Patent Publication Number: US-10762753-B2

Title: Methods and systems for determining the time at which a seal was broken

Description:
BACKGROUND 
     Field of the Disclosure 
     The present subject matter relates to systems and techniques for determining when a seal on a container or the like was broken. More particularly, the present subject matter relates to the use of an environmentally sensitive material to determine when a seal on a container or the like was broken. 
     Description of Related Art 
     It is common to keep employ a sealed container or environment for any of a number of applications. For example, medication is frequently provided in a sealed container, such as a blister pack, which may have a number of individual sealed cells that must be broken to access a dose of medication. It may be advantageous to be able to determine when the seal on a cell was broken, for example, a subject may be under the orders of a doctor or medical care provider to ingest a dose of medication at a particular time. If the subject is not within a facility under the control of the doctor or medical care provider (e.g., a hospital or nursing home), it may be difficult for the doctor or medical care provider to know whether the subject has ingested the medication at the proper time. Accordingly, in this case, it would be advantageous to provide systems and methods that may be used to determine when a particular seal was broken. 
     SUMMARY 
     There are several aspects of the present subject matter which may be embodied separately or together in the devices and systems described and claimed below. These aspects may be employed alone or in combination with other aspects of the subject matter described herein, and the description of these aspects together is not intended to preclude the use of these aspects separately or the claiming of such aspects separately or in different combinations as may be set forth in the claims appended hereto. 
     In one aspect, a system for determining when a seal of a sealed container was broken includes a sealed container and an electrical circuit. The sealed container includes a seal that separates the interior of the container from the outside environment. An environmentally sensitive conductor of the circuit is positioned within the interior of the sealed container. The conductor has an electrical property with a known initial value that changes in a predictable manner as a function of time and exposure to the outside environment. After the seal has been broken, a present value of the electrical property may be used to determine the time at which the seal was broken and the conductor was exposed to the outside environment. 
     In another aspect, a system for determining when a seal of a sealed container was broken includes a sealed container and an electrical circuit. The sealed container includes a seal that separates the interior of the container from the outside environment. An environmentally stable conductor and an environmentally sensitive conductor of the circuit are positioned within the interior of the sealed container. The environmentally sensitive conductor has an electrical property with a known initial value that changes in a predictable manner as a function of time and exposure to the outside environment. After the seal has been broken, a present value of the electrical property may be used to determine the time at which the seal was broken and the environmentally sensitive conductor was exposed to the outside environment. 
     In yet another aspect, a method of determining when a seal of a sealed container was broken includes providing a sealed container having a seal that separates an environmentally sensitive conductor positioned within an interior of the container from an outside environment. The conductor has an electrical property with a known initial value that changes in a predictable manner as a function of time and exposure to the outside environment. The seal is broken, thereby exposing the conductor to the outside environment and allowing the value of the electrical property to change. The time at which the seal was broken is then determined based on the present value and the initial value of the electrical property. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic view of an electrical circuit having an environmentally stable conductor and an environmentally sensitive conductor for determining the time at which a seal was broken according to an aspect of the present disclosure; 
         FIG. 2  is a diagrammatic view of the circuit of  FIG. 1 , with the environmentally stable conductor being incorporated into the seal of a sealed container or package; 
         FIG. 3  is a graph illustrating the resistance of the circuit of  FIG. 1  before and after the environmentally stable conductor and seal are broken; 
         FIG. 4  is a diagrammatic view of the circuit of  FIG. 1 , with an associated input/output port for determining the resistance of the environmentally sensitive conductor; 
         FIG. 5  is a diagrammatic view of the circuit of  FIG. 1 , with an associated analog-to-digital converter for determining the resistance of the environmentally sensitive conductor; 
         FIG. 6  is a graph of the change in voltage over time for the circuit of  FIG. 4 ; 
         FIG. 7  is a plan view of a medication-containing cell of a medical container incorporating the circuit of  FIG. 1  for determining when a seal on the cell was broken; 
         FIG. 8  is a perspective view of two portions of a container, with an environmentally stable conductor associated with both portions and an environmentally sensitive conductor associated with one portion for determining when the container was opened; 
         FIG. 9  is a diagrammatic view of an electrical circuit having a single, environmentally sensitive conductor for determining the time at which a seal was broken according to an aspect of the present disclosure; and 
         FIG. 10  is a plan view of a medication-containing cell of a medical container incorporating the circuit of  FIG. 9  for determining when a seal on the cell was broken. 
     
    
    
     DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriate manner. 
     According to an aspect of the present disclosure, a system for determining when a seal of a sealed container or package or the like is broken may include a circuit  10  of the type shown in  FIG. 1 .  FIG. 2  illustrates the circuit  10  as positioned within the interior of a sealed container  12 , behind a seal  14 , as will be described in greater detail herein. 
     The circuit  10  of  FIGS. 1 and 2  includes two conductors  16  and  18  that are electrically connected and positioned within a sealed environment or container  12 . In the illustrated embodiment, the conductors  16  and  18  are connected in parallel, but other circuit configurations may also be employed without departing from the scope of the present disclosure. The first conductor  16  is generally environmentally stable, such that at least one electrical property of the first conductor  16  remains generally uniform before and after being exposed to the environment outside of the sealed container  12 . The second conductor  18  is environmentally sensitive, such that at least one electrical property of the second conductor  18  will change as a function of time after being exposed to the environment outside of the sealed container  12 . 
     In one embodiment, the first and second conductors  16  and  18  are resistors, with the first conductor  16  having a resistance that remains generally uniform before and after being exposed to the environment outside of the sealed container  12 . As for the second conductor  18 , it has a resistance that changes as a function of time after being exposed to the environment outside of the sealed container  12 . The second conductor  18  may be sensitive to any one or more environmental factors. For example, the second conductor  18  may be configured to react to a liquid or gas in the outside environment by corroding to some degree in order to change its resistance. A second conductor  18  formed of a conductive metal may at least partially convert to an oxide or other non-conducting compound as a mechanism for changing its resistance. An organic conductor (e.g., polyaniline) may have its structure attacked as a mechanism for changing its resistance. Hence, depending on the nature of the outside environment to which the second conductor  18  is to be exposed, a particular material may be selected for the second conductor  18  to elicit a desirable reaction and predictable resistance change. 
     While, in one embodiment, the conductors  16  and  18  are provided as resistors (and the discussion which follows refers to resistance as the variable electrical property of the second conductor  18 ), it should be understood that the conductors may be other electrical components. For example, the conductors  16  and  18  may be capacitors (e.g., a second conductor  18  comprising a capacitor with a wet dielectric layer that dries out over time when exposed to the outside environment) or inductors or transistors or diodes, provided that one of the conductors has an electrical property that is variable in a predictable manner in the presence of certain environmental conditions. In another embodiment, the second conductor  18  may be a battery, such as a zinc-air battery, which only produces a voltage when it is exposed to the atmosphere. In such an embodiment, if a current is being drawn by the associated circuit  10 , then the voltage of the second conductor/battery  18  will decrease over time in a predictable manner. If conductors other than resistors are used and a variable electrical property other than resistance is monitored (e.g., capacitance or inductance), it may be advantageous for the electrical circuit to be differently configured than as shown in  FIGS. 1 and 2 . 
     If the two conductors  16  and  18  are provided as resistors, placing them in parallel renders the resistance between points A and B equal to a combination of the resistance of the conductors  16  and  18 . In particular, the total resistance R 0  is equal to the product of the two resistances divided by the sum of the two resistances.  FIG. 3  shows how the resistance between points A and B changes as a result of the seal  14  and the first conductor  16  being broken at time T. Before the seal  14  is broken, both conductors  16  and  18  are intact and contributing to the resistance between points A and B, resulting in a resistance of R 0 . 
     When the seal  14  and first conductor  16  are broken at time T, the resistance of the first conductor  16  essentially becomes infinite (i.e., an open circuit), as no current will flow therethrough. At that time, all of the current between points A and B will flow through the second conductor  18 , such that the resistance between points A and B instantaneously becomes the resistance R 2  of the second conductor  18 . This is illustrated in  FIG. 3  with a stepwise transition from R 0  to R 2  at time T when the seal  14  and first conductor  16  are broken. For some embodiments, it may be advantageous for the resistance of the first conductor  16  to be much less than the resistance of the second conductor  18  to create a larger step at time T, which may be easier to detect by a monitoring device. In other embodiments the two conductors  16  and  18  may be different circuit components, provided that the second conductor  18  has a time- and environmentally variable electrical property and the first conductor  16  is configured to allow for immediate open/closed detection (which allows an associated monitoring system to see the varying electrical property of the second conductor  18  when the seal  14  has been broken). 
       FIG. 2  illustrates an exemplary system configuration which ensures that the first conductor  16  is broken at the same time as the associated seal  14 . In the system of  FIG. 2 , the circuit  10  (which includes the first and second conductors  16  and  18 ) is mounted within a sealed container or package or the like  12  that is separated from the outside environment by a seal or barrier or frame  14 . In addition to protecting the environmentally sensitive second conductor  18  from the outside environment, the seal  14  may additionally be an insulative barrier. The first conductor  16  is incorporated into the seal  14 , such as by being printed onto the seal  14  or by any other suitable means, and oriented such that breaking the seal  14  necessarily entails also breaking the first conductor  16  without breaking the second conductor  18 . In one embodiment, the seal  14  itself may constitute the first conductor  16 , such as if the seal  14  is a frangible metallic film having a relatively low resistance. 
     When the seal  14  and first conductor  16  are broken, the outside environment is allowed to enter into the interior of the sealed container or package  12  and contact the second conductor  18 . As the outside environment acts upon the second conductor  18 , the resistance (or other variable electrical property) of the second conductor  18  will change over time, as described above. In the embodiment shown in  FIG. 3 , the resistance of the second conductor  18  changes linearly over time with exposure to the outside environment, but in other embodiments, the resistance or other variable electrical property of the second conductor  18  may change exponentially over time or according to any other profile. 
     If the initial resistance of the second conductor  18  (before it is acted upon by the outside environment) and the manner in which the resistance of the second conductor  18  changes over time are known, then the resistance of the second conductor  18  at a particular time may be used to determine when the seal  14  and first conductor  16  were broken (i.e., when the second conductor  18  was first exposed to the outside environment and its resistance started to change). For example, assume that the measured resistance of the second conductor  18  is twice that of the initial resistance of the second conductor  18 . Assume also that it is known how the resistance of the second conductor  18  will change after being exposed to environmental conditions of the type to which the second conductor  18  is exposed after the seal  14  and first conductor  16  have been broken. With these three pieces of information (i.e., the initial resistance of the second conductor  18 , the measured resistance of the second conductor  18 , and the way in which the resistance of the second conductor  18  changes as a function of time and exposure to the environment), it is possible to determine how long the second conductor  18  has been exposed to the outside environment. From there, one may count backwards from the current time to ascertain the time at which the seal  14  and the first conductor  16  were broken. 
       FIG. 4  and  FIG. 5  show two different exemplary systems  20  and  22 , respectively, for determining the resistance of the second conductor  18 . In the embodiment of  FIG. 4 , the system  20  includes a circuit  10  of the type shown in  FIG. 1 , with a first conductor  16  and a second conductor  18  connected in parallel. The conductors  16  and  18  are additionally connected in parallel to a capacitor  24 . One end of the conductors  16  and  18  and the capacitor  24  is connected to ground  26 , while the other end is connected to an input/output port  28  of a monitoring device, such as a microcontroller or remote frequency identification (“RFID”) chip or some other monitoring system. 
     In use, the input/output port  28  is set as an output and the capacitor  24  is initially charged to or near the system supply voltage V 0 . The input/output port  28  is then set as an input and the time required for the voltage V on the capacitor  24  to drop from V 0  to a threshold value V T  (i.e., a value at which a processor or controller associated with the input/output port  28  reads the input as a digital 0 instead of a digital 1) is determined. If only the second conductor  18  is functional (on account of the first conductor  16  being broken, typically along with an associated seal), current will flow through the second conductor  18 , with the voltage V on the capacitor  24  dropping at a rate which depends upon the resistance of the second conductor  18 . Knowing the time taken for the voltage V on the capacitor  24  to drop to the threshold value V T  and the relationship between capacitor voltage and conductor resistance, the present resistance of the second conductor  18  may be derived, which may be used to determine the time at which the first conductor  16  and the seal associated therewith were broken, as described above. 
       FIG. 6  illustrates a possible profile for the voltage V on the capacitor  24  of  FIG. 4 . As described above, an input voltage is applied to charge the capacitor  24  until it reaches a target voltage V 0 . Thereafter, the input/output port  28  is set as an input and the capacitor  24  is allowed to discharge through the second conductor  18 , which decreases the voltage as shown in  FIG. 6 . Although the voltage across the capacitor  24  is shown as decreasing exponentially with time, the resistance of the second conductor  18  will increase linearly with time. In particular, the voltage V across the capacitor  24  may be expressed by the following equation: 
                     V   =       V   0     ⁢     e       -   t       R   ⁢           ⁢   C             ,           (   1   )               
in which t is the amount of time that the capacitor  24  has been discharging, R is the resistance of the second conductor  18  and C is the capacitance of the capacitor  24 .
 
     Equation (1) may be rearranged to isolate the voltages as follows: 
                       V     V   0       =     e       -   t       R   ⁢           ⁢   C           ,           (   2   )               
which may be further rearranged to:
 
     
       
         
           
             
               
                 
                   
                     
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                         ( 
                         
                           V 
                           
                             V 
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                         R 
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                         C 
                       
                     
                   
                   , 
                   and 
                 
               
               
                 
                   ( 
                   3 
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                     R 
                     ⁢ 
                     
                         
                     
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                         ( 
                         
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                   = 
                   
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                       t 
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                   ⁢ 
                   
                     ( 
                     4 
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     As shown in equation (4), the resistance R is inversely related to the time t by a multiplier which may be expressed as a value k as follows: 
     
       
         
           
             
               
                 
                   
                     C 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       ln 
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                         ( 
                         
                           V 
                           
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                   = 
                   
                     k 
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                   ( 
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     Finally, equation (4) may be rewritten using k:
 
 Rk=−t   (6),
 
which shows that resistance R changes linearly with time, i accordance with the resistance profile shown in  FIG. 3 .
 
     In the embodiment of  FIG. 5 , the system  22  includes a circuit  10  of the type shown in  FIG. 1 , with a first conductor  16  and a second conductor  18  connected in parallel. The circuit  10  further includes a resistor  30  in series with the conductors  16  and  18 , with the resistor  30  having a known resistance. The system  22  also includes an analog-to-digital converter  32  connected to opposite ends of the resistor  30 . In use, a voltage is applied to the circuit  10 , with the voltage seen by the analog-to-digital converter  32  being proportional to the ratio of the resistance of the resistor  30  and the resistance of the first and second conductors  16  and  18  (if the first conductor  16  is still intact) or just the second conductor  18  (if the first conductor  16  has been broken) and the voltage applied. If the resistance of the first conductor  16  is much less than the resistance of the second conductor  18 , then the voltage seen by the analog-to-digital converter  32  will be very small (e.g., close to zero) when the first conductor  16  is intact. When the first conductor  16  and associated seal have been broken in an embodiment, the parallel conductor arrangement provides a high resistance/open circuit, with current passing through the relatively high resistance second conductor  18  (and the resistor  30 ), which determines the voltage seen by the analog-to-digital converter  32 . When the ratio of the resistances of the resistor  30  and the second conductor  18  has been determined, the present resistance of the second conductor  18  may be derived, because the resistance of the resistor  30  is already known. Then, the resistance of the second conductor  18  may be used to determine the time at which the first conductor  16  and the seal associated therewith were broken, as described above. 
     While  FIGS. 4 and 5  illustrate two possible monitoring devices or components of monitoring devices that may be incorporated into or associated with a circuit according to the present disclosure, it should be understood that other types of monitoring devices and electrical circuit components may also be incorporated into the circuit without departing from the scope of the present disclosure. Preferably, the monitoring device is configured to communicate or otherwise transmit data about the status of the circuit and/or seal (e.g., via Bluetooth or WiFi or UHF or the like) without constituting a continuous power drain. For example, it may be advantageous to omit a real-time clock from the circuit, because such a device typically requires a battery and constitutes a continuous power drain. 
     In one embodiment, the monitoring device is associated with or incorporates a separate processor or controller or the like that is responsible for data communication. The processor/controller may take any of a variety of suitable forms, from something relatively simple (e.g., a printed electronic device that is configured to communicate with a telephone or other device using a near field communication-compatible “tag talks first” protocol) or something more sophisticated that can accommodate a more complex data link, such as WiFi. It may be advantageous to be particularly aware of power consumption when selecting a paired monitoring device and processor/controller, in which case simpler options (e.g., a simple microcontroller that is running relatively slowly or an RFID link that is powered by the reading device or processor or controller) may be preferred. 
       FIG. 7  illustrates one particular application in which systems according to the present disclosure may be employed. In  FIG. 7 , a medication container includes at least one medication-containing cell  34 . Each cell  34  may be formed of any suitable material but, in one embodiment, each cell is formed of a plastic material or another material that is substantially non-conductive. It may be advantageous for the cells  34  to be formed of a material that is generally rigid, but sufficiently deformable that a human may deform the individual cells using a finger or digital force and manipulation. In a preferred embodiment, the body of the medical container takes the general form of a blister pack, with a thin plastic sheet being provided with a plurality of vacuum-formed depressions or formations that each defines a cell  34  for receiving a dose of medication. While it may be preferred for a medication container having a plurality of cells to be provided with a single plastic sheet that is formed to define all of the cells, it is also within the scope of the present disclosure for the cells of a single medication container to be separately or non-integrally formed. 
     Each cell  34  is closed or overlaid by a cover or seal  36  through which medication within the cell  34  may be accessed. In one embodiment, the seal  36  is a thin sheet of material, such as a metallic foil or the like, which may be broken to allow a medication to pass out of the cell  34 . In such an embodiment, a base of the cell  34  may be pressed toward the frangible seal  36  by a user until the force on the seal  36  exceeds the strength of the seal  36 , at which point the seal  36  breaks and the medication may be removed from the cell  34 . Alternatively, the cell  34  may remain untouched, while the seal  36  is directly engaged and broken to remove medication from the cell  34 . If the medication container is provided with a plurality of cells, it may be preferred for a single seal to overlay all of the cells, but it is also within the scope of the present disclosure for two or more cells of the same medication container to be provided with separate seals. For example, in one embodiment, different cells are each overlaid by separate, non-frangible (e.g., hinged) covers or seals. 
     In the embodiment of  FIG. 7 , a circuit  10  of the type shown in  FIG. 1  can be incorporated into the medication container. In such an embodiment, the circuit  10  is arranged such that the first conductor  16  extends over the cell  34 , with the seal  36 , while the second conductor  18  is positioned adjacent to the cell  34  without passing over the cell  34 . In a particular embodiment, the circuit  10  may be printed onto the seal  36  or otherwise integrated into the seal  36 , but it also within the scope of the present disclosure for the circuit  10  to be separately provided from the seal  36 . In another embodiment, the first conductor  16  may be the foil cover that seals the cell  34 , with such a first conductor  16  providing a low resistance acting as a virtual short (when intact) and later having an effectively infinite resistance (when broken) which directs all current through the second conductor  18 , allowing the monitoring device or system to “see” the second conductor  18 . The second conductor  18  may be fabricated with a barrier that protects the second conductor  18  during manufacturing, with the barrier being configured to be breached when the seal  36  is secured (e.g., by heat sealing) to the body of the medication container. Although not illustrated in  FIG. 7 , the circuit  10  may include additional components, such as an input/output port of the type shown in  FIG. 5  and/or an analog-to-digital converter of the type shown in  FIG. 6  or other suitable monitoring device component. 
     Accessing a cell  34  through the seal  36  to remove the medication disrupts the circuit  10  at the location of the cell  34 , particularly by severing or breaking the first conductor  16  at the cell  34 . Breaking the seal  36  and the first conductor  16  exposes the second conductor  18  to the outside environment, causing the resistance of the second conductor  18  to change as a function of time. As described above in greater detail, the resistance of the second conductor  18  at a particular time may be measured and then used to determine the time at which the seal  36  of the medication container was broken. If the medication container includes a plurality of cells, each may include its own associated circuit, thereby allowing a doctor or medical care provider to separately monitor the status of each cell. This may be especially advantageous if the various cells contain different medications that are to be ingested by a subject at particular times. 
       FIG. 8  illustrates another particular application for systems according to the present disclosure. In  FIG. 8 , a sealed package or container includes at least two portions or handles  38  and  40 , with the package or container being configured to be opened or unsealed by moving the handles  38  and  40  apart. In an embodiment, a circuit  10  of the type shown in  FIG. 1  is incorporated into the package or container by wrapping or otherwise securing the first conductor  16  to both handles  38  and  40 , while wrapping or otherwise securing the second conductor  18  to only one of the handles  38 . Although not illustrated in  FIG. 8 , the circuit  10  may include additional components, such as an input/output of the type shown in  FIG. 5  and/or an analog-to-digital converter of the type shown in  FIG. 6  or other suitable monitoring device component. 
     Preferably, the first conductor  16  is frangible and configured such that, when the handles  38  and  40  are separated apart to break the seal on the package or container, the first conductor  16  will also break. Breaking the seal and the first conductor  16  exposes the second conductor  18  to the outside environment, causing the resistance of the second conductor  18  to change as a function of time. As described above in greater detail, the resistance of the second conductor  18  at a particular time may be measured and then used to determine the time at which the seal of the package or container was broken. In a particular embodiment, the first conductor  16  is associated with a sealed passage that exposes the second conductor  18  to atmospheric oxygen when the seal is broken, but the second conductor  18  may be configured to react to other outside environmental conditions without departing from the scope of the present disclosure. Regardless of the particular embodiment, a system of the type shown in  FIG. 8  may be advantageous when shipping a package or container that becomes unsealed during transit, in that it becomes possible to determine whose custody the package or container was in when the seal was broken, which information may be used to determine who bears the responsibility for replacing or paying for the unsealed item. 
       FIG. 9  illustrates an alternative embodiment of a system for determining when a seal has been broken. In the embodiment of  FIG. 9 , the system includes an electrical circuit  42  including a single conductor  44 , as opposed to the dual-conductor circuit  10  of  FIG. 1 . Providing a circuit  42  with only one conductor  44  may result in a system that is less expensive than a system incorporating two conductors. Furthermore, another advantage of a system of the type shown in  FIG. 9  is that an initial calibration of the conductor  44  may be carried out in the sealed state, with the information being stored in either a device (e.g., an RFID chip) local to the circuit  42  or in a separate database or controller/processor associated with the identity of the system. 
     The conductor  44  is environmentally sensitive, such that at least one of its electrical properties will change as a function of time after being exposed to the environment outside of a sealed container, similar to the second conductor  18  of  FIG. 1 . In one embodiment, the conductor  44  is a resistor having a resistance that changes as a function of time after being exposed to the environment outside of the sealed container but, as described above in greater detail with regard to the second conductor  18  of  FIGS. 1 and 2 , the conductor  44  may be any other suitable electrical circuit component. The conductor  44  may be sensitive to any one or more environmental factors. For example, the conductor  44  may be configured to react to a liquid or gas in the outside environment by corroding to some degree in order to change its resistance. A conductor  44  formed of a conductive metal may at least partially convert to an oxide or other non-conducting compound as a mechanism for changing its resistance. An organic conductor (e.g., polyaniline) may have its structure attacked as a mechanism for changing its resistance. Hence, depending on the nature of the outside environment to which the conductor  44  is to be exposed, a particular material may be selected for the conductor  44  to elicit a desirable reaction and predictable resistance change. 
     The initial resistance of the conductor  44  is known, with the resistance of the conductor  44  being equal to this initial resistance when the seal of the associated sealed container or package is intact. When the seal is broken and the conductor  44  is exposed to the outside environment, the resistance of the conductor  44  will increase according to any of a number of possible profiles, such as by increasing linearly or exponentially with time and exposure to the outside environment. Although not illustrated in  FIG. 9 , the circuit  44  may include additional components, such as a monitoring device (e.g., a device having an input/output port of the type shown in  FIG. 4  or an analog-to-digital converter of the type shown in  FIG. 5 ) paired with a processor or controller or the like for determining the resistance of the conductor  44  both before and after the seal has been broken. 
     Providing only an environmentally sensitive conductor  44  (rather than also incorporating an environmentally stable conductor into the circuit  42 ) may make it more difficult to detect the change in electrical property of the conductor  44 , due to the elimination of a clear step change in the property, of the type shown in  FIG. 3 . However, a properly selected monitoring device and processor/controller will be capable of determining the current value of the electrical property and then tracking back to the time of the unsealing event using knowledge of the behavior of the conductor  44  in the presence of the outside environment. Preferably, the conductor  44  is selected to have an electrical property that changes rapidly upon its initial exposure to the outside environment to make it easier for the monitoring device and processor/controller to determine the time at which the seal was broken. It may be especially preferred for the value of the electrical property to initially change quickly (for better accuracy for shorter time periods) and change more slowly over time (resulting in diminished accuracy at longer time periods, but an improved lifespan for the system). Such an embodiment may be advantageous for clinical purposes, in which short term accuracy (e.g., whether a tablet was taken ten minutes ago vs. thirty minutes ago) is more important than long term accuracy (e.g., whether a table was taken eleven hours ago or twelve hours ago). This may also be true for systems according to the present disclosure which incorporate two conductors, rather than a single conductor. 
       FIG. 10  illustrates one particular application in which a single-conductor system of the type shown in  FIG. 9  may be employed. In  FIG. 10 , a medication container of the type described above with respect to  FIG. 7  is provided, with at least one medication-containing cell  34 . Rather than having an environmentally stable conductor associated with a seal  36  extending over the cell  34  and an environmentally sensitive conductor positioned adjacent to the cell  34  without passing over the cell  34 , this illustrated embodiment includes only an environmentally sensitive conductor  44  positioned adjacent to the cell  34  without passing over the cell  34 . Similar to the embodiment of  FIG. 7 , the conductor  44  may be fabricated with a barrier that protects the conductor  44  during manufacturing, with the barrier being configured to be breached when the seal  36  is secured (e.g., by heat sealing) to the body of the medication container. Additionally, although not illustrated in  FIG. 10 , the circuit  42  may include additional components, such as an input/output port of the type shown in  FIG. 5  and/or an analog-to-digital converter of the type shown in  FIG. 6  or other suitable monitoring device component. 
     Accessing a cell  34  through the seal  36  to remove the medication exposes the conductor  44  to the outside environment, causing the resistance of the conductor  44  to change as a function of time. As described above in greater detail, the resistance of the conductor  44  at a particular time may be measured and then used to determine the time at which the seal  36  of the medication container was broken. If the medication container includes a plurality of cells, each may include its own associated circuit, thereby allowing a doctor or medical care provider to separately monitor the status of each cell. This may be especially advantageous if the various cells contain different medications that are to be ingested by a subject at particular times. 
     It will be understood that the embodiments described above are illustrative of some of the applications of the principles of the present subject matter. Numerous modifications may be made by those skilled in the art without departing from the spirit and scope of the claimed subject matter, including those combinations of features that are individually disclosed or claimed herein. For these reasons, the scope hereof is not limited to the above description but is as set forth in the following claims, and it is understood that claims may be directed to the features hereof, including as combinations of features that are individually disclosed or claimed herein.