Patent Publication Number: US-4837819-A

Title: Security handset

Description:
This invention relates to secure telephone systems but more particularly to a security device for use with a telephone handset to prevent eavesdropping while the handset is in an on-hook position. 
     One of the requirements of secure telephone systems, is that eavesdropping or bugging of the telephone be prevented when the telephone handset is in an on-hook position. 
     It was determined that eavesdropping could still be achieved even though the handset is in an on-hook position. The ear and microphone transducers of the telephone handset could be used to pick up and monitor a conversation. 
     A telephone security device for preventing use of an on-hook telephone for eavesdropping or bugging is disclosed in U.S. Pat. No. 3,715,514 which issued to Alan D. Bell. With this device, a voltage source is connected to the telephone line selector and hook switch through a dialled matrix and sensing relay coil. When the telephone is on-hook (that is with the hook switch open) all conductors from the telephone instrument are short circuited together and are disconnected from the telephone conductors leading out of a private or secure area in which the telephone is located. The short circuiting is accomplished by a plurality of relays responsive to the condition of the sensing relay. When the telephone is off-hook the conductors leading from the telephone are connected to the conductors leading from the area for normal conversational use. A lamp and photoresistor device is provided to isolate the annunciator from external conductors. 
     The problems associated with this system is that the use of relay coils and a diode matrix in a circuit design results in a relatively bulky and complex device which can be difficult to install and expensive to manufacture. 
     There is therefore a requirement for a telephone security device which is simple to use, easy to manufacture and which can be readily installed within the handset. 
     Accordingly, a first object of the present invention is to provide a security device for use with a telephone handset and which is relatively easy to install and inexpensive to manufacture. 
     Another object of the present invention is to provide a security device able to place the telephone handset in either an operative or secure mode depending on the orientation of the telephone handset. 
     Yet another object of the present invention is to provide a security device adapted to be placed in a telephone handset and which will short circuit the microphone and ear transducers and disconnect them from the main set when the handset is in the secure mode. 
     Accordingly, an aspect of the present invention is to provide a security device for use with a telephone handset having a microphone and an ear transducer, adapted to prevent eavesdropping while the handset is in an on-hook position, comprising: switching means disposed in said handset adapted to disable said transducers, said switching means being switched to a first state when said handset is placed within a first range of predetermined orientations corresponding to a secure mode and said switching means being switched to a second state when said handset is placed within a second range of pedetermined orientations corresponding to an operative mode. 
    
    
     Particular embodiments of the invention will be understood in conjunction with the accompanying drawings in which: 
     FIG. 1 is a block diagram of the security device according to the preferred embodiment of the present invention; 
     FIGS. 2a to 2c illustrate the operational range of the security device when the telephone handset is in the secure mode; 
     FIG. 3 is a sectional view of the security device mounting block of the present invention, taken along lines 3--3 of FIG. 5; 
     FIG. 4 is a sectional view of the mounting block taken along lines 4--4 of FIG. 5; 
     FIG. 5 is a side view of the mounting block; 
     FIG. 6 is an illustrative view of a mercury switch used with the mounting block of FIG. 3; 
     FIG. 7 is a sectional view of a mercury switch receptacle taken along lines 7--7 of FIG. 4; 
     FIG. 8 is a sectional view of the mercury switch receptacle taken along lines 8--8 of FIG. 7; and 
     FIG. 9 is a perspective view of a mounting block according to the preferred embodiment of the present invention. 
    
    
     Referring now to FIG. 1, we have shown a block diagram of the security device according to the preferred embodiment of the present invention. 
     The security device is basically comprises of a number of position-sensing switches adapted to be disposed in a telephone handset (not shown). Depending on the orientation of the handset, the telephone is either in a secure mode or in an operative mode. As shown in FIG. 1, these position-sensing switches are connected to the ear transducer 11 and microphone transducer 12 forming part of a telephone handset (not shown). 
     A first pair of position sensing switches PSS 1  and PSS 2  is connected across ear transducer 11. A second pair of position sensing switches PSS 7  and PSS 8  is connected across microphone transducer 12. Each pair is so disposed in the handset, as will be described further, such that each switch is closed when the handset is within the first range of predetermined orientations, corresponding to the secure mode whereas at least one switch in each pair is open when the handset is within a second range of predetermined orientations corresponding to the operating mode. 
     A third pair of position sensing switches PSS 3  and PSS 4  is connected in series with terminal 18 of ear transducer 11. A fourth pair of position sensing switches PSS 5  and PSS 6  is connected in series with terminal 20 of ear transducer 11. 
     A fifth pair PSS 9  and PSS 10  is connected in series with terminal 23 of microphone transducer 12 and a sixth pair PSS 11  and PSS 12  is connected in series with terminal 24 of microphone transducer 12. 
     The third, fourth, fifth and sixth pair of position sensing switches are so disposed in the handset such that each switch is open when the handset is within the first range of predetermined orientations corresponding to the secure mode whereas at least one switch in each pair is closed when the handset is within the second range of predetermined orientation corresponding to the operating mode. 
     Referring no to FIGS. 2a to 2c, we have shown three series of movements which allows the secure device of the handset to change from a secure mode to an operating mode. The handset 30 is in a secure mode when the angle the longitudinal axis of the handset makes with the horizontal plane extends between 0 and a first predetermined angle. In FIG. 2a, the longitudinal axis of the handset is defined by a phantom line 32 which extends between the ear and microphone ends 33 and 34 respectively, of the handset 30. The horizontal plane is defined by line 31. Beyond this first predetermined angle, the handset should change from a secure mode to an operative mode. 
     Similarly, as shown in FIGS. 2b and 2c, the handset is within the first range of predetermined orientations corresponding to a secure mode, when the angle the lateral axis of the handset makes with the horizontal plane extends between 0 and a second predetermined angle. The lateral axis of the handset 30 is defined by a line extending perpendicular to the longitudinal axis and parallel to the horizontal plane. In FIG. 2b and 2c this lateral axis is illustrated at reference numeral 35. Beyond this second predetermined angle, the handset should change to an operative mode. 
     FIGS. 3 to 5 will be used to describe the position-sensing switch mounting block 40 which is adapted to retain each switch in a predetermined position and orientation. The mounting block is designed to be installed in the handset. The mounting block is generally rectangular and is defined by a top surface 41, a bottom surface 42, a first end 43, a second end 44, a first longitudinal side 45 and a second longitudinal side 46. 
     The mounting block is adpated to be installed in the telephone handset 30, see FIGS. 2a to 2c, with end 43 pointing towards the ear transducer 33 and end 44 pointing towards the microphone transducer 34. The top surface should face outwardly away from the transducers, i.e. facing the convex side of the handset. 
     The mounting block is provided with a plurality of receptacles a-f and a&#39;-f&#39; on each of said first and second longitudinal sides 45 and 46. Each is adpated to receive a position-sensing switch in a predetermined arrangement such that, in the secure mode, the first and second pair of position sensing switches will close to short circuit the ear and microphone transducers 11 and 12 respectively. The third, fourth, fifth and sixth pairs of switches will be open to disconnect these transducer from the main set (not shown). In the operating mode, at least one switch of each of the first and second pair will be open to remove the short across the transducers. At least one switch of each of the third, fourth, fifth and sixth pair will be closed to reconnect the transducers to the main set. 
     The receptacles are each generally tubular in shape and aligned generally along the same axis on each longitudinal side. Each receptacle slopes downwardly and are directed forwardly towards end 43 of block 40. The position-sensing switches are each inserted in a receptacle and interconnected as shown in FIGS. 3 and 4. 
     Each receptacle has a central axis A which makes an angle α (alpha) with the longitudinal axis B of the mounting block. Similarly, central axis A makes an angle β (Beta) with the lateral axis C of the mounting block. 
     The mercury switch 50 of FIG. 6 can be used as a position-sensing switch. In the preferred embodiment, the mercury switch should be provided with contact making terminals at one end. This allows the switch to be positioned in the receptacles so as to be either in the open or closed state. 
     The switch of FIG. 6 is generally tubular and has a first end 51 with a pair of terminals 52. 
     The first switch of each pair is inserted in a receptacle on the first longitudinal side of mounting block 40 and the second switch is inserted in a corresponding receptacle on the second longitudinal side of the mounting block. 
     For example, the position-sensing switches could be inserted in the mounting block receptacles as follows: 
     PSS 1  -a 
     PSS 2  -a&#39; 
     PSS 3  -b 
     PSS 4  -b&#39; 
     PSS 5  -c 
     PSS 6  -c&#39; 
     PSS 7  -d 
     PSS 8  -d&#39; 
     PSS 9  -e 
     PSS 10  -e&#39; 
     PSS 11  -f 
     PSS 12  -f&#39; 
     In the secure mode, position-sensing switches PSS 1 , PSS 2 , PSS 7  and PSS 8  should all be closed so as to short circuit the ear and microphone transducers 11 and 12 respectively. 
     Accordingly, each switch should be inserted in their respective receptacles with their contact making terminals pointing inwardly. 
     The remaining mercury switches forming each pair of the third, fourth, fifth and sixth pair of mercury switches are inserted in their respective receptacles with their contact making terminals pointing outwardly. These will accordingly be open when the handset is in the first predetermined orientation corresponding to the secure mode. 
     Accordingly, in operation, when the handset is pivoted about the microphone end of the handset as shown in FIG. 2a, each mercury switch will change state when the handset is moved within a second predetermined range of orientations. For example switches PSS 1 , PSS 2 , PSS 7  and PSS 8  will change from a closed state to an open one. This being caused by the movement of mercury from one end of the bulb where the contact terminals are located to the other end. Similarly, the remaining mercury switches will change from an open state to a close state where mercury will flow from one end of the bulb to the opposite end where the contact making terminals are located. 
     Similarly, when the handset is pivoted sideways, as shown in FIGS. 2b and 2c, the mercury switches located closest to the point of rotation will change state. For example, if the mounting block shown in FIGS. 3 and 4 is pivoted about the longitudinal side 46, the mercury switches on that side of the mounting block i.e. those in receptacles a&#39; to f&#39; will change state. Mercury will flow from the end of the switch pointing inwardly to the other end pointing outwardly. Switches PSS 2  and PSS 8  will change from a closed state to an open state. Switches PSS 4 , PSS 6 , PSS 10  and PSS 12  will change from an open state to a closed state. 
     With the change of state of switch PSS 2  and PSS 8 , the short across the ear and microphone transducers will be removed. Similarly, with the change of state of switch PSS 4 , PSS 6 , PSS 10  and PSS 12 , the terminals of each transducer will be reconnected. 
     Similarly, when the mounting block 40 is pivoted sideways about longitudinal side 45, the mercury switches in receptacles a to f will change state. 
     Referring now to FIG. 7, we have shown a sectional view of a receptacle used for retaining a mercury switch. Each receptacle is provided with a number of flexible ridges 60 secured at one end to the inner wall 61 of the receptacle. Each rib extends longitudinally along the length of the receptacle as can be more clearly shown in FIG. 8. 
     FIG. 8 is a sectional view of a receptacle taken along lone 8--8 of FIG. 7. When a mercury switch is inserted in a receptacle, the ribs 60 will flex to allow the bulb to be removably secured therein. This permits the proper positioning of a mercury bulb. 
     Referring now to FIG. 9, we have shown a mounting block according to a preferred embodiment of the present invention. The mounting block 70 is designed so as to be used with the MERIDIAN (trademark) type business set. The mounting block is slightly curved along the longitudinal axis in order to allow easy insertion in the handset. In addition, a series of grooves 71 and 72 allows the proper lining of leads running from a first mercury switch to another. In particular, these grooves are used for the leads interconnecting mercury switches PSS 1  to PSS 2  and switches PSS 7  and PSS 8 . 
     In the preferred embodiment, the angle α (alpha) the central axis A makes with the longitudinal axis B of the mounting block is 60°. The angle β (beta) the central axis A makes with the lateral axis C of the mounting block is 18°. 
     In the preferred embodiment, the handset will be in the secure mode (all connections from the handset cord to the microphone and ear transducers are open and a short is placed across the ear and microphone transducers) when the handset is laying on a flat table. Lifting the ear end of the handset up while maintaining table contact with the microphone end at any angle less than 9°, the secure mode will be maintained (see FIG. 2a). The operational mode (all transducers connect to the handset card and all shorts removed) must occur in the range of 9° to 52°. The operational mode must be maintained at any angle greater than 52°. 
     Similarly, while holding the left side of the handset on the table and lifting the right side (see FIG. 2b), the secure mode must be maintained at angles below 11°. The switch from secure to operational mode will occur in the range of 11° to 37°. The operational mode must be maintained at angles greater than 37°. The same angles for switching will apply for lifting the left side of the handset while holding the right side.