BACKGROUND  
       [0001]     1. Field of the Invention  
         [0002]     The present invention generally relates to a system and method to provide passive anti-theft protection for a removable entertainment device.  
         [0003]     2. Description of Related Art  
         [0004]     Media entertainment devices such as DVD players have become readily available as options on many vehicles. In addition, with the increase in technology and advance of electronics manufacturing, the cost and size of portable entertainment devices such as portable DVD players have also become attractive. Accordingly, portable entertainment devices such as DVD players that can dock with vehicles have been designed and implemented. These systems provide the convenience of vehicle systems, such as vehicle integrated controls, vehicle sound system compatibility, and convenient viewing. In addition, the removable entertainment device may be readily removed from the vehicle and used elsewhere. However, the easy removal of the removable entertainment device may often leave such devices vulnerable to theft. Due to the high value and desirability of such players, a high theft rate may present an issue as to the long term viability of such products. In addition, theft may also be an issue for the vehicle manufacturer. Therefore, two theft scenarios must be addressed. First, the portable media device may be taken from a build and assembly plant and/or the dealership prior to vehicle installation or customer delivery. Second, the player may be stolen from the docking station in the vehicle after the consumer has purchased the vehicle. Although various docking mechanisms may be used to defeat removal of the player from the docking station, a more passive approach may be desirable and more convenient for the consumer.  
         [0005]     In view of the above, it is apparent that there exists a need for a system and method to provide passive anti-theft protection for a removable entertainment device.  
       SUMMARY  
       [0006]     In satisfying the above need, as well as overcoming the enumerated drawbacks and other limitations of the related art, the present invention provides a system and method to provide passive anti-theft protection for a removable entertainment device.  
         [0007]     The system includes a removable entertainment device that interfaces with a docking station. The removable entertainment device includes a controller that implements a software lock to disable the removable entertainment device, if it is improperly removed from the docking station. The docking station will use a challenge (seed) and response (key) message to provide a secure methodology to control the unlocking of the removable entertainment device.  
         [0008]     To address the protection of the removable entertainment device during production and shipment, the removable entertainment device is shipped in the anti-theft locked state of operation. In order for the removable entertainment device to be operated, it must first be docked into a valid docking station. The docking station sends a request for a seed to the removable entertainment device. In turn, the removable entertainment device responds with a seed, which is essentially a random number. Using the removable entertainment device supplied seed, the docking station will generate an algorithm dependent encrypted key. To complete the unlock sequence the docking station will issue an Unlock command, passing the encryption key as a parameter. The removable entertainment device then authenticates the key using the same algorithm and seed used to generate the key by the docking station. After authentication, the removable entertainment device enters an unlocked mode of operation. In the unlocked mode of operation, the removable entertainment device becomes fully functional. Otherwise, each time the removable entertainment device is powered up, it displays a “Player Locked” message for thirty seconds prior to entering its idle state of operation (off mode). It should be noted that both the removable entertainment device and docking station have re-try mechanisms. The re-try mechanisms may be used to ascertain the removable entertainment device mode (locked/unlocked), receive the encryption seed, validate the encrypted seed, and unlock the removable entertainment device. If the re-try mechanism fails, the “Authentication Failed” message is displayed, the docking station enters a shutdown state, and the removable entertainment device enters a display locked state. This is done to supply a degree of robustness, yet disallowing an unlimited number of retries which could ultimately lead to circumvention of the unlock procedure.  
         [0009]     To address the protection of the portable media device in the vehicle, each time the vehicle is powered down the docking station issues a lock enable command to the removable entertainment device. As long as the removable entertainment device remains docked, it will provide full user functionality allowing media playback using an internal battery, such as a Li-ion battery. If the removable entertainment device is removed from the docking station while in the lock-enabled state, the removable entertainment device will enter the anti-theft locked mode of operation and will prohibit user operation. As stated above, each time removable entertainment device is powered up, it will display the “Player Locked” message for thirty seconds before entering the shutdown state. To unlock the removable entertainment device and regain full user functionality the user must install the removable entertainment device into a valid docking station and apply full vehicle power to initiate the seed and key unlock procedure described above. The removable entertainment device is intended to be removed only when vehicle power is applied (i.e. the customers keys are in the ignition). Therefore, under normal usage the removable entertainment device would be in its unlocked state while being removed from the docking station. Therefore, under normal usage the removable entertainment device would never be undocked while in the lock enabled state.  
         [0010]     Further objects, features and advantages of this invention will become readily apparent to persons skilled in the art after a review of the following description, with reference to the drawings and claims that are appended to and form a part of this specification. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a perspective view of a removable entertainment device in accordance with the present invention;  
         [0012]      FIG. 2  is a schematic view of a removable entertainment device in accordance with the present invention;  
         [0013]      FIG. 3  is a flow chart illustrating a method to control release of the removable entertainment device in accordance with the present invention;  
         [0014]      FIG. 4  is a state transition diagram illustrating a method of passive anti-theft protection implemented by the docking station in accordance with the present invention; and  
         [0015]      FIG. 5  is a state transition diagram illustrating a method of passive anti-theft protection implemented by the removable entertainment device in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0016]      FIG. 1  illustrates a removable entertainment device, generally indicated in the figures at reference numeral  10 , in accordance with one embodiment of the present invention. The removable entertainment device  10  includes an information retrieval device  12 , a video display screen  14 , electronics  18 , a housing unit  20 , and at least one vehicle docking station  22 . The video display screen  14  is preferably pivotally mounted to the housing  20  such that the display screen  14  can be pivoted away from the housing  20  when viewing is desired and toward the housing  20  when storage of the screen  14  is desired. The vehicle docking station  22  releasably receives the housing unit  20 .  
         [0017]     The information retrieval device  12  is preferably a component that is capable of receiving a removable storage medium  24  and reading entertainment information stored on the medium  24 . Particularly preferable, the information retrieval device  12  comprises a component capable of receiving and reading a standard type of storage media. As illustrated in the figure, the information retrieval device  12  preferably comprises a DVD (digital video disk) drive. In this embodiment, the removable storage medium  24  comprises a DVD. Alternatively, the information retrieval device  12  can comprise a compact disk (CD) drive, a CD-ROM drive, a removable or fixed hard drive, a videocassette drive, or any other suitable component. The removable storage medium  24  will of course be appropriate for the type of information retrieval device  12  utilized.  
         [0018]     The video display screen  14  comprises the video output device of the removable entertainment device  10 . As such, the screen  14  displays images based on information contained on the removable storage medium  24  as read by the information retrieval device  12 . The type of video display screen  14  employed will depend on the desired resolution and picture quality. LCD screens, such as those used in portable computers and personal entertainment systems, are suitable.  
         [0019]     The electronics  18  are adapted to read the information stored on the removable storage medium  24  and to display an image based on this information onto the video display screen  14 . As such, suitable electronics  18  include those typically utilized in the type of information retrieval device  12  employed in the removable entertainment device  10 .  
         [0020]     The housing unit  20  contains the information retrieval device  12  and the electronics  18 . Preferably, the housing unit  20  encases the information retrieval device  12  and electronics  18  while still allowing the information retrieval device  12  to receive a removable storage medium  24  and the terminals of connector  34  to interact with external electrical components. Further, the housing unit  20  preferably mounts the video display screen  14  in a manner that allows the screen  14  to pivot between first and second positions. In the first position, the screen  14  is preferably positioned directly adjacent the housing  20  such that the image cannot be viewed on the screen. In a second position, the screen  14  is preferably positioned substantially perpendicular to the length of the housing  20  such that the image  26  can be optimally viewed. Any suitable structural interaction between the housing  20  and video display screen  14  that achieves this pivotal relationship can be utilized.  
         [0021]     The vehicle docking station  22  is able to releasably receive the housing unit  20 . The vehicle docking station  22  also preferably contains fasteners for attaching the bracket  22  to the vehicle, such as at the roof or ceiling of the vehicle. In addition, the vehicle docking station  22  preferably defines one or more electrical connectors  44  that are in electrical communication with at least a power supply  46  and, either directly or indirectly, one or more speakers  48  of the vehicle. Preferably, the electrical connector  44  comprises conductive flanges defined by the docking station  22 . Alternatively, the electrical connector  44  can comprise terminals of a pigtail connector or another suitable connector passed through an opening defined by the docking station  22 .  
         [0022]     Preferably, the electrical connector  44  is positioned such that it frictionally engages the terminals of connector  34  as the housing unit  20  is received by the vehicle docking station  22 . The electrical connector  44  and connector  34  are in electrical communication with each other, thereby placing the electronics  18  in electrical communication with the power supply  46  and vehicle audio system  48 , when the housing unit  20  is fully received by the vehicle docking station  22 .  
         [0023]     When the housing unit  20  is not seated in the vehicle docking station  22 , the removable entertainment device  10  is preferably capable of acting as a self contained entertainment device. Accordingly, the removable entertainment device  10  can further include an internal power supply  50  and an audio output component  52 . The internal power supply  50  can comprise any suitable power supply, such as a rechargeable battery. Also, the audio output component  52  can comprise any suitable audio output device, such as a wired ready jack or wireless headphone transmitter, an internal speaker, or a speaker jack.  
         [0024]     Now referring to  FIG. 2 , a schematic view of the removable entertainment device  10  and the docking station  22  are provided. The docking station  22  includes a controller  60  that monitors and controls operation of the docking station  22 . The controller  60  is in electrical communication with the removable entertainment device  10 . More specifically, the controller  60  is in electrical communication with a controller  54  configured to monitor and control operation of the removable entertainment device  10 . Controller  60  and controller  54  communicate control information across a status signal  58 . The status signal  58  may be communicated over a physical connection or using a wireless communication technology such as an infrared communication link. Accordingly, all of the input or output information from controller  60  may be made available to controller  54  and all of the input or output information of controller  54  may be made available to controller  60  over the status signal  58 . Controller  54  is located in the removable entertainment device  10  and is in electrical communication with the information retrieval device  12 . The controller  54  may manipulate the information retrieval device  12  to retract or eject media, as well as, access data therefrom.  
         [0025]     The removable entertainment device  10  is connected to the docking station  22  through electrical connector  34  and electrical connector  44 . Accordingly, the removable entertainment device  10  is connected to a power supply  46  in the docking station  22 . The power supply  46  may provide power for operation of the removable entertainment device  10 , as well as charging of the internal power supply  50 . The power sensor  55  is in electrical communication with the power supply  46  and may provide a signal to the controller  54  when the power supply  46  is disconnected from the removable entertainment device  10 . In a similar fashion, a player present sensor  59  is in communication with a player present circuit of the docking station  22  and provides a signal to the controller  54  when the player present circuit is disconnected from the portable media device  10 . The removable entertainment device  10  includes a screen closure sensor  56  and a movement sensor  57  in electrical communication with the controller  54 .  
         [0026]     The controller  60  includes a player power output  62  which is connected to a first end of resistor  64 . The other end of resistor  64  is connected to the removable entertainment device  10  through node  65 . Node  65  is connected to a power source  66  through a pull up resistor  68 . A player present input  70  of the controller  60  is also in communication with node  65 . Accordingly, if the removable entertainment device  10  is not connected to the docking station  22 , the player present input  70  is pulled high by the power source  66 . Alternatively, when the removable entertainment device  10  is present, node  65  is pulled to a reference voltage, such as ground  74  through the removable entertainment device  10 . Node  65  is connected to the ground  74  along a ground loop  72  in the removable entertainment device  10  that is accessed through connectors  34  and  44 .  
         [0027]     In addition, the controller  60  includes a player supported input  76 . The player supported input  76  detects whether pressure is being applied to the removable entertainment device  10 . If the removable entertainment device  10  is received into the bottom of the docking station  22  as shown in  FIG. 1 , the removable entertainment device  10  will need to be supported when released by the docking station  22  to prevent dropping of the removable entertainment device  10 . Support can be provided by an occupant pushing upward on the removable entertainment device  10  prior to release by the docking station  22 . This support may be measured by a pressure sensor  82 , such as a pressure sensitive switch interfaced with the removable entertainment device  10 . The player supported input  76  is connected to a power source  78  through a pull up resistor  80 . The player supported input  76  is also connected to the pressure sensor  82  in the removable entertainment device  10  through connectors  34  and  44 . If pressure is applied to the removable entertainment device  10 , the pressure sensor  82  connects the player supported input  76  to a reference voltage, such as ground  84 . In addition, the pressure sensor  82  is in electrical communication with the controller  54  allowing the information retrieval device  12  to retract the removable storage media  24  based on a signal from the pressure sensor  82 .  
         [0028]     To control whether the removable entertainment device  10  is latched into the docking station  22 , a solenoid enable output  88  is provided. The solenoid enable output  88  controls a solenoid  90 , thereby moving a pin  91 . The pin  91  is biased to engage a latch  86  preventing movement of the latch  86 . The latch  86  engages the removable entertainment device  10  preventing it from being released by the docking station  22 . The solenoid enable output  88  is configured to activate the solenoid  90  thereby disengaging the pin  91  and allowing movement of the latch  86  when the removable entertainment device  10  is supported. For example, the controller  60  may check the player supported input  76  to determine if the removable entertainment device  10  is supported prior to allowing movement of the latch  86 . Accordingly, the removable entertainment device  10  will not be released from the docking station  22  unless sufficient support is provided to prevent the removable entertainment device  10  from falling. A player locked input  92  is also provided by the controller  60 . The player locked input  92  is connected to a player locked sensor  94  such as a switch. The player locked sensor  94  is configured to determine if the latch  86  is in the locked position. If the latch  86  is not in the locked position, the player locked sensor  94  connects a voltage source  96  to the player locked input  92  to inform the controller  60  that the latch  86  has been moved to the unlocked position thereby releasing the removable entertainment device  10  from the docking station  22 .  
         [0029]     In addition, the controller  60  includes optical alarm output  96  connected to an illumination device such as a LED  97 . The controller may activate the optical alarm output  96  causing blinking of the LED  97  based on an error condition perceived by the controller  60 . The error condition may include such things as the player locked sensor  94  indicating the latch  86  is in an unlocked position when the player supported input  76  indicates the removable entertainment device  10  is not supported.  
         [0030]     Now referring to  FIG. 3 , a method  100  for releasing the removable entertainment device  10  from the docking station  22  is provided. In block  102 , the controller  60  determines if the vehicle is in idle or full power mode, the player power output  62  is asserted as denoted by block  104 . In block  106 , the controller  60  determines if the removable entertainment device  10  is present based on the player present input  70 . The player present input  70  may be monitored by the controller  60  via a polling routine or through an interrupt driven request. If the player is not present, the logic follows line  108  and loops back to block  106  until the player is present. When the player is present, the logic follows line  110  to block  112 . In block  112 , the controller  60  determines whether a one second delay has been met. If a one second delay has not been met, the logic follows line  114  back to block  112  until the delay has been met. The controller  60  may provide the capability to configure any of the delays within a range, for example, between one and ten seconds. If the delay is met, the logic flows along line  116  to block  118 .  
         [0031]     In block  118 , the controller  60  determines whether the player is supported via the player supported input  76 . If the removable entertainment device  10  is not supported, the logic follows along line  120  and the controller  60  determines if the removable entertainment device  10  is present as denoted by block  122 . The controller  60  determines if the removable entertainment device  10  is present based on the player present input  70 . If the player is not present, the logic flows along line  126  back to block  106  where the method  100  loops until the removable entertainment device  10  becomes present. If the logic in block  122  determines the removable entertainment device  10  is present, the logic flows along line  124  back to block  118 , thereby forming a loop until the removable entertainment device  10  is supported. If the removable entertainment device  10  is supported, the logic flows along line  128  to block  130 .  
         [0032]     In block  130 , the controller  60  determines whether the information retrieval device  12  is currently ejecting or if the removable storage medium  24  is in the slot of the information retrieval device  12 . If the information retrieval device  12  is ejecting or the removable storage medium  24  is in the slot, the logic flows along line  132  to block  134 . In block  134 , a load command is issued to the information retrieval device  12  to retract the removable storage medium  24  into the information retrieval device  12 . Thereafter, logic flows along line  136  to block  118 . Alternatively, if the information retrieval device  12  is not ejecting and the removable storage medium  24  is not in the slot as determined by block  130 , the logic flows along line  138 .  
         [0033]     In block  140 , the controller  60  asserts the solenoid enable output  88  and activates a chime indicating the removable entertainment device  10  is ready to be removed. In block  142 , the controller  60  determines if a five second delay has been met or if the removable entertainment device  10  is not present as determined by the player present input  70 . If the timed delay has not been met and the removable entertainment device  10  is present, the logic flows along line  144  back to block  142 . The delay is to limit the “on time” of the solenoid  90  to reduce heating caused by continuous solenoid operation. If the delay is met or the removable entertainment device  10  is no longer present, the logic flows along line  146  to block  148 .  
         [0034]     In block  148 , the controller  60  de-asserts the solenoid enable output  88  and deactivates the remove chime. In block  150 , the controller  60  determines whether a delay time has been met. If the delay time has not been met, the logic flows along  152  back to block  150  until the timed delay has been met. The timed delay is provided to allow cooling of the solenoid between cycles. When the timed delay has been met in block  150 , logic flows along line  154  back to block  106  where the method is continued.  
         [0035]     Now referring to  FIG. 4 , a method  200  is illustrated in a state transition diagram for the docking station anti-theft system. The state transition diagram uses UML notation. Accordingly, transitions are of the form Event [Guard Condition]/Action. Event is interpreted as an occurrence or edge trigger that causes evaluation of the Guard Condition. Guard Condition is a level test. Action is the work performed if the transition is taken (i.e. the Event occurred and the Guard Condition was true). If the condition(s) shown are met (items before the “I”) the Action(s) are performed and the state transitions to the next state as indicated by the arrow. Table 1 is provided below to aid in interpretation of the signals used by the state transition diagram.  
                             TABLE 1                           Docking Station Signal Description            Signal   Type   Description               Wakeup   Event   The module is awakened from a low or no power state       Player Docked   Event   The player has become docked       Apply Power to   Action   The docking station applied VBATT to player.       Player       Shutdown   Event   The module is commanded to enter a low or no power state       Lock Player   Action   The docking station sends the Lock Enable Message over the               Status Signal (58) to the player       Remove Power to   Action   The docking station removes power from the VBATT of the player       Player       Player Unlocked   Event   The player has responded with status that it is unlocked       Player Locked   Event   The player has responded with status that it is locked       Query Player   Action   The docking station sends the Lock Status Request message to the       Lock Status       player over the status signal (58)       Request   Action   The docking station requests the random seed from the player over       Challenge       the status signal (58)       Challenge   Event   The player sends the random seed to the docking station over the               status signal (58)       Response with   Action   The docking station encrypts the random seed using the private key       Encrypted       and sends the encrypted result to the player over the status signal       Challenge       (58)       Player not   Guard   A level test to see if the player is currently not docked       Docked   Condition       Player Docked   Guard   A level test to see if the player is currently docked           Condition                  
 
         [0036]     The software lock described ensures that theft or any other form of invalid removal of the removable entertainment device  10  will render the device inoperable.  
         [0037]     From any of the states when the docking station  22  is shut down, a signal is sent to the portable entertainment media device  10  to lock the removable entertainment device  10  and remove power, as indicated by line  201 . Accordingly, the method  200  to enter the OFF state as denoted by block  202 . When the docking station wakes up and the removable entertainment device  10  is docked, the controller  60  applies power to the removable entertainment device  10  as denoted by line  204  and transitions to the challenge response state in block  210 .  
         [0038]     The challenge response state  210  is initialized as denoted by line  220 . During initialization, the player locked status is queried, the number of retries is set to a predetermined number such as four, and the timer is set to a predetermined timeout value. After initialization, the logic enters block  212  waiting for player status. If the removable entertainment device  10  is locked the controller  60  requests a challenge as noted by line  214  thereby switching the method  200  into the waiting for player challenge state as noted by block  216 . If a challenge (seed) is provided from the removable entertainment device  10 , the docking station  22  responds with an encrypted challenge (key) as noted by line  218  allowing the controller  60  to enter the waiting for player status state as noted by block  212 .  
         [0039]     If the encrypted challenge is correct, the removable entertainment device  10  is unlocked as denoted by line  222  and the docking station  22  enters a normal application state as denoted by block  224 . However, if no retries are left, or the challenge response state reaches a time-out, the method  210  flows along line  232  and enters a rear seat control state as denoted by block  228 . In the rear seat controller state, the docking station  22  provides auxiliary controls for accessories other than the removable entertainment device  10 , such as radio controls or climate controls.  
         [0040]     If the docking station  22  is in the OFF state  202  and the docking station  22  wakes up, however, the removable entertainment device  10  is not docked, the player power is enabled as denoted by line  226 . Following line  226 , the method  200  directly enters the rear seat controller state in block  228 . When the removable entertainment device  10  is docked as denoted by line  230 , the docking station  22  enters the challenge response state  210  to verify the removable entertainment device  10  is docked using the seed/key scenario as described above.  
         [0041]     Now referring to  FIG. 5 , a method  300  is illustrated in a state transition diagram for controlling the removable entertainment device  10 . To aid in the interpretation of the signals used in the state transition diagram Table 2 is provided below.  
                             TABLE 2                           Player Signal Description            Signal   Type   Description               Wakeup   Event   The module is awakened from a low or no power state       Locked   Guard   Returns true if the Player is locked           Condition       Docked   Guard   Returns true if the Player is currently installed in the docking station           Condition       Unlocked   Guard   Returns true if the Player is currently not locked           Condition       Undocked   Guard   Returns true if the Player is currently not installed in the docking           Condition   station       Powered   Guard   Returns true if power is currently applied to the VBATT and Status           Condition   Signal (58)       Unpowered   Guard   Returns true if power is not currently applied to the VBATT and           Condition   Status Signal (58)       Anti-theft   Guard   Returns true if the Player is currently locked due to a theft attempt           Condition       Powered   Event   Power has just been applied to VBATT and Status Signal (58)       Docked   Event   The Player has just been installed into the docking station       Locked   Event   The Player has just been locked       Request   Event   The docking station has just sent the request for the random seed               over the Status Signal (58)       Response   Event   The docking station has just sent the encrypted random seed over               the Status Signal (58)       Decryption   Event   The decrypted docking station response matches the original       OK       random seed       Send   Action   The Player sends the random seed to the docking station over the       Challenge       Status Signal (58)       Decrypt   Action   The Player decrypts the docking station&#39;s response using the               private Key       Clear Anti-   Action   Clears the Anti-theft flag       Theft       Lock   Event   The docking station sent the Lock Enable message over the Status       Command       Signal (58)       Ready to   Guard   The player is allowed to lock       Lock   Condition       Lock Status   Event   The docking station sends the Lock Status Request message to the       Request       player over the Status Signal (58)       Send Player   Action   The player sends the Player Locked status message to the docking       Locked       station over the Status Signal (58)       Send Player   Action   The players sends the Player Unlocked status message to the       Unlocked       docking station over the Status Signal (58)       Shutdown   Event   The player is commanded to enter a low or no power state       Shutdown   Action   Issue the Shutdown event                  
 
         [0042]     As denoted by line  301 , shut down from any of the other state transitions method  300  into the OFF state as denoted by block  302 . When the removable entertainment device  10  wakes up and is unlocked as denoted by line  304 , the removable entertainment device  10  transitions the normal application state as denoted by block  306 . Similarly, when the removable entertainment device  10  wakes up and is locked, docked, unpowered, and the anti-theft is not active as denoted by line  308 , the removable entertainment device  10  also enters the normal application state  306 . If the removable entertainment device  10  wakes up and the removable entertainment device  10  is locked, docked, and powered as denoted by line  310 , the removable entertainment device  10  enters the challenge response state as denoted by block  312 .  
         [0043]     The challenge response state is initialized as denoted by line  328 . During initialization, an authenticating message is rendered on the display, the number of retries is set to three, and a timer is set. The removable entertainment device  10  enters the waiting for challenge request state as denoted by block  314 . A request to send challenge, including a seed, is then provided to the docking station  22  as denoted by line  316 . Accordingly, the portable media player enters the waiting for response state as denoted by block  318 . A response, including a key, is received and decrypted as denoted by line  320  allowing the removable entertainment device  10  to enter the decide unlock state  322 . If the decryption is correct, the removable entertainment device  10  is unlocked, the anti-theft flag is cleared as denoted by line  324  allowing the removable entertainment device  10  to enter the normal application state  306 . If the decryption is not correct, the removable entertainment device  10  is set to locked and the number of retires is decremented as denoted by line  326 . This causes the removable entertainment device  10  to enter the waiting for challenge request state  314 . Accordingly, the request to send challenge may be resent until no retries are left or the challenge response state times out. If no retries are left or the challenge response state times out, an authentication failed message is rendered on the display and the anti-theft flag is set as denoted by line  340 . After the anti-theft flag is set, the removable entertainment device  10  enters the lock display state in block  334 .  
         [0044]     In addition, if the removable entertainment device  10  wakes up in a locked and undocked state, a locked message is rendered on the display and the anti-theft flag is set as denoted by line  330  causing the removable entertainment device  10  to enter the locked display state  334 . Similarly, if the removable entertainment device  10  wakes up locked and undocked and unpowered and the anti-theft flag is set, then a locked message is rendered on the display as indicated by line  332 . The removable entertainment device  10  again enters the locked display state  334 .  
         [0045]     While in the locked display state  334 , if the removable entertainment device  10  is powered while the portable media entertainment  10  is docked as indicated by line  336 , the removable entertainment device  10  enters the challenge response state  312 . Similarly, if the removable entertainment device  10  is docked while it is powered, as indicated by line  338 , the removable entertainment device  10  also enters the challenge response state  312 . As indicated by line  342 , if the portable medial entertainment device  10  is locked and undocked, the locked message is rendered on the display and the anti-theft flag is set causing the portable medial entertainment device  10  to enter the locked display stated  334 . Further, as noted by line  344 , thirty seconds after entering the locked display state  334 , the removable entertainment device  10  shuts down which will transition the removable entertainment device to line  301 , thereby entering the OFF state  302 .  
         [0046]     As a person skilled in the art will readily appreciate, the above description is meant as an illustration of implementation of the principles this invention. This description is not intended to limit the scope or application of this invention in that the invention is susceptible to modification, variation and change, without departing from the spirit of this invention, as defined in the following claims.
The system includes a removable entertainment device that interfaces with a docking station. The removable entertainment device includes a controller that implements a software lock to disable the removable entertainment device, if it is improperly removed from the docking station. The docking station uses a challenge and response message to provide a secure methodology to control the unlocking of the removable entertainment device.