with reference to fig1 and 2 , an exemplary casing 1 is illustrated , comprising the anti - intrusion device according to the invention . the casing 1 comprises a cap 10 , a display screen 20 , an electronic card 3 and a flexible membrane 40 . the cap 10 consists of a top cap portion 101 and of a lower cap portion 102 . the display screen 20 is attached to the upper cap portion 101 . the electronic card 30 is a printed circuit comprising processing means and distinct interlaced electrically conducting contacts 31 intended to face keys of the flexible membrane 40 being used as entry means . these contacts 31 are for example made in metal . the electrically conducting contacts 31 are connected to processing means 34 , for example of the microprocessor type . the flexible membrane 40 is for example made in silicone or polyurethane . this membrane 40 comprises molded keys 41 , each key 41 corresponding to a portion of the membrane connected to the remainder of the membrane through a peripheral lip 42 . each key 41 crosses the upper cap portion 101 through an aperture 13 of the latter so as to be accessible from the outside . each key 41 comprises an electrically conducting portion 43 on its face facing the electronic card 30 . each key 41 is positioned facing both electrically conducting contacts 31 . according to the standard operating mode of a membrane keyboard , by pressing on a key 41 of the keyboard , the corresponding electrically conducting portion 43 may be connected with both underlying contacts 31 so as to close an electric circuit on the electronic card 30 . this closure is detected by the processing means which store in a memory the value corresponding to the pressed key . the casing 1 includes an anti - intrusion device comprising at least one mobile component 44 . this mobile component is a false key 44 provided at the membrane 40 and which is not visible from the outside of the casing 1 . the false key 44 is , similarly to the keys 41 , connected to the remainder of the membrane 40 by a peripheral lip 42 and comprises a protection circuit 45 positioned facing both electrically conducting terminals 32 , 33 and connecting the electrically conducting terminals 32 , 33 so as to close an electric circuit ( designated as the closed electric circuit hereafter ) in a normal position of use of the casing , i . e . when the upper cap portion 101 is attached to the lower cap portion 102 . the protection circuit will be described in more detail subsequently . both electrically conducting terminals 32 , 33 of the electronic card are positioned facing each other under the false key 44 . both electrically conducting terminals 32 , 33 form two portions of a security line connected to the processing means 34 . the processing means 34 are adapted in order to determine whether both electrically conducting terminals 32 , 33 are electrically connected , for example by measuring the resistance between the terminals of the security line . when an individual attempts to access the contents of the casing 1 , by removing the upper cap portion 101 , the false key 44 is no longer actuated by the upper cap portion 101 and is brought back by the action of the lip 42 towards a rest position in which the electrically conducting protection circuit 45 is no longer in contact with the electrically conducting terminals 32 , 33 . the processing means detect a change in the resistance of the security line , indicating that an attempt to open the device 10 is taking place , and apply anti - fraud functions of the casing , such as for example the shutdown of the casing 1 or further deletion of confidential data stored in a memory of the casing 1 . with reference to fig3 , an embodiment of the protection circuit 45 is illustrated . the protection circuit 45 comprises connection tracks 451 , a substrate 453 and suitable means for ensuring the opening of the closed electric circuit . the suitable means for ensuring the opening of the closed electric circuit enable the closed electric circuit to be opened in response to deterioration of the protection circuit ( by piercing , cutting , etc . ); or enable a resistance change to be detected due to a change in the pressure force exerted by the casing . thus , with the suitable means , the failure of an electric contact may be detected , either by displacement of the device by its mobility , or by opening by deterioration of the protection circuit . the suitable means comprise at least one electrically conducting track 452 . in the embodiment illustrated in fig3 and 4 , the electrically conducting track 452 is positioned inside the substrate 453 . with this , industrial scale production of the protection circuit 45 may be facilitated . moreover , the protection circuit 45 may also be adapted on the existing casing comprising a false key 44 such as the casings described in document fr 2 815 733 by attaching with clips the protection circuit at the base of the false key . the electrically conducting track 452 may be made in copper with a very fine pitch , industrially . the electrically conducting track 452 is positioned so as to be severed during an intrusion by piercing or cutting at the false key . more specifically , the width of the electrically conducting track 452 and the distance separating two adjacent portions of the track 452 ( no protective mesh ) are provided so as to be sufficiently narrow for inducing severing of the conducting track 452 upon an intrusion by piercing or cutting . diameter of the protection circuit = 10 millimeters , height of the protection circuit = 0 . 25 millimeters , width of the protection track = 0 . 15 millimeters , pitch of the mesh less than 1 millimeter , preferentially less than 0 . 5 millimeters , and even more preferentially about equal to 0 . 3 millimeters . materials used for forming the protection circuit : substrate : epoxy or polyethylene naphthalate ( pen ), tracks of the mesh : copper , connection tracks : carbon or silver or gold . advantageously , this exemplary protection circuit may be used with a false key with a diameter of 6 millimeters . in one embodiment , the electrically conducting track 452 is a track in the shape of a mesh . by & lt ;& lt ; mesh & gt ;& gt ;, within the scope of the present invention , is meant a rectangular wave pattern as illustrated in fig3 , or a spiral pattern . moreover , the mesh may be two - dimensional ( 2d ) or three - dimensional ( such as for example a grid pattern of the tennis racket type ). finally , the mesh may be made over several layers separated by an additional substrate thickness . the connection tracks 451 are positioned on one of the faces of the substrate 453 . in the embodiment illustrated in fig3 and 4 , the connection tracks 451 are two in number . the connection tracks 451 extend in a plane p 1 distinct from a plane p 2 in which the electrically conducting track 452 extends . the planes p 1 and p 2 are electrically insulated ( by an insulator 455 ), except in the area where the bridges 454 are found . both connection tracks 451 are connected to the electrically conducting track 452 through at least two electrically conducting bridges 454 illustrated in fig4 . the fact that the connection tracks 451 and the electrically conducting track 452 extend in distinct planes ensures a failure of the closed electric circuit regardless of the area of the protection circuit 45 in which piercing or cutting is accomplished . in certain embodiments , the connection tracks 451 are positioned in a central region of the substrate 453 . the difficulty of short - circuiting the protection circuit 45 may thereby be increased . both connection tracks 451 are intended to respectively come into contact with one of the two connection terminals 32 , 33 , positioned on the electronic card 30 . in one embodiment , the substrate 453 comprises an opaque layer . thus , the electrically conducting track 452 positioned inside the substrate 453 is not visible from the outside . also , the position of the connection tracks 451 is not visible from the outside when the protection circuit 45 is in place . with this it is possible to increase the difficulty for a malevolent third party to short - circuit the protection circuit 45 . in one embodiment , the substrate 453 covers a more extended surface area than the region in which the electrically conducting terminals 32 , 33 are found . it is thus possible to protect a more extended area of the electronic card than the false key 44 . in one embodiment , the substrate 453 is a flexible substrate which covers the whole surface of the electronic card 30 and is adhesively bonded onto the electronic card . in this case , the connection tracks 451 are for example made in carbon in order to ensure tearing off of the connection tracks 451 upon an attempt to detach the flexible substrate 453 . in the embodiment illustrated in fig4 , the protection circuit comprises 4 layers of different components : the epoxy substrate 453 , the copper mesh 452 , a layer of insulating varnish comprising two recesses so that the varnish layer does not cover the layer comprising the copper mesh at said recesses , a carbon ink layer deposited at the recesses by screen printing so that the carbon communicates with the layer of copper mesh : these communications form the bridges 454 . in one embodiment illustrated in fig5 , the electrically conducting terminals 32 , 33 have a symmetry of revolution . in this case , and as illustrated in fig6 , the connection tracks 451 are adapted to the shape of the electrically conducting terminals 32 , 33 so that one of the connection tracks comes into contact with one of the connection terminal 32 , and the other of the connection tracks 451 is in contact with the other one of the connection terminals 33 . with this , bringing the electrically conducting terminals 32 , 33 in contact with the connection tracks 451 may be facilitated , regardless of the orientation of the device . the reader will have understood that many changes may be provided without materially departing from the novel teachings and advantages described herein . for example , the protection circuit 45 may not comprise any substrate , the electrically conducting track 452 being in this case , positioned inside the flexible membrane 40 comprising the keys , and the connection tracks being positioned on the face of the membrane facing the electronic card , facing the connection terminals . finally , although the anti - intrusion device according to the invention has been described in the case of a casing on which a user enters confidential data , the present invention may also be applied in terminals which do not have input means but in which confidential information is stored . in this case , detection by the processing means of the opening of the terminal for example causes deletion of the confidential data stored in this terminal . the false key may be alone and dissociated from a keyboard membrane , in order to provide the same function for protecting an electronic casing , in the case when the latter does not include any keyboard or for detecting the opening of the lower portion of the casing . 32 , 33 electrically conducting terminals of the false keys ,