Abstract:
A computer, or other electrical component, having an electrical switch adapted to open when the cover of the chassis of the component covers the chassis and close when the cover is removed from the chassis. A mechanism is provided that turns on, and stays turned on, in response to the closing of the switch for providing an output. An indication device is connected to the mechanism and is adapted to provide a corresponding indication when the mechanism turns on.

Description:
BACKGROUND 
     This disclosure relates to a computer and, more particularly, to a computer provided with a detector that detects intrusion into the interior of the computer and provides an indication of same. 
     It is often desirable, for security and other reasons, for the owner, or user, of a computer, to know if someone has accessed the interior of his computer. For example, in network systems including a large number of desktop computers, various components in the chassis of the computers often have to be replaced by the systems manager. In these situations, it is desirable that the user of the computer know that someone has accessed his or her computer and made the replacements. 
     Also, since valuable, sensitive, and secret data can be removed from the computer by physically removing the hard drive from the computer, it is important that the user also know when an intrusion of this type has taken place. 
     SUMMARY 
     Therefore, the present disclosure is directed to a computer having a detector for detecting an intrusion into the chassis of the computer. 
     To this end, an embodiment of the present invention features an electrical switch adapted to open when the cover of the chassis of the computer covers the chassis and close when the cover is removed from the chassis. A mechanism is provided that turns on in response to the closing of the switch for providing an output, and an indication device is connected to the mechanism and is adapted to provide a corresponding indication when the mechanism turns on. 
     The embodiment provides an advantage of indicating chassis intrusion in a relatively simple manner, yet prevents overriding or clearing of an intrusion event. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic view of a computer according to an embodiment of the present invention. 
     FIG. 2 is a isometric view of the embodiment of FIG. 1 
     FIG. 3 is a view similar to that of FIG. 1, but depicting the embodiment of FIG. 1 with its cover in a position slightly above its normal position. 
     FIG. 4 is a schematic view of an intrusion indicator circuit of the embodiment of FIGS.  1 - 3 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 depicts a personal computer, shown in general by the reference numeral  10 , which can be in the form of a desktop computer, a laptop computer or a tower computer. The computer  10  includes a chassis  12  in which a motherboard  14  is mounted. A processor  16 , a plurality of memory devices or modules  18 , and two input/output (I/O) devices  20  are mounted on the motherboard  14 . Two buses  16   a  and  16   b  are also provided on the motherboard  14  and connect the processor  16  to the memory modules  18  and to the input/output devices  20 , respectively. A power supply  22  is connected to the motherboard  14 , and a pair of cable assemblies  24   a  and  24   b  connect the motherboard to a hard drive unit  26  and a disk drive unit  28 , respectively. It is understood that other components, electrical traces, electrical circuits and related devices (not shown) are provided in the chassis  12 . Since these are all conventional, they will not be described in any further detail. 
     With reference to FIGS. 2 and 3, a cover  30  extends over the chassis  12  of the computer  10 . The cover  30  is conventional, and as such, has a front wall  32  and a side wall  34 . Although not shown in the drawing, it is understood that the cover  30  also includes another side wall, opposite the side wall  34 , and a rear wall. 
     Two openings  32   a  and  32   b  are provided through the front wall  32  for receiving drive units, such as a floppy disc drive, and a CD ROM drive. A push button  36  is also provided on the front wall  32  for turning the computer  10  on and off. 
     As shown in FIG. 3, a switch  40  is mounted on a side wall of the chassis  12  and is adapted to be engaged by the side wall  34  of the cover  30  when the cover is completely mounted over the chassis as shown in FIG.  2 . The switch  40  is in the form of a mechanical momentary switch of a conventional design and is connected in an intrusion detector circuit shown in FIG.  4 . 
     With reference to FIG. 4, the latter circuit also includes a flip-flop latch mechanism  42  electrically connected to the switch  40 , via a conductor  44 . A display  46 , for indicating chassis intrusion, is electrically connected to an output of the latch mechanism  42 . The circuit of FIG. 4 is connected to the power supply  22  (FIG. 1) of the computer  10  and the latch mechanism  42  is designed to attain an off, or inactive, state when a relatively high voltage, or logic, level is present in the circuit. The latch mechanism is  42  also adapted to switch to an on, or active, state in response to this voltage level reducing to a relatively low level. Also, once the latch mechanism  42  attains an active state in response to the relatively low voltage, it will remain in its active state even if the voltage level later increases back to the relatively high level, for reasons to be explained. 
     A battery  50  is connected to the latch mechanism  42  to power same independently of, and as an alternate to, the power supply  22 . An RC circuit, including a resistor  52  and a capacitor  54  connected in series, is connected in the circuit of FIG. 4 between the battery  50  and ground, and to the conductor  44 . 
     A display  56  is also connected to the conductor  44  and can include a counter for providing and displaying the number of times the cover  30  has been removed from the chassis  12  and the elapsed time since the last time the cover has been removed. 
     It is understood that the circuit shown in FIG. 4 can be mounted in the chassis  12  and can be provided on a circuit board or the like, in a conventional manner, and that the displays  46  and  56  can be mechanically connected to the chassis  12  or to a separate, stand alone, display device (not shown). 
     In operation, the switch  40  is forced to a retracted, electrically-open position, shown by the dashed line in FIG. 4, by the cover  30  when the cover is assembled over the chassis  12  during normal use of the computer  10 , as shown in FIG.  2 . Since the circuit of FIG. 4 is electrically connected to the power supply  22  of the computer, a relatively high voltage will be normally be established in the circuit of FIG. 4 to maintain the latch mechanism in an inactive state, as discussed above. 
     However, when the cover  30  is removed from the chassis  12 , or, more specifically, when it is lifted from the chassis to a position exposing the switch  40 , the switch  40  spring biases to its extended, electrically-closed, position as shown by the solid line in FIG.  4 . This causes current to flow in the circuit of FIG.  4  through the resistor  52  and the switch  40  to reduce the voltage in the circuit to a predetermined, relatively low, level, such as zero. The latch mechanism  42  responds accordingly and switches to an “on”, or active, mode to activate the display  46  which provides a visual indication of chassis intrusion. This closing of the switch  40  also activates the display  56  which displays the number of times the cover  30  has been removed from the chassis  12  and the elapsed time since the removal. 
     When the cover is later replaced completely over the chassis  12  as shown in FIG. 2, the switch  40  is forced to a retracted, electrically open position, shown by the dashed line in FIG. 4, and the current flow through the switch is terminated. Although the voltage level across the latch mechanism  42  will thus go back to a relatively high value, the latch mechanism is designed to remain in its active, or on state, and the display  46  thus remains on. Therefore, a continuous visual indication of chassis intrusion is provided, notwithstanding replacement of the cover  30 . In this context, the opening of the switch  40  causes the display  56  to turn off since the display is directly connected to the switch  40 . 
     After the cover  30  is replaced over the chassis  12 , it is understood that the latch mechanism  42  is adapted to be manually reset by the user or system manager. For example, software can be loaded into the computer  10  which enables the user or manager to reset the latch mechanism  42  to its inactive, or off, position after entering a proper password, or the like. 
     The circuit of FIG. 4 is designed to prevent clearance of an intrusion event by removal of the AC power to the computer  10  after the cover  30  is removed from the chassis  12 . More particularly, if the AC power to the computer  10 , and therefore the current from the power supply  22  to the circuit of FIG. 4, is removed, the battery  50  will supply the requisite voltage to the circuit. Thus, the above operation, including that of the latch mechanism  42 , will not be interrupted or changed, even if the AC power is later restored to the computer  10 . 
     Also, an intrusion event will not be cleared even if the intruder takes additional steps to clear the intrusion. For example, after the cover  30  is removed, if the intruder then disconnects the AC power to the computer  10  and removes the battery  50  from the circuit of FIG. 4, the latch mechanism  42  will still remain in its active, or on state since there would be no current to increase the voltage in the circuit. If the cover  30  is replaced and the AC power is then restored and/or the battery  50  is reinstalled in the circuit, the voltage in the circuit of FIG. 4 would go back up to a relatively high level consistent with the latch mechanism  42  being in its off, or inactive, mode. However this does not happen since the circuit would take a few milliseconds to charge up to its relatively high voltage level due to the presence of the RC circuit, including the resistor  52  and the capacitor  54 . Therefore, immediately after the power is restored to the circuit and before the voltage in the circuit reaches the relatively high level, the latch mechanism  42  would respond to the relative low voltage level during the charging of the circuit and would therefore remain in its active, or on, state. Thus, the latch mechanism  42  would keep the display  46  on in the manner discussed above notwithstanding the fact that the voltage level in the circuit would increase to the relatively high value. This would also be true if the switch  40  is also disconnected from the motherboard  14  in a further attempt to clear an intrusion. 
     Thus, the circuit of FIG. 4 is easily installed in the computer  10  yet provides a reliable indication of chassis intrusion. Also, the circuit is designed to provide an indication of an intrusion event, despite the above efforts to clear the intrusion event. 
     It is understood that variations may be made in the foregoing without departing from the scope of the invention. For example, either one or both of the displays  46  and  56  can be adapted to provide an audible alarm either in place of, or in addition to, the visual display. Also, the switch  40  can be mounted on the cover  30 , rather than the chassis  12 . Further, the intrusion circuit of FIG. 4 is not limited to use with computers, but is equally applicable to other electronic components which lend themselves to intrusion detection. 
     Other modifications, changes and substitutions are intended in the foregoing disclosure and in some instances some features of the disclosure will be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the disclosure.