Abstract:
A container security system has a container interior monitor portion with a container interior light sensing portion responsive to visible light. A different embodiment involves a monitoring device with a support, a door engaging member movable to and from an operational position, and a detection portion that generates an electrical signal in response to movement of the member away from the operational position. The support may be configured to be supported on an edge portion of a movable door. Alternatively, the monitoring device may include a wireless communication portion, and circuitry responsive to the signal and operatively coupled to the wireless communication portion.

Description:
[0001]     This application claims the priority under 35 U.S.C. §119 of U.S. provisional application No. 60/514,968 filed Oct. 27, 2003, the disclosure of which is hereby incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates in general to monitoring and security for containers and, more particularly, to devices that provide automated monitoring and security for shipping containers.  
       BACKGROUND  
       [0003]     A variety of different products are shipped in cargo containers. Products are packed into the container by a shipper, after which the container doors are closed and then secured with some type of lock. The container is then transported to a destination, where a recipient removes the lock and unloads the container.  
         [0004]     The shipper often finds it advantageous to have some form of monitoring while the container is being transported. For example, the cargo within the container may be relatively valuable products such as computers or other electronic devices, and thieves may attempt to break into the container and steal these products if the container is left unattended during transport. Alternatively, the cargo may be products such as fresh fruit, for which it is advantageous to continuously monitor environmental conditions such as temperature and humidity, in order to avoid or minimize spoilage.  
         [0005]     It is not cost-feasible to have a person watch a container at all times in order to provide security and/or monitoring. Accordingly, electronic systems have previously been developed to provide a degree of automated security and/or monitoring. Although these pre-existing systems have been generally adequate for their intended purposes, they have not been satisfactory in all respects.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]     A better understanding of the present invention will be realized from the detailed description that follows, taken in conjunction with the accompanying drawings, in which:  
         [0007]      FIG. 1  is a diagrammatic perspective view of an apparatus that includes a container and a security and monitoring device, and that embodies aspects of the present invention;  
         [0008]      FIG. 2  is a diagrammatic fragmentary front view of a portion of the apparatus of  FIG. 1 , in a significantly enlarged scale;  
         [0009]      FIG. 3  is a diagrammatic top view of the security and monitoring device of  FIG. 1 , without the shipping container;  
         [0010]      FIG. 4  is a diagrammatic perspective view of the rear side of the security and monitoring device;  
         [0011]      FIG. 5  is a diagrammatic perspective bottom view of the security and monitoring device, with certain structural parts omitted for clarity; and  
         [0012]      FIG. 6  is a diagrammatic perspective top view of the security and monitoring device, with certain structural parts omitted for clarity.  
     
    
     DETAILED DESCRIPTION  
       [0013]      FIG. 1  is a diagrammatic perspective view of an apparatus  10  that includes a container  11 , and a security and monitoring device  12 . The security and monitoring device  12  embodies aspects of the present invention, and is discussed in more detail later.  
         [0014]     The container  11  is a conventional shipping container of a well-known type, and in particular complies with an industry-standard specification known as an ISO 668:1995(E) Series 1 freight container. The vast majority of containers that are currently in commercial use conform to this ISO standard. This particular type of container is shown by way of example. The present invention is not limited to this particular type of container, or to containers in general.  
         [0015]     The container  11  is made almost entirely of steel or aluminum, except that a not-illustrated floor within the container may be made of either wood or metal. The container  11  has at one end a large opening  14  with an approximately square shape. Two rectangular doors  16  and  17  are supported by hinges for pivotal movement about respective spaced vertical axes  18  and  19 . The axes  18  and  19  are located near respective side edges of the opening  14 . The doors  16  and  17  are each shown in a closed position in  FIG. 1 , and can each pivot about 90° to 270° outwardly from this position to an open position, which is not shown in the drawings.  
         [0016]     The doors  16  and  17  each have a respective vertical outer edge  21  or  22 , which is disposed adjacent the associated pivot axis  18  or  19 . In addition, each of the doors  16  and  17  has a respective inner edge portion  23  or  24 . When the doors  16  and  17  are in the closed position of  FIG. 1 , the inner edge portions  23  and  24  are adjacent, with a small gap between them. According to the ISO standard, the inner edge portions  23  and  24  of the doors  16  and  17  are each an approximately rectangular metal part, with a cross-sectional size of about 45 mm by 95 mm. For example, the door edge portions  23  and  24  may be rectangular steel tubes of this size.  
         [0017]     In order to secure the doors  16  and  17  in their closed positions, the door  16  has two vertical rods  31  and  32  rotatably supported thereon, and the door  17  has two vertical rods  33  and  34  rotatably supported thereon. Each of the rods  31 - 34  has a respective handle  36 - 39  thereon. The handles  36 - 39  can be used to manually rotate the rods  31 - 34  between locked and released positions. In the locked position, each handle can engage a retention bracket mounted on the associated door, and the bracket maintains the handle and rod in the locked position. As each rod is pivoted between its locked and released positions, each end thereof can move into or out of engagement with a locking bracket or locking recess provided on the container  11 .  
         [0018]     The door  16  has three corrugations or recesses  43 - 45  that extend horizontally and are vertically spaced. Similarly, the door  17  has three corrugations or recesses  46 - 48  that extend horizontally and are vertically spaced.  
         [0019]     When the container  11  has been packed with products that are to be shipped, various considerations can come into play. First, there are situations in which it is desirable to be able to monitor environmental conditions within the container. For example, products such as fresh fruit may keep better if environmental conditions within the container  11  remain within certain acceptable limits, and so it is desirable to monitor relevant environmental conditions such as temperature or humidity. Another consideration is that, once the doors  16  and  17  have been closed and secured at the point of shipment, there are situations in which it is desirable to have some form of security and monitoring in order to verify that the doors are not opened again until the container arrives at its destination. For example, while the container is in transit, thieves may attempt to break into the container  11  in order steal valuable cargo therein, such as computers or other electronic devices. In order to handle these various different types of situations, the device  12  provides security and monitoring capability with respect to both environmental conditions and container intrusion.  
         [0020]      FIG. 2  is a diagrammatic fragmentary front view of a portion of the apparatus of  FIG. 1 , in a significantly enlarged scale. The structure and operation of the security and monitoring device  12  are discussed in detail later, but some aspects of the device  12  can be seen in  FIG. 2 . The device  12  includes a resilient metal support clip  61 . The support clip  61  is approximately C-shaped, and grips around the rectangular edge portion  24  of the door  16 , in order to removably support the device  12  on the door  16 . An anti-tamper part  62  is provided on the support clip  61 , on the inner side of the doors. A wireless communication module  63  is mounted on an outer side of the support clip  61 , and the support clip  61  has at one end a tab  64  that projects outwardly beyond the wireless communication module  63 . The wireless communication module  63  has a relatively low profile, to reduce the likelihood that it would be struck and damaged by some other device.  
         [0021]      FIG. 3  is a diagrammatic top view of the device  12 , without the shipping container. The resilient metal support clip  61  is a single integral part and, as mentioned above, is bent to have approximately a C-shape. In particular, the support clip  61  has spaced leg portions  71  and  72 , and a bight portion  73  that extends between and is coupled to respective ends of the leg portions  71  and  72 . The tab  64  is provided at an outer end of the leg portion  71 , and is inclined at a slight angle to the remainder of the leg portion  71 , so as to define an inclined surface portion  76 . The outer end of the leg portion  72  is bent to define an inclined portion  77  that extends at an angle to the main part of the leg portion  72 , and a further inclined portion  78  that extends at an angle to the inclined portion  77 . The inclined portions  77  and  78  define respective inclined surface portions  81  and  82 .  
         [0022]     When the device  12  is being installed on the edge portion  24  of the door  16  ( FIG. 2 ), the device  12  is manually moved toward the edge portion  24  in the direction indicated by an arrow  83 . The inclined surface portions  76  and  82  engage outer corners of the edge portion  24  of the door  16 , and help to spread the leg portions  71  and  72  against the inherent resilience of the support clip  61 . The inclined portions  64 ,  78  and/or  77  can also be manually grasped in order to help manually spread the leg portions  71  and  72 , to facilitate installation of the device  12  on the door edge portion  23 .  
         [0023]     After the door edge portion  23  is fully received within the support clip  61 , the inclined surface portion  81  engages an inner corner of the rectangular door edge portion  23 . In association with the resilience of the support clip  61 , the inclined surface portion  81  continuously and yieldably urges the support clip  61  in the direction of the arrow  83  with respect to the door edge portion  23 . This maintains the support clip  61  in place, and actively resists its unintended removal. In fact, as the support clip  61  is being installed on the edge portion  23 , and once the inclined surface  81  has moved into engagement with an inner corner of the edge portion  23 , the surface  81  and the resilience of the support clip  61  will tend to cause the support clip  61  to automatically snap to its final position.  
         [0024]     The device  12  can be removed from the door edge portion  23  by manually pulling the device  12  in a direction opposite the arrow  83 . The engagement of the inclined surface  81  with an inner corner of the edge portion  23  will help to spread the leg portions  71  and  72  against the resilience of the support clip  61 . In addition, if necessary, the tab  64  and the inclined portion  78  or  77  can be grasped and manually pulled apart, in order to help spread the leg portions  71  and  72 .  
         [0025]     The inner side of the leg portion  71  has a plurality of approximately hemispherical bosses  86 , which each project toward the opposite leg portion  72 . The bight portion  73  has a plurality of similar bosses  87  on the inner side thereof. The bosses  86  and  87  serve as gripping structure that helps resist movement of the support clip  61  relative to the door edge portion  23 . In particular, the bosses resist detachment of the support clip  61  due to movement in a horizontal direction opposite the arrow  83 , and also resist vertical downward sliding movement of the support clip  61  along the door edge portion  23 . In place of the bosses  86  and  87 , it would alternatively be possible to provide gripping structure in the form of a non-slip sheet  88  that is securely mounted to one or more of the inner surfaces of the support clip  61 . The sheet  88  could, for example, be made of rubber or some other suitable non-slip material.  
         [0026]     A sensor module  91  is mounted on the leg portion  72  of the support clip  61 . An outer housing of the sensor module  91  is visible in  FIG. 3 . This housing is held in place by several fasteners  89 , such as rivets or screws. Within the housing, the sensor module  91  has circuitry and other structure that is discussed later. The circuitry includes sensors which can monitor conditions within the container, including environmental conditions like temperature and humidity.  
         [0027]     A metal lever  92  is disposed behind the anti-tamper part  62 . The lever  92  can move in relation to the anti-tamper part  62 , in a manner described in detail later. A pivot axle  94  is fixedly supported near an outer end of the lever  92 , and pivotally supports a door-engaging member  93 , as described in more detail later. In the disclosed embodiment, the member  93  is made of plastic, but it could alternatively be made of any other suitable material. The member  93  has a door-engaging surface  96 , which can slidably engage an inner surface of the door edge portion  24  of the door  17  ( FIG. 2 ).  
         [0028]      FIG. 3  shows in broken lines an optional reader  97 , which is a type of device that is known in the art. The reader  97  is physically separate from the device  12 , and would be physically mounted on an inner surface of the container, at a location spaced from the device  12 . The reader  97  would be electrically coupled at  98  to the circuitry within the sensor module  91 . This electrical coupling could, for example, be in the form of an interface conforming to an industry standard known as RS-485. Broadly speaking, the reader  97  can function as a form of sensor. For example, when the container  11  contains products or pallets that carry radio frequency identification (RFID) tags of a type known in the art, the reader  97  can collect information from the tags through radio frequency signals, and can then pass the collected information at  98  to the circuitry within the sensor module  91 . Thus, the inventory within the container can be automatically and continuously monitored electronically.  
         [0029]      FIG. 4  is a diagrammatic perspective view of the rear side of the device  12 . It will be noted that the housing of the sensor module  91  has a rear wall with a cluster of holes  101  extending through it. These holes  101  provide the sensors inside the sensor module  91  with suitable access to ambient air, in order to achieve accurate sensing and monitoring of conditions such as temperature and humidity.  FIG. 4  shows that the anti-tamper part  62  has a pair of spaced, rearwardly-projecting tabs  106  and  107 , which are disposed on opposite sides of the lever  92 . The portion of the lever  92  which is visible in  FIG. 4  is capable of limited forward and rearward movement, toward and away from the anti-tamper part  62 , as discussed in more detail later.  
         [0030]     Two plastic supports  111  and  112  are fixedly mounted at spaced locations on the outer end of the lever  92 , and fixedly support the pivot axle  94 . The door-engaging member  93  has two spaced side portions that cooperate with the ends of the axle  94 , so that the member  93  can pivot on the axle  94  with respect to the lever  92  and the supports  111  and  112 . Two coil springs  113  and  114  encircle the axle  94  between the supports  111  and  112 . The coil spring  113  has one end coupled to the support  111 , and its other end coupled to the member  93 . Similarly, the coil spring  114  has one end coupled to the support  112 , and its other end coupled to the member  93 . The coil springs  113  and  114  urge the member  93  to pivot relative to the lever  92 , in a direction indicated by an arrow  118 .  
         [0031]      FIG. 5  is a diagrammatic perspective bottom view of the device  12 , with selected parts omitted for clarity. In particular, the housing is omitted from the sensor module  91 , and the supports  111 - 112 , springs  113 - 114 , axle  94  and member  93  are omitted from the outer end of the lever  92 . A planar metal base plate  131  is fixedly secured to the leg portion  72  of the support clip  61 . In the disclosed embodiment, the base plate  131  is fixedly secured to the leg portion  72  by a double-sided adhesive sheet  132 . However, the base plate  131  could alternatively be mounted on the leg portion  72  in any other convenient and suitable manner.  
         [0032]     The base plate  131  has two rearwardly-projecting flanges  133  disposed on opposite sides thereof, and two spaced holes  134  are provided through each flange  133 . The fasteners  89  ( FIG. 4 ) cooperate with the holes  134  in order to hold the housing of the sensor module  91  in place. In  FIG. 5 , the left end of the base plate  131  has a portion that projects outwardly beyond the bight portion  73  of the support clip  61 , in order to serve as the anti-tamper part  62  with the previously-mentioned tabs  106  and  107 .  
         [0033]     Two spaced metal studs  137  are fixedly mounted on the base plate  131 . The lever  92  extends between the studs  137 , and has in each side edge a not-illustrated recess that receives a respective stud  137 , in order to prevent any significant lengthwise movement of the lever  92 . A retainer  138  extends between the studs  137 , and has holes that receive the studs  137  with a friction fit. The lever  92  can rock or pivot about a pivot axis located adjacent and parallel to the retainer  138 . A conical coil spring  139  is disposed between the base plate  131  and the right end of the lever  92 . The spring  139  resiliently urges the right end of the lever  92  in a rearward direction away from the base plate  131 , which means that the left end of the lever  92  is resiliently urged in a forward direction, as indicated by an arrow  140 .  
         [0034]     Four parallel cylindrical supports  140  are each fixed at one end to the base plate  131 , and project outwardly therefrom. A circuit board  142  is secured to the outer ends of the supports  141  by a plurality of screws  143 . The device  12  includes a not-illustrated battery, which provides electrical power to circuitry within the device  12 , including the circuitry on the circuit board  142 . Since  FIG. 5  is diagrammatic, it does not show all of the circuit components that are mounted on the circuit board  142 . Instead,  FIG. 5  shows only selected components that are relevant to an understanding of the present invention.  
         [0035]     In this regard, four sockets  151 - 154  are all mounted on the side of the circuit board  142  facing away from the lever  92 , and are each coupled electrically to a bus that is part of the circuitry on the circuit board  142 . The sockets  151 - 154  permit sensors to be easily added to and removed from the device  12  in a modular fashion.  FIG. 5  shows a temperature sensor  157  removably inserted in the socket  151 , and a humidity sensor  158  removably inserted in the socket  152 . The sockets  153  and  154  are shown as empty, but could receive other types of sensors, including but not limited to a pressure sensor, a moisture sensor, a vibration sensor, a shock sensor, a radiation sensor (for detecting radioactive emissions), and/or a gas sensor (for detecting hazardous or poisonous gases, such as hydrogen cyanide, or phosgene).  
         [0036]     A known type of light sensor  162 , such as a photocell, is mounted on the circuit board  142  adjacent one edge thereof. The housing for the sensor module  91  has a small opening in one side thereof, which is not visible in the drawings. This opening is adjacent to the light sensor  162 , and permits the light sensor  162  to monitor whether or not there is visible light within the container.  
         [0037]     A ribbon cable  164  has one end electrically coupled to the circuit board  142 . From the circuit board  142 , the ribbon cable  164  extends through aligned openings in the lever  92 , the base plate  131 , and the leg portion  72  of the support clip  61 , and then extends along inner surfaces of the bight portion  73  and the leg portion  71  of the support clip  61 . The ribbon cable  164  is adhesively secured to these inner surfaces of the support clip  61 , but could alternatively be held in place in any other suitable manner. The ribbon cable  164  then passes through an opening  167  provided in the leg portion  71 , and into the wireless communication module  63 . This end of the ribbon cable  164  is electrically coupled to not-illustrated circuitry that is provided within the wireless communication module  63 .  
         [0038]      FIG. 6  is a diagrammatic perspective top view of the device  12 , showing the same structure as  FIG. 5 , but from a different angle.  FIG. 6  shows a stop  174  which is fixedly mounted on the lever  92 , and which can engage the circuit board  142  in order to limit movement of that end of the lever  92  toward the circuit board  142  under the urging of the coil spring  139 .  FIG. 6  also shows a header or connector  176  which is provided at one end of the ribbon cable  164 , in order to facilitate an electric coupling of the ribbon cable  164  to the circuit board  142 .  
         [0039]     Two Hall effect sensors  177  and  178  are provided on the side of the circuit board  142  facing the lever  92 , and serve as proximity sensors. Two magnets  181  and  182  are fixedly mounted on the adjacent end of the lever  92 , in a manner so that each magnet is aligned with a respective one of the Hall effect sensors  177  and  178 . As the lever  92  undergoes reciprocal pivotal movement, the magnets  181  and  182  move toward and away from the Hall effect sensors  177  and  178 , and serve as magnetic field generators that actuate and deactuate the Hall effect sensors. The stop  174  ensures that the magnets  181  and  182  can come close to the sensors  177  and  178  but do not touch the sensors, for example to avoid damage to or wear of the magnets or sensors.  
         [0040]     The foregoing discussion includes an explanation of how the security and monitoring device  12  can be removably installed on the door  16  of the container  11 , and removed from the door. Now, a brief explanation of the operation of the device  12  will be provided. For the purpose of this discussion, it is assumed that the device  12  has already been installed on the edge portion  23  of the door  16 .  
         [0041]     With reference to  FIG. 5 , the coil spring  139  resiliently urges pivotal movement of the lever  92  in a direction that causes the opposite end of the lever  92  to be urged in the direction of the arrow  140 , or in other words in a direction away from the interior of the container. In addition, with reference to  FIG. 4 , the coil springs  113  and  114  urge pivotal movement of the door-engaging member  93  in the direction of the arrow  118 , which means that the door-engaging surface  96  is urged in a direction away from the interior of the container. The spring  139  and the springs  113  and  114  are selected so that, with respect to the member  93 , the springs  113  and  114  collectively exert an effective force that is greater than the effective force exerted by the spring  139  through the lever  92 . Stated differently, when an external force is exerted on the door-engaging surface  96 , the lever  92  will pivot relative to the sensor module  91  before the member  93  pivots relative to the lever  92 .  
         [0042]     As a specific example, assume that the container door  16  with the device  12  thereon is in its closed position, and that the container door  17  is being moved from its open position to its closed position. The edge portion  24  of the door  17  will engage the door-engaging surface  96  on the member  93 , and press the member  93  toward the interior of the container. As the member  93  is moved inwardly, the member  93  will not initially pivot with respect to the lever  92 , but instead the lever  92  will pivot against the force of the coil spring  139 . The coil spring  139  will be compressed and, with reference to  FIG. 6 , the magnets  181  and  182  will move away from the Hall effect sensors  177  and  178 .  
         [0043]     At some point, the lever  92  will reach the end of its effective range of pivotal movement. Then, as the door  17  continues to close, the lever  92  will remain stationary, and the door-engaging member  93  will pivot about the axle  94  in relation to the lever  92 , until the door  17  is in its closed position. The provision of the movable member  93 , in association with the relative strengths of the various springs, ensures that the lever  92  will be moved to and maintained in its actuated position, even if the doors  16  and  17  are not entirely coplanar, or if one of the doors is bent or otherwise has some skew. That is, the movable member  93  and the relative strengths of the springs permit the movable member  93  to accommodate misalignment or play in the positions of the two container doors, while ensuring that the lever  92  is reliably moved between its actuated and deactuated positions as the door  17  is moved to and from its closed position.  
         [0044]     Assume now that, after both of the containers doors  16  and  17  have been moved to and secured in their closed positions, the container  11  is dispatched for transport to a remote destination. In addition, assume that someone opens the door  17  without authorization while the container is en route to its destination. As the door  17  is being opened, the springs  113  and  114  will initially pivot the door-engaging member  93  back to its original position, while the lever  92  remains stationary. Then, as the door  17  continues to open, the spring  139  will pivot the lever  92  back to its original position, which is shown in  FIG. 6 . As this occurs, the magnets  181  and  182  will be moved back to positions adjacent the Hall effect sensors  177  and  178 . The output signals from the Hall effect sensors  177  and  178  will therefore change, and the circuitry on the circuit board  142  can detect this change.  
         [0045]     The circuitry on the circuit board  142  can then send signals through the ribbon cable  164  to the wireless communication module  63 . The module  63  contains a not-illustrated radio frequency (RF) antenna of a known type, as well as not-illustrated support circuitry of a known type, including a radio transceiver and a microprocessor. The wireless communication module  63  can respond to the information received through the ribbon cable  164  by transmitting a wireless signal that indicates the container door  17  has been opened. A not-illustrated reader of a known type, which is at a remote location, can receive this wireless signal and take appropriate action. For example, security personnel can be dispatched to check on the container  11 , and may arrive in time to apprehend the person who opened the container without authorization.  
         [0046]     The member  93 , springs  113 - 114 , lever  92 , spring  139 , magnets  181 - 182  and Hall-effect sensors  177 - 178  can be collectively viewed as a sensing portion that monitors the closed status of the container doors. Within this sensing portion, the springs  113 - 114 , the lever  92 , the spring  139 , the magnets  181 - 182  and the sensors  177 - 178  collectively serve as a detection arrangement for detecting movement of the member  93 , and the magnets  181 - 182  and sensors  177 - 178  effectively serve as a sensing arrangement within the detection arrangement.  
         [0047]     With reference to  FIG. 5 , and as discussed above, the light sensor  162  monitors the amount of visible light that is present within the container. If the container doors are both closed, then the interior of the container will typically be dark. On the other hand, if either of the doors is open, or if there is a hole or some other breach in a container wall, ambient light can enter the container. Also, even if the container is closed, visible light can be produced within the container by a device such as a flashlight. To the extent visible light is present within the container, the light sensor  162  can detect this, and will change the output signal that it is sending to the circuitry on the circuit board  142 . This circuitry can then send a signal through the ribbon cable  164  to the wireless communication module  63 , which in turn can transmit a radio signal indicating that a door was apparently opened. Security personnel can then be dispatched to the container.  
         [0048]     Still referring to  FIG. 5 , the sensors  157  and  158  each monitor a condition within the container, such as an environmental condition. The output signals from the sensors  157  and  158  are each monitored by the circuitry on the circuit board  142 . In the disclosed embodiment, and as mentioned above, the sensor  157  is a temperature sensor. Assume that the container is being used to transport fresh fruit, and that the container is unexpectedly delayed for some reason during unusually hot summer weather. If the circuitry on the circuit board  142  finds that the temperature within the container has increased to a point where rapid spoilage of the fresh fruit becomes likely, the circuitry can transmit a signal through the ribbon cable  164  to the wireless communication module  63 , which in turn can transmit a radio signal containing an appropriate warning, so that a human may be able to take appropriate action to remedy the situation before the fruit actually spoils.  
         [0049]     With reference to  FIG. 3 , if the reader  97  is present, and if there are products or pallets within the container that carry RFID tags, the reader  97  can collect information from the tags, for example to establish and monitor an inventory of what is present within the container. If anything within the container is removed (along with its RFID tag) the reader  97  can detect this. The reader  97  communicates through the interface  98  with the circuitry on the circuit board  142 . If either the reader  97  or the circuitry decides there is a problem, a signal can be sent through the ribbon cable  164  to the wireless communication module  63 , which can then transmit a radio signal that provides notification of the problem.  
         [0050]     A person who is familiar with the device  12  might try to defeat its operation by inserting a thin object through the gap between the edge portions  23  and  24  of the closed container doors. In order to make this difficult or impossible, the device  12  includes the anti-tamper part  62 . On a more specific level, if the anti-tamper part  62  were omitted, a thin object could be inserted between the doors, and could be used to hold the lever  92  in its actuated position while opening the door  17 . Consequently, the device  12  might not detect a problem and generate an alarm. However, the anti-tamper part  62  serves as an obstruction that prevents such an inserted object from easily contacting the lever  92 . Further, the tabs  106  and  107  are provided at the top and bottom edges of the anti-tamper part  62 , in order to make it difficult for a thin object to be inserted around either the top or the bottom of the anti-tamper part  62 .  
         [0051]     As discussed above, the resilient support clip  61  securely and removably holds the device  12  in place on a container. This is in contrast to a variety of existing devices, which are attached to containers in a permanent or semi-permanent manner, for example using adhesives, bolts, rivets, or the like. The resilient support clip  61  thus permits the device  12  to be quickly and easily installed, and to be quickly and easily removed. This allows the owner of the device  12  to easily move the device  12  from container to container, as needed. In this regard, shippers often lease containers, and it is the shipper rather than the container owner who has the most concern about security and monitoring of the cargo. The device  12  can be owned by a shipper, can be easily installed by the shipper on a leased container, and can later be easily removed by the shipper when the container is to be returned to its owner. As discussed above, the device  12  is specifically designed to be compatible with a particular ISO standard, and the vast majority of containers that are currently in commercial use conform to this particular ISO standard. A shipper will thus find that the device  12  can be readily interchanged among the vast majority of containers that are in commercial use. Of course, while the device  12  is advantageous in association with this particular type of shipping container, it is not limited to use with such a container.  
         [0052]     With respect to a given container, the device  12  can be easily and quickly repositioned on the container, for example to avoid interference between the device and a particular cargo packed inside the container, or to position the device  12  for optimum monitoring of a specific environmental condition in the container during a particular shipment. In this regard, it may be desirable in some circumstances to monitor temperature near the top of the container interior, or to check for heavier-than-air gases near the bottom of the container interior.  
         [0053]     Although the device  12  can be positioned at a variety of locations along the edges of a container door, an advantage of the device  12  is that it can be mounted on one door so that it is adjacent to and monitors an edge of another door, where the monitored edge is opposite from the hinges of the other door. This permits the device  12  to be more sensitive to a door-opening condition than units that are installed on or near a door hinge. This is because, during a given amount of pivotal movement of a door, the leading edge of the door moves significantly farther than a portion of the door near the hinge.  
         [0054]     In the disclosed embodiment, and with reference to  FIG. 5 , the circuit board  142  has several of the sockets  151 - 154  that can removably receive sensors such as those shown at  157 - 158 . Thus, in the disclosed embodiment, the sensors are disposed within the sensor module  91 , and are effectively part of the device  12 . However, it would alternatively be possible for some or all of the sensors to be physically separate from the device  12 . For example, an industry-standard electrical connector could be electrically coupled to the circuitry on the circuit board  142 , and could be physically mounted on the exterior of the housing of the sensor module  91 . One or more sensors could be mounted in the interior of the container at locations spaced from the device  12 , and could be electrically coupled to the device  12  through cables that attach to the electrical connector on the sensor module housing. The electrical interface between the device  12  and each such sensor could conform to an industry standard such as that known as an RS-485 serial bus, which would permit a plurality of different sensors to all be coupled in a modular manner to a single serial bus.  
         [0055]     Although a selected embodiment has been illustrated and described in detail, a variety of substitutions and alterations are possible without departing from the spirit and scope of the present invention, as defined by the following claims.