable compressive force is applied to the sensor pad, the plate members are moved closer to each other towards a compressed condition. When the plate members move towards the compressed condition, one or more 20 of the switches is moved to a second condition. When the compressive force is reduced or removed, the plate members move towards the spaced apart condition due to the resilient gasket and resilient biasing means. Such change of condition also changes the condition of the switch back to the first condition. 25 When one switch is present, it is preferably substantially centrally located within the sensor pad. When more than switch is present, they may be distributed substantially evenly within the sensor pad. When more than one switch is present, the switches act independently in that they can 30 independently move between the first and the second conditions. Preferably, the switches are connected such when any one or more switches are in the second condition, a signal is 5 sent. In particular, the switches are connected such that each switch does not send an independent signal. The sensor pad in accordance with this invention uses two plate members. Preferably, at 5 least one of the plate members is semi-rigid, wherein in use, the semi-rigid plate may flex, thereby facilitating activation of the switch or switches. Each plate member may be constructed of the same or different materials. In some embodiments of the present invention, the plates may be constructed from any suitable plastic. In certain embodiments of the present invention, the plate members may be substantially rectangular. The overall 10 size of the sensor pad should be sufficient to be able to detect a body lying on a mattress, wherein the mattress is above the sensor pad. For example, a sensor pad having dimensions of approximately 200mm to 650mm wide by 400mm to 900mm long would be suitable, although other sizes could also be suitable. In particularly preferred embodiments of the present invention, the sensor pad has dimensions of 250mm by 450mm, or 300mm by 15 710mm, or 600mm by 710mm. In yet further embodiments, the plate members may be substantially circular, having a diameter of approximately 300mm to 800mm. In sensor pads having dimensions such as 300mm by 710mm, or 600mm by 710mm, it is preferred that there are at least two switches to provide greater sensitivity to the sensor pad 20 and its ability to detect movement close to the edge of the bed. The at least two switches are preferably wired in parallel so that the same electrical signal is generated whether one, or more than one, switch is activated. Accordingly, each switch does not send an independent signal. In yet further embodiments of the present invention, a strip switch, as described in further detail below, may replace one or more of the switches. Thus, as used 25 herein, the phrase "at least two switches" is intended to encompass embodiments having at least one strip switch. The sensor pad should be of sufficient depth for there to be a large enough void to regulate the speed at which the plates approach each other, and to house the switch. However, the 30 depth must not be so great that it presents an uncomfortable lump under the mattress. In some embodiments of the present invention, the overall depth of the sensor pad is between 15mm and 50mm, most preferably approximately 20mm.

6 The plate members are preferably substantially of equal size and shape, and are held and spaced directly horizontally opposite each other by means of a resilient gasket around a periphery of the two plate members. Preferably, the resilient gasket is substantially 5 air-tight. The gasket is positioned between the plate members and at least partially surrounds the periphery of the plate members. The gasket thereby creates a void between the two plate members. The outside edge of the gasket preferably provides a non-slip edging to the surface to the sensor pad. In some embodiments of the present invention, the gasket may be a rubber gasket or seal. 10 In some embodiments of the present invention, the sensor pad includes an air-transfer means by which air may escape from the void defined by the plate members and the gasket. Similarly, the air-transfer means may also allow air to enter the void, from outside the sensor pad. For example, in some embodiments of the present invention, the 15 air-transfer means may comprise a small hole located in at least one of the plate members. In yet further embodiments, the air-transfer means may comprise a valve or gap located in the gasket, or a plate member being composed of a porous material. When a patient lies on the mattress, under which a sensor pad of the present invention is 20 located, each or at least one plate member is urged towards the other under a compressive force. The gasket, being resilient, allows the plate members to approach each other and thereby placing the switch in the second condition. As the gasket is squeezed by the application of weight upon the sensor pad, the plate/s approach each other, and there is a reduction in the volume of the void between the plates. The air-transfer means limits the 25 rate at which air can escape from the void within the sensor pad, thereby causing a time delay before the plates are urged towards each other under the pressure of a patient's weight. In certain embodiments of the present invention, the air-transfer means is a substantially circular hole having a diameter of approximately Imm to 3mm. 30 In certain embodiments of the present invention, there is mounted between the plates, in the void, a resilient biasing means, such as, but not limited to, a spring arrangement. The 7 resilient biasing means slightly forces apart the plates when little or no outside pressure is applied to the sensor pad, thereby maintaining the sensor pad in its spaced apart condition. Preferably, the resilient biasing means and the gasket together apply sufficient force to the 5 plates to keep them apart under the weight of a mattress. However, the additional weight of a body on the mattress is sufficient to at least partly compress the sensor pad. In yet further embodiments of the present invention, there is mounted between the plates, in the void, a plurality of resilient biasing means, such as, but not limited to, spring 10 arrangements. The resilient biasing means slightly forces apart the plates when little or no outside pressure is applied to the sensor pad, thereby maintaining the sensor pad in its spaced apart condition. In some of these embodiments, there is sufficient resilience in the plurality of biasing means that there is no need for the gasket to provide any resilience, in such embodiments the gasket is there simply to define the void in cooperation with the 15 plate members. Positioned within the void is at least one switch. Each switch may comprise one or more components, wherein preferably, at least one component is attached to one of the plates, and another component, if present, may be attached to the other plate, such that when the 20 plates are urged towards each other from the spaced apart condition into the compressed condition, for example, the switch may be toggled between the first and second conditions, for example from on to off, or from off to on, In which case, the switch alters a circuit, preferably an electrical or pneumatic circuit and such alteration is indicative of the change of condition of the sensor pad. Several types of sensors or switches may be used for this 25 application. Pressure switches, micro-switches, piezoelectric switches, accelerometers, switch blade contacts and capacitance switches are known switch arrangements in the art of medical and monitoring devices and are all possible options for a switch for use in the present invention. Alternative types of switches are also envisaged and the preceding list is not intended to be exhaustive. 30 In a preferred embodiment of the present invention, the switch is in the form of a piezoelectric switch. In such an embodiment, the switch is attached to one of the plate 8 members and directly opposite on the other plate member, is positioned a rubber stopper or some other soft resilient material. When the plate members are moved, the rubber stopper, or the like, applies pressure to the piezoelectric switch, thereby creating a current that can be detected by the monitoring device. In embodiments having more than one switch (see 5 Figure 2B), each of the switches may be of the type and arrangement described above. In a further embodiment of the present invention, the switch may be in the form of a piezoelectric strip and may be used to replace a plurality of individual switches (see Figure 2C), Similar to the arrangement described immediately above, the strip switch is attached 10 to one of the plate members and directly opposite on the other plate member, is positioned one or more, preferably two, rubber stoppers or some other soft resilient material. Pressure applied to the strip by any one of the rubber stoppers, or the like, creates a current that can be detected by the monitoring device. 15 The switch is in communication with a monitoring device. Such communication may be wired or wireless. In embodiments of the present invention employing wireless communication, the sensor pad may further comprise a suitable wireless transmitter. In such cases, the wireless signal from the sensor pad may be received by a suitably equipped monitoring device. Alternatively, the nurse call system may receive the signal directly 20 from the sensor pad. In this case, the nurse call system would need to be suitably configured to sound an alarm only under conditions as discussed in detail below. With the sensor pad installed under a mattress, the void between the plates is substantially at its maximum volume, the resilient gasket is in its normal state, and the switch is set to a 25 first condition to indicate that the sensor pad is in the spaced apart condition. When a body weight is applied to the mattress one or both plate members of the sensor pad start to move toward the other. The compression of the sensor pad is delayed by the air escaping through the air-transfer means until the switch is moved to a second condition to indicate that the sensor pad is in the compressed condition. This changed signal is detected by the 30 monitoring device. Due to the plate members being in closer proximity to one another, the volume of air remaining in the void is less than when the sensor pad is in the spaced apart condition.

9 When a person sits up in bed or attempts to exit the bed the switch moves from the second condition to the first condition, because of the plates being urged apart by the biasing means and the gasket. However, the progress of the sensor pad returning to the spaced 5 apart condition is delayed by the rate at which air can be sucked or drawn back into the void which had an earlier enforced reduced air volume. This delay in separation of the plates allows more tolerance to somebody rolling over in bed or normal bed movements therefore not triggering an alarm at every toss and turn of the patient. The delay in compression of the plates allows for the switch to change condition only if a steady body 10 weight is upon the sensor pad. Thereby, someone making the bed or pushing down on the mattress in short bursts will not move the switch to the second condition, however somebody resting in bed will achieve the desired result of sensing a patients presence in a lying down position with great accuracy. 15 In order to reliably alert nursing staff, the sensor pad of the present invention may be used in conjunction with a monitoring device. As noted above, the sensor pad may be connected by hoses, wires or wirelessly to the monitoring device. The monitoring device is in turn capable of sending a signal through an existing nurse call system. In preferred embodiments of the present invention, the monitoring device may be capable of sending a 20 distinguishing signal through the nurse call system so that nursing staff are able to readily distinguish an alarm generated by the monitoring device from other standard signals and alarms that may be used by the nurse call system. In certain embodiments of the present invention, the monitoring device may include or 25 control a night light, such that the night light will illuminate a selected region of the floor where the patient is likely to exit the bed; thereby helping to reduce the risk of injury should the patient be able to exit the bed prior to nursing staff arriving. The monitoring device may also include a means by which various records may be kept, such as, but not limited to, alarm time and staff attendance time. 30 10 The monitoring device in accordance with this invention may be made from any suitable material, preferably a plastic material, such as, but not limited to vac-formed or injection moulded plastic. 5 In specific embodiments of the present invention, the monitoring device may be bed- or wall-mounted. Further, the monitoring device may be shaped to overcome problems found in other bed mounted devices. For example, a bed-mounted monitoring device may be designed to be attached to the back of the bed head and have tapered sides, so as to not get caught on other room furniture when the bed is moved. The bottom of the monitoring 10 device may be tapered so as to reduce the likelihood of damage if the bed is raised or lowered in close proximity to other furniture or equipment. In addition, it is desirable that cables or leads attach to, or pass through, the base of the monitoring device so that, if they are pulled, they can readily disengage with the 15 monitoring device, thereby preventing damage to the monitoring device and/or cables. Preferably, the base of the monitoring device is recessed so as to avoid pinching any leads exiting the monitoring device, if the monitoring device contacts equipment or furniture when the bed is lowered. In further embodiments of the present invention, the nurse call and power cables exiting the base of the monitoring device preferably include inline 20 pull-apart connectors. If the bed is pulled out too far from the wall, such as for cleaning etc., the cables will pull apart without damage being caused. The monitoring device may be mounted by means of a dove tail arrangement wherein a substantially trapezoid mounting bracket is mounted on the mounting surface (wall or bed) 25 with its short parallel side uppermost. The monitoring device includes a corresponding shaped recess on its back allowing the monitoring device to slip on and off its mounting bracket. Recessed behind the dove tail may be setting switches, designed to be hidden from tampering, when the monitoring device is positioned over the dove tail. 30 In preferred embodiments of the present invention, the monitoring device has a display screen to display bed status and record-keeping data. In further embodiments, text displayed on the screen may be reversed in order to display information the correct way up, 11 depending on the orientation of the monitoring device. Such reversal may be achieved by the use of a switch. The monitoring device of the present invention is intended to be in communication, either 5 directly or indirectly, with the bed pad sensor switch via means of a hose, cable/wire or wireless system. The toggling of on/off signals from the switch within the sensor pad are passed through an electronic logic processor arrangement, the settings for which may be readily adjustable making many different modes and features possible. 10 In certain embodiments of the present invention, bed exit alarm delays may be adjusted from, for example, five seconds to fifteen minutes. Another optional setting may be a toilet mode option, which if selected, will illuminate a night light for a predetermined time interval, until the return of the patient to bed. If the patient does not return to bed within a predetermined time the monitoring device will alarm. In addition, the user may select the 15 type of signal being sent to an existing nurse call varying from a pulsed signal, solid on signal, momentary on signal, momentary off signal. The monitoring device in accordance with this invention may be capable of storing bed exit times and/or caregiver response times and/or time periods for which the monitoring 20 device has been switched on and in use. In a further embodiment of the present invention, the monitoring device may include a backup battery mode which activates when the monitoring device recognizes the system is unplugged. It is preferable that the monitoring device indicates when this mode is 25 activated. This may be achieved via an alarm as discussed above, or by an indication on a LCD screen, such as by glowing red and/or giving an audible beep for thirty seconds alerting the caregiver to plug the system in or switch it on. In the event of a power failure the system may be set up to work on battery backup as normal and to use the internal alarm if the bed is exited. The times that the system is switched on and in use are preferably 30 recorded. Falls causing injury within a nursing home or hospital are required to be documented but many incidents happen at night with minimal night duty staff in 12 attendance and no witnesses. The recording of bed exit times and nurse response times ensure that a high duty of care of staff is adhered to and can be proven. The present invention provides a patient detection system including a sensor pad and a 5 monitoring device as hereinbefore described. The system is able to detect the presence or absence of a patient within a bed and alert a nurse or caregiver when a patient attempts to exit or exits a bed. In particular embodiments of the present invention, the system includes a night light. The 10 night light may be incorporated into the monitoring device or linked to the control, preferably via a cable. Preferably, the light is mounted to the underside of the bed by any fixing means known in the art, including, but not limited to, a magnetic strip, Velcro or double sided tape. The system may be configured to illuminate the night light when the bed is exited and simultaneously activate the nurse call or alarm. The light may be turned off 15 by the caregiver, and may share the same switch as the alarm reset switch, when the patient is attended to. Thus, in accordance with this aspect of the present invention, a typical patient detection system comprises: 20 1 an under-mattress sensor pad comprising two substantially rigid plates and a resilient gasket defining an void therebetween, and a switch; and 2. a monitoring device, preferably with an LCD screen for information display and data collection 25 Detailed description of the Figures The present invention will be described with reference to the accompanying Figures, wherein like reference numerals designate like or corresponding parts throughout the several views. The illustrated embodiments are intended only as examples of the present 30 invention and are in no way intended to limit the scope of the invention described herein.

13 Figure 1 shows a cut away side projection of an embodiment of a sensor pad 100 according to the present invention. The resilient gasket 110 has a top 111 and bottom 112 groove into which the top 121 and bottom 122 plate members are inserted and held in place. The gasket 110 has a void 113 within, making it collapsible when pressure is applied thereto by 5 bringing the two plate members 121,122 together, enabling the switch 130 components to come into contact. The use of one or more biasing means 140 adjacent the switch 130 for urging the two plate members 121,122 apart have proven beneficial. The air-transfer means 125 is key to the sensor's reliable function causing a delay in compression and expansion of the sensor 100 by limiting the rate at which air is able to enter or exit the void 150 10 defined by the two plates 121,122 and by the gasket 110. Figure 2 shows plan views of sensor pads 100 incorporating different switch arrangements. Figure 2A shows the embodiment illustrated in Figure 1, having a single, centrally positioned switch 130, Figure 2B shows an embodiment having two equally distributed 15 switches 130; and Figure 2C shows an embodiment having a single strip switch 131 positioned substantially centrally within the sensor pad. These embodiments are wired examples and thus have a cable 190 with a plug 195 on the end, which cable 190 is also connected to the or each switch 130 or 131. Part of the gasket 110 is illustrated as covering the periphery of the upper plate 121, thereby providing a non-slip region to the sensor pad. 20 Figure 3 shows a monitoring device 200 according to one embodiment of the present invention. The function of the monitoring device 200 is to contain the necessary electronic components and logic board and display, and to link the sensor pad 100 to an alarm system. The monitoring device 200 is in direct communication with the sensor pad 100, in 25 this embodiment, by means of a cable 190 and reads the switching status of the sensor pad 100 to determine whether someone is present or not within the bed and alarming as necessary. In the illustrated embodiment, the cables exiting the bottom of the monitoring device are for connection to an auxiliary night light cable 232A, the sensor pad cable 190A and power/nurse call cable 210A, all have pull apart in line plugs to avoid cord damage if 30 stretched. The monitoring device 200 is able to recognize if any cord has become unplugged and in turn will emit an audio beep while signalling the malfunction on a display screen. This said feature is included to alert caregivers to the non-functioning of 14 the patient detection system due to cables becoming disconnected during, for example, room cleaning and/or bed moving. Furthermore, as illustrated, the cables exiting the base of the monitoring device 200 may be recessed into a cavity 240. The cavity 240 further protects the wiring from damage if the bed and attached monitoring device 200 are lowered 5 onto other equipment. The bottom edge 250 of the monitoring device 200 may be tapered to avoid catching other equipment. Similarly, the sides 260 of the monitoring device 200 may be tapered to avoid catching other equipment. Figure 4 shows the rear view of a monitoring device 200 which is preferably used with the 10 present invention, as well as a means for mounting the monitoring device 200 via a dove tail arrangement, A dovetail plate 290 is fixed to a wall or bed, by any suitable temporary or permanent means. The dovetail plate 290 has tapered edges 295 onto which the similarly tapered edge 285 of the monitoring device 200 can be slid. Under the dovetail arrangement are function switches 270. These switches are for setting changes and 15 accessing information stored within the memory of the monitoring device 200. The position of the function switches 270 means that the monitoring device 200 must be lifted off the dovetail plate 290 in order to be accessed. Hiding the function switches 270 in this way means that patients are less likely to interfere with the switches 270 and the function of the monitoring device 200 will not be affected. This is of particular importance when the 20 invention is used with dementia patients who may otherwise fiddle with and/or change settings on more obvious controls. Figure 5 shows the top view of the monitoring device 200 for use with the present invention with an LCD screen 280 and on/off reset button 205. The LCD screen 280 may 25 have a reversible flip screen mode depending on whether the monitoring device 200 is bed or wall mounted. The LCD screen 280 may have three different colours with which it can be backlit depending on the status of the system. Figure 6 shows an exemplary embodiment of a patient detection system according to the 30 present invention and its typical positioning when in use. The mattress is not shown to improve clarity of the illustration. The sensor pad 100 is strategically positioned to be under the patient's upper back region when lying in bed 300. In a typical arrangement, a 15 mattress would be positioned over the sensor pad 100, The sensor pad 100 is not prone to movement or damage as it is held into position by the weight of the mattress and by the non-slip edges of the gasket 110 as illustrated in Figure 2 and discussed above, In this embodiment, the sensor pad 100 is in direct communication via means of a cable 190 to the 5 monitoring device 200- The monitoring device 200 in this illustration is mounted behind the bed head 310. In an alternative arrangement the monitoring device 200 may be mounted to a nearby wall. The monitoring device 200 is shown with an optional nurse call cable 210 one end plugged into the monitoring device 200, the other end plugged into the nurse call socket 215. If a standard call bell is already occupying the nurse call socket 215, 10 a double plug may be provided. The monitoring device is also connected to a mains power socket 220. An optional night light 230 is positioned on the under side of the bed 300 and is wired into direct communication to the monitoring device 200 by means of a cable 232. The present invention is not to be limited in scope by the specific embodiments described 15 herein, which are intended as single illustrations of individual aspects of the invention, and functionally equivalent methods and components are within the scope of the invention. Indeed, various modifications of the invention, in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description and accompanying drawings. An embodiment of the functioning of an exemplary patient 20 detection system according to the present invention is described below. Upon turning on the system via a switch 205 on the control unit 200, the LCD screen 280 glows red while the system checks for correct connection of power, nurse call system and sensor pad. 25 If the check is not completed correctly the LCD screen 280 remains red and indicates which component of the system is not correctly connected, by for example a worded or illustrative message on the LCD screen 280. Further, if no power is detected, the monitoring device 200 may emit an alarm since the lack of power may be due to 30 disconnection of the power cable or a power failure. After 30 seconds of no power the monitoring device 200 stops emitting an alarm and the LCD screen 280 remains red. However, the monitoring device 200 must keep functioning, it is therefore envisaged that 16 the monitoring device includes a battery back-up. Further, in the event of a power failure, the monitoring device 200 must be capable of emitting any necessary alarms using an internal alarm, such as a piezo-type pulsing buzz. 5 If the nurse call plug 215 is not detected, the monitoring device 200 may emit an alarm. After 30 seconds, the monitoring device 200 stops emitting an alarm and the LCD screen 280 remains red. Since there is no connection to the nurse call system, the monitoring device 200 must be capable of emitting any necessary alarms using an internal alarm, such as a piezo-type pulsing buzz. 10 If the sensor pad 100 is not detected, the monitoring device 200 must emit an alarm. The monitoring device 200 must not stop emitting the alarm until the sensor pad is connected, since the patient detection system will not function without the sensor pad 100. Optionally, the LCD screen 280 remains red until the sensor pad 100 is connected. 15 Once the check is completed correctly, the LCD screen 280 changes colour to blue to indicate that the system is in standby mode. In this mode, the monitoring device 200 is seeking to detect a person lying in bed. Depending on the type of switch 130 being used, it is possible for the monitoring device to detect a person's pulse and/or respiratory 20 movement as an indication of the person being in bed. For example, a piezoelectric switch can have sufficient sensitivity to detect minor movements. A piezoelectric switch or sensor generally comprises a piece of a ceramic material which, when placed under stress, is capable of generating a current. In the present invention, a piezoelectric switch may be used by attaching the switch on one of the plate members and having directly opposite, a 25 rubber stopper or some other soft resilient material. When the plate members are moved, the rubber stopper, or the like, applies pressure to the piezoelectric switch, thereby creating a current which can be detected by the monitoring device. When the bed is exited there is no pressure applied to the piezoelectric switch and consequently a reduction in the current generated, which change can also be detected by the monitoring device. Due to the 30 sensitivity of piezoelectric materials, slight movements can cause detectable current to be generated. Accordingly, breathing, and even heartbeats, can be detected by some piezoelectric switches. Once a person has been detected, such as by pulse and/or 17 respiratory movement or constant compression of the sensor pad, such as by a resting or sleeping person, the system becomes "armed". In the armed state the LCD screen 280 may change colour to green. The system will not enter an armed state from the standby mode if the monitoring device 200 detects movement, such as the bed being made, or a person 5 getting into bed. If the person sits up in bed, the monitoring device 200 recognizes a lack of pulse and/or respiratory movement or a change in the electrical output of the sensor pad 100 and the system re-enters standby mode. If the person lies back down again within a predetermined 10 time, the system returns to the armed state. If however, the predetermined time elapses an alarm signal is emitted by the monitoring device 200 and/or via the nurse call system. The LCD screen 280 prompts the nursing staff or the caregiver to cancel the alarm by a suitable message displayed upon the LCD screen 280. 15 After an alarm event, it is necessary for nursing staff or the caregiver to reset the system and cancel the alarm. These events are logged in the system for recordal of events that may affect the patient's wellbeing. If the alarm is cancelled but the system is not reset, the system will search again for a heart beat or pulse. If found, the system will then return to the armed state and will log the event as an uncancelled call. 20 Whenever a range is given in the specification, for example, a time range, or a size range, all intermediate ranges and subranges, as well as all individual values included in the ranges given are intended to be included in the disclosure. It will be understood that any 25 subranges or individual values in a range or subrange that are included in the description herein can be excluded from the claims herein. As used herein, "comprising" is synonymous with "including," "containing," or "characterized by," and is inclusive or open-ended and does not exclude additional, 30 unrecited elements or method steps. As used herein, "consisting of' excludes any element, step, or ingredient not specified in the claim element. As used herein, "consisting essentially of' does not exclude materials or steps that do not materially affect the basic 18 and novel characteristics of the claim. The broad term "comprising" is intended to encompass the narrower "consisting essentially of' and the even narrower "consisting of " Thus, in any recitation herein of a phrase "comprising one or more claim element" (e.g., "comprising A"), the phrase is intended to encompass the narrower, for example, 5 "consisting essentially of A" and "consisting of A." Thus, the broader word "comprising" is intended to provide specific support in each use herein for either "consisting essentially of' or "consisting of" The invention illustratively described herein suitably may be practiced in the absence of any element or elements, limitation or limitations which is not specifically disclosed herein. 10 Any prior art reference or statement provided in the specification is not to be taken as an admission that such art constitutes, or is to be understood as constituting, part of the common general knowledge in Australia.

Claims (5)

1. A sensor pad comprising two spaced apart plate members, a resilient gasket, at least one resilient biasing means and at least one switch, wherein the resilient gasket and the biasing means bias the plate members apart and thereby maintain the switch in a first 5 condition.

2. The sensor pad of claim I wherein each switch is independently selected from a group consisting of: pressure switch, micro switch, piezoelectric switch, piezoelectric strip switch, accelerometer, 10 switch blade contact, and capacitance switch.

3. The sensor pad of claims 1 to 2 wherein the sensor pad is air tight and adapted for use under a mattress. 15

4. The sensor pad in any claims I to 3 wherein at least one of the plate members includes a bleed hole to allow air to egress slowly from between the plate members when the plate members are urged together, and/or to allow the ingress of air when the plate members are urged apart by the biasing means and/or the resilient 20 gasket.

5. A patient detection system comprising a sensor pad according to any one of the preceding claims and a monitoring device, wherein the monitoring device is configured to self arm and/or send an alarm signal to a nurse call system.