Patent Publication Number: US-6342834-B1

Title: Personal security system with alarm location tracking

Description:
DESCRIPTION 
     Field of Invention 
     The invention relates to a personal security system for locating emergency transmissions. More specifically the invention pertains to such systems including a portable communicator actuated in an emergency to send wireless signals that are used by a monitoring station to locate and display the location of the sending communicator. 
     BACKGROUND OF THE INVENTION 
     Recently developed personal security systems locate subscribers in an emergency. The systems are installed in a protected region, such as a college or hospital campus, shopping center or building complex, and display the location of the emergency on a monitor at a central station. 
     A typical system is based on a portable transmitter carried by a subscriber and actuated in an emergency to send radio frequency signals identifying the transmitter to the system. Fixed receivers are installed at predetermined locations throughout the protected region. The receivers detect emergency transmissions and relay the transmitted information to the central monitoring station. The monitoring station identifies the subscriber to which the transmitter is assigned, locates the emergency based on the receivers that detect the transmission and displays the location to call appropriate security personnel. Examples of these and similar systems are disclosed in Shields U.S. Pat. No. 4,998,095, issued Mar. 5, 1991; DeMarco U.S. Pat. No. 4,764,757, issued Aug. 16, 1988; Levinson U.S. Pat. No. 4,611,198, issued Sep. 9, 1986 and Toner U.S. Pat. No. 5,365,217, issued Nov. 15, 1994. 
     Improved approaches for locating an emergency transmission are disclosed in Kostusiak et al. U.S. Pat. No. 5,115,224, issued May 19, 1992, and Malvaso et al. U.S. Pat. No. 5,416,466, issued May 16, 1995. In addition to the known positions of the detecting receivers, Kostusiak and Malvaso use relative signal strength between several receivers to more accurately locate the emergency transmission. 
     While existing approaches provide many advantages in personal security systems, they generally identify or display only a single location for each emergency. If a subscriber flees from an attacker, or is forced under duress to accompany the attacker, the system does not track the movement or display the path or direction of travel. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to improvements in personal security systems and overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the invention, a portable communicator, for use with a personal security system, includes a transmitter for sending wireless signals identifying the communicator to the system. A manually operated actuator initiates the transmission, which is then repeated automatically over a predetermined time interval exceeding five minutes. The transmissions are discontinued at the end of the predetermined time interval or by operating the communicator in a second non-emergency mode such as a test. According to more specific features, the transmissions repeat at least once a minute for a predetermined time interval exceeding ten minutes. Still more specifically, the identifying signals are transmitted as a multi-packet signal stream repeated approximately once every thirty seconds for an interval of approximately fifteen minutes. The transmitter is dormant between transmissions. 
     According to other aspects of the invention, the identifying signals include a tracking bit that is set to a first state for the manually initiated transmission and a second state different from the first state for the automatic transmissions. The tracking bit permits differentiation at a monitoring station between the manually initiated and automatic transmissions. 
     Other aspects of the invention include a plurality of fixed receivers at predetermined locations in a protected region for detecting the emergency transmissions and a central monitoring station that locates the transmissions based on the fixed receivers detecting the transmissions. The monitoring station tracks and simultaneously displays multiple locations of successive transmissions. More specifically, the monitoring station compares the locations of first and second successive transmissions, a) displays both locations when they are spaced more than a predetermined distance, and b) displays only the first of the two locations when they are spaced less than the predetermined distance. The monitor represents the multiple locations as icons that vary in size based on relative transmission time and are stacked so that any overlapping icons representing more recent transmissions are on top. 
     These and other features and advantages of the invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 and 2 are schematic views of a personal security system in accordance with a preferred embodiment of the invention including fixed receivers, local control centers and a monitoring station in FIG. 1 and a portable communicator in FIG.  2 . 
     FIG. 3 is a schematic diagram of the portable communicator of the preferred embodiment. 
     FIG. 4 is a schematic diagram of a signal packet transmitted by the communicator according to the preferred embodiment. 
     FIG. 5 is a flow diagram summarizing the operation of the preferred communicator. 
     FIG. 6 is a flow diagram depicting further details of the communicator operation according to the preferred embodiment. 
     FIG. 7 is a flow diagram depicting the operation of the fixed receivers and relays according to the preferred embodiment. 
     FIGS. 8 and 9 are flow diagrams depicting the operation of the monitoring station according to the preferred embodiment 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIGS. 1 and 2, a preferred embodiment of the invention is depicted in a personal security system including hand-portable communicators  10 , fixed receivers  12 , local control centers  14 , alarms  16  and a central monitoring station  18 . 
     The communicators  10  are carried by subscribers to the system for actuation in emergency or threatening situations to initiate planned events that scare away attackers and call for assistance. When actuated, the communicator transmits wireless signals to the surrounding area, at a predetermined frequency and signal strength, including a code that identifies the communicator to the system. 
     Receivers  12  monitor the protected region for transmissions and, in combination with local control centers  14  and central monitoring station  18 , initiate the planned events. The receivers detect and decode information from each transmission, including the identification of the transmitting communicator and the strength of the received signal. The identification and strength information is stored in the receiver for retrieval by the local control centers  14 , which repeat or forward the retrieved information to monitoring station  18 . The monitoring station uses the forwarded information to determine the location of the transmitting communicator and the name of the subscriber to which the communicator is assigned. Alarms  16  are actuated in the vicinity of the determined location, and security personnel are dispatched to that location for assistance. 
     Once actuated to transmit an emergency signal, the communicator  10  repeats the transmissions, preferably once every thirty seconds, for a predetermined time interval, preferably fifteen minutes. The central monitoring station  18  uses the signal repetitions to track and display any movement of the transmitter associated, for example, with fleet from an attacker. 
     Communicators and Transmitted Signal 
     The hand-portable communicator  10 , most clearly shown in FIGS. 2 and 3, is battery powered and adapted for convenient carrying in a purse or pocket. It is enclosed in a plastic case  20  including a key ring  22  and two switches depicted as depressable buttons  24  and  26 . The switches are designed for actuation from opposite sides of the case  20  against a spring bias and in sequences that normally prevent accidental operation. 
     The switches  24  and  26  initiate operation of the communicator, either in an alarm state or a test state, depending on the sequence of actuation. In both cases, alarm and test, the communicator produces and transmits a radio frequency signal to the local geographic area at a predetermined frequency and signal strength. The frequency may be in the three hundred or nine hundred megahertz range typical for such applications. The signal strength is chosen in combination with the number and locations of fixed receivers  12  so more than one and preferably at least three receivers typically will be able to detect the transmitted signal for the purposes to be described. At the same time, the signal strength, which falls off with the inverse square of the distance, should be weak enough to facilitate the location of the transmission based on differences in the signal strength at the detecting receivers. 
     Actuation of the switches  24  and  26 , in either an alarm or a test mode, causes a microcontroller  28  (FIG. 3) to initiate operation of a transmitter  30 , sending the radio frequency signals through antenna  32  to the local geographic area. The transmitted signal, sometimes referred to as a signal stream, includes a series of eight identical packets of information  34  (FIG. 4) having an irregular spacing in the stream to reduce the risk of jamming with other possible transmissions. The packets take approximately sixteen milliseconds to transmit, with approximately one hundred milliseconds between packets. A signal stream of eight packets takes approximately one second to transmit. Each packet contains the information identified on FIG. 4, including a preamble  36 , a user or transmitter identification (ID) code  38 , an alarm or test code  40 , a tracking bit  42 , a low-battery warning bit  44 , and a check sum  46  for error detection. Appropriate memory  48  and  50  (FIG. 3) are included in the communicator to support the microcontroller in carrying out its various functions. 
     The transmitter ID code  38  is programmed and stored in memory  48  or  50 , either at the time of manufacture or when the user subscribes to the system. The alarm or test code  40  is determined by the manner in which switches  24  and  26  are actuated. Simultaneous actuation of the switches  24  and  26  sets the code to indicate an alarm. Sequential actuation, first one switch and then the other, sets the code to indicate a test. The tracking bit  42  is set by the microcontroller  28 . For reasons that will become more apparent from the following description, on the first or manually initiated transmission of an alarm, the tracking bit  42  is cleared to indicate the first transmission. During subsequent automatic transmissions, however, the tracking bit is set. 
     FIG. 5 summarizes the operation of the portable communicator, which will be described in combination with FIGS. 1-4. Beginning at  52 , the switches  24  and  26  are actuated sequentially to initiate a test, boxes  54  and  56 , or simultaneously to initiate an alarm, boxes  58  and  60 . Microcontroller  28  operates transmitter  30  to send the signal packet  34  with the alarm/test code  40  set to appropriately indicate a test or an alarm in accordance with the mode of switch operation. For a test, the signal stream of eight packets is transmitted only once. For an alarm, on the other hand, the signal stream is transmitted repeatedly, such as more frequently than once a minute, for a predetermined time interval of at least five minutes, and preferably at least ten minutes. In this preferred embodiment the transmissions are repeated approximately every thirty seconds for approximately fifteen minutes. The alarm signal repetitions are depicted at  60 ,  62  and  64 . 
     The same operation is represented in more detail in FIG. 6, again with reference to FIGS. 1-4. Sequential actuation of switches  24  and  26  (FIGS. 2 &amp; 3) initiates a single transmission of the test signal, boxes  66  and  68 . Simultaneous operation, on the other hand, initiates repeated transmissions of the alarm signal, boxes  70 ,  72 ,  74 ,  76 ,  78 ,  80 , and  82 . Timers are set at  72 : 1) one for the next transmission or repetition interval, and 2) another for the overall alarm timeout. At  74 , the tracking bit is cleared and the first transmission occurs. At  76 , the repetition interval times out, and at  78  and  80  the signal transmission is repeated with the tracking bit set. This cycle repeats until the overall alarm times out, box  82 , and the transmissions automatically are discontinued. 
     The repeated alarm transmissions can be discontinued manually at any time by initiating a test transmission, boxes  84  and  86 , which cancels the alarm, box  88 . 
     If another manual alarm is initiated by simultaneous actuation of switches  24  and  26  during the automatic cycle, the manual alarm overrides and restarts the automatic sequence as indicated at  90 . 
     Receivers, Alarms and Local Control Centers 
     The receivers  12  (FIG. 1) include a plurality of receivers, exemplified by  92 ,  94  and  96 , spaced at predetermined locations throughout the protected area. Each respective receiver is tuned to continuously monitor the predetermined frequency used by the portable transmitters. They decode transmitter signals, validate the transmission for proper format, sample the strength of validated signals and set a normal/off-normal bit flag depending on the information received. A decoded transmission, assuming it is in the proper format, is stored in a data register, including the received signal strength, the identification number of the portable transmitter and the state of the normal/off-normal flag bit. 
     The receivers communicate with their associated local control center  14  through a multiplex bus interface  98 . The local control center  14  queries each respective receiver using a unique receiver address code. If the flag bit is normal, the control center  14  continues with queries cycled to other receivers. If the flag bit is off-normal, indicating, for example, either an alarm or a test, the local control center  14  requests the stored information. This includes the reason for the off-normal condition, e.g. alarm or test, the strength of the received signal and the identification code of the sending transmitter. The local control center  14  also links the retrieved transmitter and signal information with an identification code associated with the receiver that is holding the information. 
     Several receivers, such as  92 ,  94  and  96 , preferably will receive, store and transfer information connected with a single alarm or test. The local control center  14  sends the information, including received signal strength, transmitter identification, and receiver identification, on to the central monitoring station  18 . The central monitoring station uses the information, and any other information that might be received from other local control centers, to display on a monitor  100  icons representing the location of the detecting receivers. The central monitoring station also uses the information to calculate and display an icon representing the predicted location of the transmitting communicator. 
     If the off-normal condition is caused by an alarm, the local control center  14  and central monitoring station  18  will issue commands activating a sounder  102  and strobe  104  closest to the above-mentioned receivers. A horn  105  associated with each detecting receiver also is energized. If the off-normal condition is caused by a test, the central monitoring station  18  will use the unique identification of the portable transmitter to look in its records for an active subscriber, and will indicate the results of the test by energizing a green or red light emitting diode (LED)  106  or  108 , respectively, on the detecting receivers. The red LED might be actuated, for example, to indicate an expired subscription, while the green LED would indicate a successful subscriber test. 
     The operation of the local control center is summarized as a flow diagram on FIG.  7 . The receivers are scanned at  110 . If the off-normal flag indicates that an alarm or test transmission was detected,  112 , the information stored in the detecting receiver(s) is retrieved at  114 , and the information in the strongest signals is forwarded to the central monitoring station at  116 . The forwarded information includes the identification of the transmitting communicator, the identification of the detecting receiver and the received signal strength at the detecting receiver. The local control center then receives acknowledgments from the central monitoring station  18  and implements commands from the station at  118 . 
     Central Monitoring Station 
     Central monitoring station  18  (FIG. 1) includes a transceiver  120  and computer  122  with monitor  100 . The central monitoring station communicates with the local control centers  14  for controlling the sounders and strobes  102  and  104  in the alarm mode and the red and green LEDs  106  and  108  in the test mode. The central monitoring station also is used for entering system information and parameters. It might include a map of the protected area and a program for showing the locations of receivers in the vicinity of an alarm or test transmission. Typically, the central monitoring station will store subscriber records including active or inactive status, identification of the portable communicator assigned to each subscriber, and the times and locations from which it was used, either in an emergency or for a test. 
     The central monitoring station also locates and tracks any movement of a transmitting communicator as depicted by the flow diagram of FIGS. 8 and 9. 
     Beginning with FIG. 8, the central monitoring station acknowledges tests and issues commands to energize the appropriate LED  106  or  108 , boxes  124  and  126 . When an alarm is received, box  128 , the station looks in memory to determine if the alarm is the first alarm received for this event, box  130 . If it is not the first alarm, the flow diagram proceeds as depicted in FIG. 9, described hereinafter, box  132 . If it is the first alarm, the monitoring station uses the tracking bit to determine if the alarm is a manual alarm, box  134 , or an automatic alarm, box  136 . A manually initiated alarm is identified by a cleared tracking bit  42  (FIG.  4 ), while an automatic transmission is identified by a set tracking bit. 
     A manual alarm is recorded in memory at  138  and the transmitted information is used to compute and display the location of the transmitting communicator, boxes  140  and  142 . The alarm is sounded, box  144 , and an event timer is started, box  146 . The event timer times out in ten seconds, and is used to determine if the detected transmissions are from a single communicator transmission or multiple communicator transmissions. A single transmission might be detected at several receivers, and this is the assumption made by the central monitoring station whenever they are received and reported within the ten seconds event timeout. 
     Even though an alarm is recognized and cleared centrally, the communicator will continue to transmit for fifteen minutes or until a test transmission is initiated. In this case, the central monitoring station may receive a first alarm that is not a manual alarm but corresponds to an alarm recorded in memory within the past fifteen minutes. As represented by box  136 , the monitoring station assumes that appropriate action has been taken and no further alarm is required. 
     Referring now to FIG. 9, if the ten second event delay has not expired, box  148 , the alarm information is assumed to be from a single transmission. The alarm information is then used with other data from the same transmission to determine and display the location of the transmitting communicator, boxes  150 ,  152  and  154 . The monitoring station also determines if the transmitting communicator has moved and compares the most recently determined location to any prior location. If the transmitting communicator moved a distance greater than a predetermined amount, preferably thirty feet, or half the diameter of its corresponding monitor icon, the most recent location and the prior two locations are simultaneously displayed on the monitor. If the location has not changed by the predetermined amount, no change in location is displayed. 
     The prior locations are displayed first, and are represented by smaller icons. The icon representing the oldest location is displayed first, followed by the icon representing the next most recent location, which is in front of and twice the diameter of the first icon, followed by the icon representing the most recent location, which is in front of and twice the size of the previously displayed icon. All three locations are displayed simultaneously to show the direction and path of travel. The respective locations also may be displayed in different colors compared to other locations. 
     If the ten second event delay has expired, box  148 , the central monitoring station assumes that the alarm is from another transmission, probably an automatic transmission. The transmitted information is used to determine a new alarm position, and the stack of alarm positions is shifted with the most recent position being added to the stack, box  156 . 
     A new manual alarm, box  160 , restarts the alarm if it has been silenced, boxes  162  and  164 , and restarts the alarm sequence, box  166 . 
     It should now be apparent that the invention provides an improved personal security system that locates emergency transmissions and indicates the direction or path of any movement after the first transmission. Multiple successive locations are displayed simultaneously on a monitor. The monitor presents the multiple locations as icons that vary in size based on relative transmission time and are stacked so that any overlapping icons representing more recent transmissions are on top. 
     While the invention is described in connection with a preferred embodiment, other modifications and applications will occur to those skilled in the art. The claims should be interpreted to fairly cover all such modifications and applications within the true spirit and scope of the invention. 
     PARTS LIST 
     Reference No. Part 
       10 . Communicator. 
       12 . Receivers. 
       14 . Local control center. 
       16 . Alarms. 
       18 . Central monitoring station. 
       20 . Case. 
       22 . Key ring. 
       24 . Button. 
       26 . Button. 
       28 . Microcontroller. 
       30 . transmitter. 
       32 . Antenna. 
       34 . Information packet. 
       36 . Signal preamble. 
       38 . Identification code. 
       40 . Alarm or test code. 
       42 . Tracking bit. 
       44 . Low-battery warning bit. 
       46 . Check sum. 
       48 . Memory. 
       50 . Memory. 
       52 - 90  (even numbers). Flow diagram. 
       92 . Receiver. 
       94 . Receiver. 
       96 . Receiver. 
       98 . Bus Interface. 
       100 . Screen. 
       102 . Sounder. 
       104 . Strobe. 
       105 . Horn. 
       106 . LED. 
       108 . LED. 
       110 - 118  (even numbers) Flow diagram. 
       120 . Transceiver. 
       122 . Computer. 
       124 - 166  (even numbers) Flow diagrams.