we describe a system and method for gathering dynamic presence information . according to an embodiment of the present invention , a mobile communications device gathers data about its surroundings to automatically determine the presence of potential eavesdroppers . we do not preclude individuals from manually providing information about their surroundings , nor do we preclude the use of information from other peoples &# 39 ; use of services such as cellular phone or wireless lan networks , or their wearing of badges ; but neither do we rely exclusively on such sources of location information . according to an embodiment of the present invention , we employ sensors as a part of , or an accessory to , the presentity &# 39 ; s communication device . these sensors detect characteristics of the physical environment surrounding the presentity ( presence information ). we define presence as an availability of the presentity for communication purposes . it indicates the communication state of the presentity . for example , presence information might encompass the physical proximity of the presentity to a speaker , or it might deal with non - physical proximity , such as the communication range of the presentity vis - à - vis the speaker . a presentity may be considered “ present ” for a communication while not actually being in close physical proximity to a speaker . this is because a presentity may employ communication devices which pick up long range transmissions . a mobile communications device ( such as a cell phone , pda , or laptop computer ) includes one or more means for determining the presence or absence of potential eavesdroppers and reporting this information to the potential participants in a communication . these means may include sensors to collect raw information and analytical mechanisms to compare sensor data . the analytical mechanisms may be implemented as computer programs running on processors embedded in either the mobile communications device or the sensors themselves . they compare sensor data to profiles of the sensor data expected when other people are present , or the analytical mechanisms may analyze combinations of data from multiple sensors to deduce the presence or absence of potential eavesdroppers . the sensors may include , for example , radio - frequency receivers that read active badges or passive rfid tags , or detect the presence of wireless lan , bluetooth , or cellular phone transmissions ; microwave , infrared , camera , or ultrasound systems to detect the presence , distance , contours , or motion of objects ; infrared systems to detect body heat ; microphones to detect ambient noise . a sensor may be embedded in the mobile communications device or mounted on a nearby support , such as a wall or a pole , communicating with the mobile communications device by bluetooth wireless technology or some other means . the sensors may be supplemented by human input , through some sort of a human - computer interface , conveying an individual &# 39 ; s own assessment of his or her surroundings , possibly including the presence , identity , and activities , and threat level of other individuals . this human input may be initiated by the individual supplying it , or supplied in response to a request from another party to the conversation , either before or during the conversation . referring to fig1 , consider a communication 100 among a first party 110 and one or more second parties 120 , 130 . possible forms of the communication include , but are not limited to , electronic mail , cellular telephone , instant message , and audio - video presentation . before sending sensitive information to a second party 130 , the first party 110 may wish to ascertain whether there are potential eavesdroppers 140 who may see , overhear , or intercept the communication to the second party 130 . referring to fig2 , there is shown a system 200 for providing a first party 110 with information about the potential presence of eavesdroppers at the location of the second party 130 . this information may consist of a simple alert such as a tone signal or flashing light - emitting diode ( led ) indicating the possible presence of a third party . the alert may include a numeric indicator of the likelihood that a third party is present . for example , a value of 0 . 0 may be used to indicate that a third party is definitely not present , 0 . 5 to indicate that a third party is equally likely to be present or not , 1 . 0 to indicate that a third party is definitely present , and values such as 0 . 25 and 0 . 75 to indicate intermediate levels of confidence that a third party is present . this numeric indicator might be delivered to a monitoring system operated by the first party 110 , such as a computer system running monitoring software , or it might be displayed directly to the first party 110 , perhaps depicted by a graphical indicator such as a bar graph , similar to the bar graph shown on cellular phones indicating signal strength . the alert may optionally contain descriptive information about the apparent third parties , such as whether the outside party appears to belong to a class of people from whom the communication 100 should remain private , or a numeric indication of the likelihood that a third party 140 is a potential eavesdropper . the system 200 comprises a mobile communication device 210 with sensors 240 , an analytical mechanism 220 , and a notification system 230 . the mobile communication device 210 is carried and used by the second party 130 . optionally , both parties may carry the mobile communication device 210 . possible forms of the mobile communication device 210 include , but are not limited to , a pager , a notebook computer , a cellular phone , a personal digital assistant , and a converged device that performs multiple functions , such as those of a cellular phone , personal digital assistant , and digital camera . the analytical mechanism 220 interprets data from the sensors 240 and deduces the likely proximity of potential eavesdroppers ( outside parties ). the analytical mechanism 220 may comprise any information processing hardware ( including but not limited to computing devices ), software , or a combination of hardware and software . it may be located entirely on the mobile communication device 210 , it may be distributed over the mobile communication device 210 and one or more other platforms , or it may be distributed over one or more platforms that do not include the mobile communication device 210 . these other platforms may be computing devices connected through a computer network such as the internet . the analytical mechanism 220 compares sensor data with profiles of sensor data expected when one or more outside parties is in proximity . the analytical mechanism 220 may be a computer processor executing analytical software in which the analytical mechanism 220 interprets combinations of data from multiple sensors . moreover , one or more functions of the analytical mechanism 220 can be performed in one or more of the sensors 240 . the notification system 230 is responsible for informing the first party 110 of the likely presence of potential eavesdroppers in the vicinity of the second party 130 examples of the sensors 240 comprise radio - frequency receivers , microwave sensors , infrared sensors , cameras , ultrasound sensors , microphones , and human - input devices . in an application — such as one restricted to a secured building , all of whose occupants are required to wear an identification badge — the radio - frequency receiver may be an rfid - tag ( radio - frequency identification - tag ) reader for an rfid tag embedded in the badge , or an active - badge reader for a radio - frequency transmitter embedded in the badge . similarly , a radio - frequency receiver could be used to detect the presence ( but not necessarily the content ) of transmissions to or from other portable communication devices in the proximity . these transmissions can include , for example , ieee 802 . 11a , 802 . 11b , 802 , 11g , and 802 . 11n wireless local area network transmissions ; bluetooth or zigbee transmissions ; or cellular phone transmissions . an example of a microwave sensor is a radar sensor . either a radar sensor , an infrared sensor , or an ultrasound sensor may be capable of detecting the presence , distance , or motion of a person or other object , or some combination of these properties . in addition , a radar sensor , an infrared sensor , or an ultrasound sensor may be capable of detecting the contours of a person or other object , while a camera would be capable of detecting its appearance from a particular perspective . various sensors 240 may be most effective when situated in a particular way , for example above the heads of people in a crowd , or at some distance from the second party 130 or the mobile communication device 210 of the second party 130 . therefore , the present invention anticipates that one or more of the sensors 240 may be detached or detachable from the communication device 210 . in a preferred embodiment , detached sensors would communicate with the mobile communication device 210 wirelessly , for example using bluetooth or zigbee . detached or detachable sensors may be accompanied by adhesive tape , hooks , telescoping poles , or telescoping tripods to facilitate their effective placement . of course second parties 130 may themselves become aware of nearby third parties 140 , either on their own or after being alerted by the system 200 to suspicious sensor readings . therefore , the sensors 240 may also include a conventional human - input device through which second parties 130 could directly communicate their awareness of nearby third parties 140 . examples of such devices comprise buttons , keyboards , microphones for sensing a second party &# 39 ; s spoken input , and cameras for sensing a second party &# 39 ; s gestures or lip movements . the input provided by the second party 130 may include supplementary information about the third parties 140 . examples of such supplementary information comprise whether or not a particular outside party is known to the second party 130 ( and if so , the identity of that outside party ), the apparent organizational affiliations of the outside party , the distance of the outside party from the second party 130 , the current activities of the outside party , and whether the outside party appears to be paying attention to the second party &# 39 ; s communications . the first party &# 39 ; s request for information may specify the particular types of supplementary information that the first party 110 desires . the system supports a protocol in which a first party 110 , desiring to communicate sensitive information , asks one or more second parties 120 to observe and evaluate their current levels of privacy , and to use their human - input devices to provide information of the kind just described . the supplementary information may include the level of threat posed by one or more outside parties to privacy of communication , based on such attributes such as , but not limited to , whether an outside party is known to the second party , the organizational affiliations of an outside party , the proximity of an outside party , the current activities of an outside party , and whether an outside party appears to be paying attention to the communication between the first party and the second party 120 . in one variation , depicted in fig3 , the system may require this exchange to take place at the beginning of a communication , before any substantive information is exchanged : the first party 310 sends the second party 320 a request 330 for information about how private the communication is likely to be , and the second party 320 responds with this information 340 , after which the first party 310 is permitted to send sensitive or non - sensitive information 350 to the second party 320 . in another variation , depicted in fig4 , this exchange may take place in the middle of a communication in which non - sensitive substantive information 430 has already been exchanged : at some point , desiring to transmit sensitive information , the first party 410 sends the second party 420 a request 440 for information about how private the communication is likely to be , and the second party 420 responds with this information 450 , after which the first party 410 is permitted to send sensitive information 460 to the second party 420 . in either case , the system may automate or facilitate the first party &# 39 ; s request for information from the second party , the second party &# 39 ; s response , or both . the analytical mechanism 220 uses raw data from the sensors 240 to deduce the likely presence and nature of third parties . the analytical mechanism 220 may interpret combinations of data from multiple sources , for example to reach more reliable conclusions about the likely presence of an outside party or to reach more reliable conclusions about the degree of threat to privacy of communications posed by a particular outside party . the analytical mechanism 220 may compare sensor data with profiles of data expected when an outside party is present . the analytical mechanism 220 may include low - level components within the sensors 240 themselves , medium - level mechanisms within the mobile communication device 210 , high - level mechanisms elsewhere within the overall presence - information system 200 ( perhaps on a computing device accessed over a network ), or some combination of these . the analytical mechanism 220 compares sensor data with profiles of sensor data expected when one or more outside parties is present a low - level component may detect motion from raw infrared readings or distances from raw radar returns , for example . a medium - level component may identify objects within images , or distinguish radio - frequency transmissions emanating from the second party &# 39 ; s own mobile communication device 210 and from local wireless - network infrastructure from transmissions emanating from outside parties , for example . a high - level component may perform database lookups , voice recognition , or face recognition , for example . of course other distributions of analytical functions over the components of the analytical mechanism 220 are also possible . examples of a notification system 230 include text messages , instant messages , e - mail , telephonic communications ( perhaps using synthesized speech ), graphical user interfaces , or a unified messaging system that delivers notifications to the first party in a manner that depends on the current milieu and activities of the first party . referring to fig5 , there is shown a simplified block diagram of the analytical mechanism 220 configured to operate according to one embodiment of the present invention . as shown , the analytical mechanism 220 may be an information handling system consistent with an embodiment of the present invention . for purposes of this invention , computer system 220 may represent any type of computer , information processing system or other programmable electronic device , including a client computer , a server computer , a portable computer , an embedded controller , a personal digital assistant , and so on . the computer system 220 may be a stand - alone device or networked into a larger system . the system 220 could include a number of operators and peripheral devices as shown , including a processor 506 , a memory 502 , and an input / output ( i / o ) subsystem 508 . the processor 506 may be a general or special purpose microprocessor operating under control of computer program instructions executed from a memory . the processor may include a number of special purpose sub - processors , each sub - processor for executing particular portions of the computer program instructions . each sub - processor may be a separate circuit able to operate substantially in parallel with the other sub - processors . some or all of the sub - processors may be implemented as computer program processes ( software ) tangibly stored in a memory that perform their respective functions when executed . these may share an instruction processor , such as a general purpose integrated circuit microprocessor , or each sub - processor may have its own processor for executing instructions . alternatively , some or all of the sub - processors may be implemented in an asic . ram may be embodied in one or more memory chips . the memory may be partitioned or otherwise mapped to reflect the boundaries of the various memory subcomponents . the memory 502 represents either a random - access memory or mass storage . it can be volatile or non - volatile . the system 220 can also comprise a magnetic media mass storage device such as a hard disk drive . the i / o subsystem 508 may comprise various end user interfaces 510 such as a display , a keyboard , and a mouse . the i / o subsystem 508 may further comprise a connection to a network such as a local - area network ( lan ) or wide - area network ( wan ) such as the internet . processor and memory components are physically interconnected using conventional bus architecture . the system 220 may also include at least one sensor for detecting proximity of an outside party . according to another embodiment of the invention , a computer readable medium , such as a cdrom 501 can include program instructions for operating the programmable computer 220 according to the invention . what has been shown and discussed is a highly - simplified depiction of a programmable computer apparatus . those skilled in the art will appreciate that other low - level components and connections are required in any practical application of a computer apparatus the presence detection method as described above may be further optimized for providing it as a fee - based service for users . a user of the service may subscribe monthly or pay for the service on a per - use basis . the service may be an add - on , purchased at the time a user purchases a mobile communication device . what has been shown and discussed is a highly - simplified depiction of a dynamic presence detection system , according to an embodiment of the present invention . those skilled in the art will appreciate that a variety of alternatives are possible for the individual elements , and their arrangement , described above , while still falling within the scope of the invention . the above descriptions of embodiments are not intended to be exhaustive or limiting in scope . the embodiments , as described , were chosen in order to explain the principles of the invention , show its practical application , and enable those with ordinary skill in the art to understand how to make and use the invention . it should be understood that the invention is not limited to the embodiments described above , but rather should be interpreted within the full meaning and scope of the appended claims .