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Claims  |
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What is claimed is:
1. A tag for use with an individual monitoring system comprising:
a self-contained power source;
circuit means coupled to said power source for periodically generating an
encoded signal, said encoded signal including identification information
and status information;
sensing means for sensing when said tag is held near human flesh; and
mode control means for allowing said circuit means to selectively operate
in one of a plurality of operating modes;
said status information including an indication of whether said tag is
being held near human flesh; and
said mode control means including switch means responsive to the
application of an external force, and wherein said operating modes
include:
an off mode, wherein no external force has yet been applied, and the
circuit means of said tag is disabled, thereby conserving the energy of
said self-contained power source,
a start-up/test mode, initiated by applying and maintaining said external
force, during which said circuit means is enabled and operates in a test
mode that allows operation of the tag to be verified, and
a normal run mode, initiated upon removal of the external force, during
which said circuit means generates said encoded signal at prescribed
intervals.
2. The tag of claim 1 wherein said operating modes further include:
a CW mode, initiated by reapplying and maintaining said external force,
during which said encoded signal is not generated, but during which a
noncoded continuous RF signal is generated.
3. The tag of claim 1 wherein said external force comprises a magnetic
force.
4. The tag of claim 1 wherein said sensing means for sensing when said tag
is held near human flesh comprises means for sensing a change in the
capacitance between spaced-apart electrodes or conductors mounted in said
tag, said electrodes being placed near the skin of a person who is to
carry said tag, the flesh of the person thereby comprising a portion of
the dielectric material between said spaced-apart electrodes, the absence
of said dielectric material, as occurs when the tag is removed from the
skin of the person, thereby affecting the capacitance that exists between
said spaced-apart electrodes.
5. The tag of claim 4 wherein one of said spaced-apart electrodes comprises
a plate mounted in a surface of said tag and the other of said electrodes
comprises a conductive element in a strap used to hold said tag near the
flesh of the individual.
6. The tag of claim 5 wherein said strap, including the conductive element
therein, is realized from conductive material.
7. The tag of claim 1 wherein said sensing means for sensing when said tag
is held against human flesh includes a strap connected to said tag, which
strap wraps around a limb, such as a leg or an arm, of the person carrying
the tag, and wherein strap-breaking detection means are provided to detect
if said strap is broken, opened, or otherwise removed from said tag.
8. The tag of claim 1 wherein said circuit means comprises
a low power oscillator for generating a repetitive clock pulse;
counting circuitry responsive to said clock pulse for generating timing
signals;
encoding circuitry responsive to said timing signals for generating said
encoded signal based on a preset identification code and said sensing
means; and
RF transmitting means for generating and transmitting an RF signal
modulated by said encoded signal at prescribed intervals as controlled by
said timing signals.
9. The tag of claim 8 wherein said RF transmitting means includes a crystal
controlled oscillator for controlling the frequency of said RF
transmitting means, whereby the RF signal generated has a stable frequency
associated therewith.
10. A tag for use in a system for monitoring the presence of an individual
within a defined area, said system including attachment means for
attaching the tag to the individual, receiving means positioned within
said defined area for receiving identification signals generated by said
tag, and processing means coupled to said receiving means for noting the
time of receipt of the received identification signals, from which time
information a determination can be made as to the presence or absence of
the individual within the defined area during any given time period, said
tag comprising:
a first power source,
sensing means for sensing a plurality of prescribed tamper conditions
associated with the operation and use of said tag, said sensing means
comprising:
means for holding the tag near the skin or flesh of the individual, said
holding means comprising a conductive strap attached to said tag that fits
around a limb of said individual and holds the tag against said limb,
first circuit means for sensing the presence or absence of said skin or
flesh near said tag, and
second sensing means for sensing the continuity of said conductive strap,
whereby the cutting or breaking of said strap can be sensed; and
means coupled to said first power source for transmitting an identification
signal, said identification signal including identification information
that uniquely identifies said tag, and hence the individual to whom the
tag is attached, and status information that indicates the prescribed
conditions sensed by said sensing means.
11. A tag for use with a monitoring system, said tag including carrying
means for allowing said tag to be carried by a movable object, said object
having a surface against which said tag is carried, and transmitting means
for transmitting an identifying signal to said monitoring system over a
prescribed transmission range, said monitoring system including means for
receiving said identifying signal, whereby the receipt of said identifying
signal provides an indication to the monitoring system that the tag is
physically located within the prescribed transmitting range from said
monitoring system, said tag including:
first circuit means for sensing any attempt to remove said tag from said
object;
second circuit means for sensing whether said tag is being held near the
surface of said object; and
means coupled to said first and second circuit means for modifying the
identification signal to include status information indicating the
condition of said tag relative to the sensing functions carried out by
said first and second circuit means;
whereby the monitoring system can determine through receipt of said
modified identification signal whether an attempt to remove said tag from
said movable body has been made and whether said tag has been removed from
said movable body.
12. The tag of claim 11 wherein said movable object comprises an ambulatory
object having skin, and wherein said second circuit means senses whether
said tag is within a prescribed distance of said skin.
13. The tag of claim 11 wherein said carrying means comprises a strap
adapted to fit around a part of said object; and further wherein said
first circuit means senses the continuity of said strap, whereby any
breaking or opening of said strap can be detected.
14. The tag of claim 13 wherein said strap includes a conductive material
that allows an electrical signal to pass therethrough, whereby the
continuity of the strap can be measured to determine whether the strap has
been broken, said electrical signal being provided by said first circuit
means.
15. A tag for use with a monitoring system, said tag including carrying
means for allowing said tag to be carried by an ambulatory movable object,
said ambulatory movable object having skin or flesh near which said tag is
carried, said tag further having transmitting means for transmitting an
identifying signal to said monitoring system over a prescribed
transmission range, said monitoring system including means for receiving
said identifying signal, whereby the receipt of said identifying signal
provides an indication to the monitoring system that the tag is physically
located within the prescribed transmitting range from said monitoring
system, said tag including:
circuit means for sensing the presence or absence of said skin or flesh
near said tag; and
means coupled to said circuit means for modifying the identification signal
to include status information indicating the condition of said tag
relative to the sensing function of said circuit means;
whereby the monitoring system can determine through receipt of said
modified identification signal whether said tag has been removed from said
movable body.
16. The tag of claim 15 wherein said movable object comprises an ambulatory
object having skin, and wherein said circuit means senses whether said tag
is within a prescribed distance of said skin. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
The present invention relates to a tag for use with a personnel monitoring
system. More particularly, the invention relates to a tag for use with a
house arrest or other monitoring system wherein individuals who wear the
tag can be monitored for compliance with orders or instructions to remain
at a prescribed location. Even more particularly, the present invention
relates to such a tag that includes anti-tamper circuits therein so that
any attempt to remove the tag can be detected and signaled to a central
monitoring location.
To illustrate a potential application of a personnel monitoring system,
reference is made to a newspaper article appearing in the Los Angeles
Times on Wednesday, Sep. 12, 1985, Part I, page 3. The article indicated
that on Tuesday, Sep. 10, 1985, U.S. District Judge Terry J. Hatter, Jr.
sentenced David Alan Wayte to spend "six months under house arrest at his
grandmother's home for failing to register for the military draft." While
this was reported as "one of the most unusual sentences in recent memory,"
it is believed to represent a major trend for future sentencing of
non-violent offenders. This is particularly evident in view of the ever
overcrowded prisons and jails that exist in every jurisdiction across the
U.S. and throughout the world. House arrest thus represents a very
significant and viable alternative to conventional incarceration of
convicted law breakers, especially those found guilty of non-violent
crimes.
While those sentenced to house arrest will generally recognize the need and
benefit of complying with the sentence imposed, there nonetheless remains
the need to monitor the presence or absence of such individuals to ensure
that the sentence imposed is being followed so that justice can be
satisfied. For example, in the instance cited above, the attorneys for the
convicted individual, David Wayte, wanted the judge to impose community
service work as punishment. While community service may be a very
appropriate sentence to impose in some instances, the judge felt that
because Mr. Wayte was already doing community service on a regular basis,
a sentence of house arrest should be imposed to punish Wayte by not
allowing him to perform such service. Hence, if Wayte were to violate his
sentence by leaving his grandmother's house without the knowledge of the
court, the purposes of Judge Hatter's sentence would be frustrated.
While monitoring the presence or absence of a single individual at a
prescribed location may seem like an easy task, it really is not.
Moreover, where there are a large number of individuals who must be
monitored, each at a different "house-arrest" location, the problem
becomes exceedingly more complex, especially where some of the individuals
may not want to fully comply with the need to wear the tag at all times.
Hence, there is a need in the art for a system that can efficiently and
accurately monitor the presence or absence of a large number of
individuals who have been sentenced to remain at specific locations under
house arrest. Advantageously, such a system could also be used to monitor
the presence or absence of those individuals on parole, i.e., those
individuals who are more or less free to move about as they want during
certain hours of the day, but who must "report in" at specified locations
at specified times. There is a further need to provide a tag that can be
comfortably worn by those individuals being monitored but that can not be
removed or tampered with without being detected.
The present invention meets this need by providing an electronic monitoring
system that inexpensively and accurately monitors the house-arrest
location of a large number of individuals at a wide variety of different
locations. Moreover, such monitoring is accomplished in a way that is not
readily noticeable to those persons with whom the monitored individuals
come in contact at the house-arrest location, and in a way that is
essentially tamper-proof and secure, with suitable alarm messages being
promptly given at a central monitoring location in the event that anything
out of the ordinary is sensed at a given house-arrest location.
Electronic monitoring systems used to determine and monitor the location of
individuals are known in the art. The concept of such electronic personnel
monitoring systems probably existed long before the technology was
available to realize them. Fictional accounts have long referred to the
concept of an electronic personnel monitoring system (e.g., the "Spider
Man" comic strip). Numerous press reports have also broadly discribed the
benefits of such systems, but have not disclosed the technology for how
such systems could be realized, other than in the broadest of terms.
In Schwitzgebel, et. al., U.S. Pat. No. 3,478,344, there is disclosed a
prisoner monitoring system that keeps track of the location of prisoners
within a specified boundary. This is accomplished by a system that uses RF
transmitters, mounted on the wrist of the prisoner being monitored, and an
array of directional antennas that can determine the location of a
transmitter with respect to the antenna array. The wrist RF transmitter is
powered by a battery pack worn on the prisoner's belt. Two batteries are
employed so that the unit remains powered if one battery is removed. The
wrist band includes a conductive wire therein that, if broken or cut, is
used to signal that the wrist band has been improperly removed.
While the system disclosed in Schwitzgebel may have represented an
important advance in the art at the time it was made (1965), there are
many reasons why the system disclosed in Schwitzgebel may not provide a
viable house arrest system for use today. For example, the large battery
pack is unsightly and is cumbersome for the prisoner to wear. The antenna
array that must be placed around the premises is likewise unsightly and
draws attention to the fact that the location is being monitored.
Moreover, the conductive wire check of the wrist band could be easily
circumvented if a prisoner wanted to remove the device without being
detected. Further, external RF signals could easily interfere with the
intended RF signal, or external RF signals could be beamed into the
monitored area by an outside accomplice in order to "jam" the system.
In Mandel, U.S. Pat. No. 3,898,984, an ambulatory patient monitoring system
is disclosed. A telemetry system using a single RF frequency for each
individual to which the system is attached monitors critical body
functions. FM modulation is used. A transponder unit worn by the
individual is triggered by an interrogating signal, in response to which
interrogating signal selected information about the individual, as sensed
by special sensors on the individual, is transmitted to a receiver. In
this way, the receiver is able to monitor certain body functions of the
patient being monitored. However, location information about the patient
is not included in the transmitted information.
In DePedro, U.S. Pat. No. 3,882,277, electrocardiograph information is
telemetered from a patient to a telephone transmission link system that
carries the information to a central monitoring location. Thus, a combined
telemetry and telephone transmission system is employed to monitor
physiological signals. However, as disclosed, such physiological signals
do not include the location of the patient being monitored.
In the UK Patent Application of Anders et. al., GB2141006A, a system is
disclosed that measures location, identification, or motion. The system
therein described uses "passive" tags that may be placed on movable
objects. The location of any of these movable objects may be ascertained
through a system that uses active transceivers to interrogate the passive
tags. In response to such interrogation, the passive tags transmit an
identification code. The location of the tag is sensed through the use of
multiple antennas spaced at predetermined intervals, or through
repeater-relay transceivers spaced at predetermined intervals, around the
area being monitored.
From the above it is seen that the prior art teaches electronic monitoring
systems that monitor the presence or absence of individuals from a
prescribed location and/or specified parameters of an individual at remote
locations. To accomplish such monitoring, it is known to use tags worn by
movable objects or individuals, RF telemetry to and from such tags,
repeaters, and telephone transmission links.
Despite these teachings of the art, however, no viable house arrest
monitoring system has yet been developed to applicant's knowledge. This is
because there are numerous features that must be present in a viable house
arrest monitoring system that are lacking in the teachings of the prior
art. For example, it is desirable to have the electronic tag or other
device that identifies the individual being monitored (usually some sort
of transponding device) to be worn at a location that is not readily
visible to the casual observer and at a location where it cannot be
removed by its wearer, but at a location where it will not unduly
interfere with the activities of its wearer. This requirement can be met
if the tag is worn on an ankle, thereby allowing the tag to be readily
concealed by the clothes (pants leg and/or sock) of its wearer. However,
such use causes the tag to be located very close to the ground, or floor
level. When the floor level comprises earth or concrete, as is often the
case, some significant transmission problems can result. This is because
the RF signal, by necessity a fairly weak signal that is generated for a
limited transmission range from a limited energy source, is either
absorbed in, or otherwise destructively reflected from the earth or
concrete surface. Further, concrete is often heavily laced with reinforced
steel, which also tends to interfere with reliable low-energy RF
transmissions. Moreover, the walls of the structure whereat the house
arrest is being performed may have wire mesh or other metal objects
therein that destructively interfere with the transmission of low-energy
RF signals.
Simply increasing the energy of the RF signals transmitted from the tag is
generally not a viable solution to this problem. In the first place, the
tag only has a limited energy source, and it is desirable to have this
energy source last for as long as possible. In fact, in accordance with
the teachings of the invention herein, the limited energy source (a
battery) should be permanently sealed in the tag so that the wearer of the
tag has no access thereto. In the second place, higher energy RF signals
create numerous other problems for those in the vicinity of the
transmission, and as such, must be carefully regulated by the FCC or other
regulatory agencies.
A further feature that desirably exists in a viable house arrest monitoring
system is that readily noticeable or visible antennas or antenna arrays
not be used. Such antennas immediately draw attention to the fact that a
house arrest situation exists. Accordingly, the antennas that are used
should be of the low profile variety that readily blend into the
surroundings of a typical house environment. Further, such antenna(s) and
related circuitry must be able to reliably pick up or sense the desired
signal and discriminate against destructive reflections or external
signals that may be present within the house-arrest structure.
Still a further feature that is of critical importance to the successful
use of a house arrest system is the integrity of the system. That is, all
components of the system at the house-arrest location must be able to
sense and signal the occurrence of any attempts to tamper therewith.
Further, while there is nothing that can absolutely prevent the
destruction of the system's components at the house arrest location, it is
desirable that such destruction or attempted destruction be promptly
communicated to a central processing location so that appropriate follow
up action can be performed. Most importantly, the electronic
identification (ID) tag that is worn by the person under house arrest must
not be removable. At a minimum, any attempts to remove the tag should be
detectable.
SUMMARY OF THE INVENTION
The present invention provides a realiable house arrest system that
automatically verifies the presence or absence of prisioners or other
personnel who are required to remain at a prescribed location or to report
in at the prescribed location at a certain time. Advantageously, the
prescribed location may be a conventional house, apartment, or other
building not intended for use as a prison or custodial facility.
Typically, the prescribed location will be a residential house or
apartment where other individuals, such as the family of the individual
being monitored, may live and work with the individual under house arrest.
While such other family members will typically not be under house arrest,
the present invention advantageously contemplates that more than one
individual under house arrest may share the prescribed house-arrest
location, each being individually monitored.
More specifically, the present invention is directed to an identification
tag that is worn by the individual under house arrest. Typically, this tag
will be worn on the ankle of the individual, and its small size
advantageously allows the clothing of the individual to readily conceal
the fact that the tag is being worn. The identification tag periodically,
such as every 120 seconds, transmits an identification signal that
includes a prisoner identification code. This code uniquely identifies the
individual being monitored. Other information is also included in the
transmitted signal, such as information indicating that someone has
attempted to tamper with or remove the tag.
The identification signal generated by the tag is received by a Field
Monitoring Device (FMD) that is located within the house-arrest location.
A repeater may be selectively positioned around or within the house-arrest
facility in order to assure that the FMD always receives an identification
signal regardless of the location of the tag (that is, regardless of the
location of the individual wearing the tag) within the facility or
surrounding environs. The repeater receives the information signal from
the tag, holds it for a very short time, and retransmits it. The reception
patterns associated with the FMD and the tag for all possible locations of
the tag within the facility are checked at the time of installation. This
initial check identifies any "dead spots" or tag locations where the tag's
identification signal is not properly received by the FMD. The repeater
can then be selectively positioned within the house-arrest facility in
order to eliminate the effect of such dead spots, thereby helping to
assure reliable communication between the tag and the FMD.
The FMD, in accordance with the preferred embodiment, includes a modem for
communicating with a central processing unit (CPU) via a telephone link.
Other types of communication links, such as microwave or satellite links,
could also be employed to couple the FMD to the CPU. Normally, the FMD's
will call the CPU whenever there is a change associated with the
identification signal sensed (received) by the FMD. For example, if the
identification signals have been regularly received from the tag and the
signal stops being received, the FMD will call the CPU and log a "leave"
message. If no signals are being received by the FMD and signals appear,
the FMD will call the CPU and log an "enter" message. Such time logs
permit the system to determine the approximate time when an individual
being monitored "checks out" or leaves and "checks in" or enters the house
arrest location. Additionally, the various FMD's call the CPU at
preestablished times stored by the FMD's and CPU's.
Advantageously, the FMD monitors the information signals received from each
tag (an FMD can receive signals from a plurality of tags) to determine if
a tamper condition exists. A tamper condition exists if any attempt is
made by anyone at the house-arrest location to monitor the presence and
absence and to remove, alter, or otherwise interfere with the normal
operation of the system, including the tag and the circuits of the FMD. In
such situations, the FMD includes the capability of calling up the CPU to
alert it of such a tamper condition.
The CPU is located at a remote location from the house-arrest facility, and
includes the means for establishing a telephone or other communication
link with a large number of FMD's at a large number of house-arrest
locations. As indicated above, the FMD's normally call the CPU whenever a
leave, enter or tamper condition occurs. Additionally, the CPU will call
the various FMD's on a random basis in order to determine if all is well
at each location called. If the CPU is unable to establish a telephone
link with a given FMD after a prescribed number of attempts, which failure
might occur, for example, if the telephone lines or other communication
channels had been tampered with, the CPU generates an alarm condition so
that appropriate steps can be taken to find out what has happened.
Similarly, if the CPU receives a call from an FMD indicating that a tamper
condition has been detected, an alarm condition is generated.
Advantageously, the CPU is programmed to generate a wide variety of
reports that can be used by the monitoring personnel in order to quickly
and efficiently determine the status of all of the individuals being
monitored at the various house-arrest locations.
A feature of the present invention is that the house arrest system, in
addition to automatically verifying the presence or absence of prisoners,
also monitors the operating condition of the equipment used, thereby
providing a means for allowing preventative maintenance to be performed in
a timely manner.
An additional feature of the present invention is that the identifying tag
worn by the prisoner or other individual being monitored is a
self-contained tag that is light-weight, tamper resistant, and that can be
worn on a limb of the individual in an unobtrusive manner. Further, the
tag is completely sealed, thereby protecting the electronic circuits
contained therein from exposure to damaging environments. The tag's
housing is made from a substance that is impervious to water and other
fluids to which the tag might be exposed. Further, the tag's housing is
made from a substance that is comfortable and safe to wear when placed
against the skin of the individual who must wear it.
Most significantly, an important feature of the present invention is that
once the tag is placed on the leg or other limb of the individual being
monitored, thereby placing the tag in proximity to the individual's skin,
any removal of the tag from the leg or other limb can be detected. This is
accomplished by combining a continuity check of a conductive strap or band
that holds the tag on the individual with a capacitive sensing circuit
that senses when the tag is near human flesh and when it is not.
Because the tag is sealed, including the battery that is used to power the
circuits contained therein, an important feature of the tag is the ability
to preserve the life of the battery for as long as possible. Accordingly,
the operating circuits of the tag are configured such that they can
initially be totally shut down, as when the tag is first manufactured but
before it has been assigned to be worn by an individual under house
arrest, thereby preserving the life of the batteries contained therein.
However, the tag circuits can be selectively switched to operate in a test
mode when the device is first used at a house-arrest location, thereby
allowing initial verification of the operation of both the tag and the
FMD, followed by a normal operating mode. Such modes of operation are
controlled, in the preferred embodiment, by the selective application of a
magnetic field.
A further feature of the present invention is that the system is able to
reliably operate even in very noisy RF environments. Special transmitting
circuitry housed in the tag, coupled with corresponding receiving
circuitry housed in the FMD, and additionally data decoding software allow
the FMD to reliably discriminate between the intended RF signal generated
by the tag and noise.
Still another feature of the present invention is the ability of the FMD to
continue its monitoring operation of the tag or tags within the prescribed
house-arrest location even in the event of a line power failure. Such a
power failure might occur, for example, if the FMD is unplugged (either
accidentally or on purpose), or if a wide-spread power failure hits the
area where the house-arrest facility is located. Further, even if
telephone service is temporarily interrupted, thereby precluding
communication between the FMD and the CPU, the FMD continues to store in
its memory the events that occur during this time, as sensed by the
various sensing circuits housed in the FMD and the information received
from the tag in its regularly transmitted information signal, for
subsequent replay back to the CPU once a communication link is
reestablished.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other features and advantages of the present invention will
be more apparent from the following more particular description thereof
presented in conjunction with the following drawings wherein:
FIG. 1 is a block diagram of the house arrest monitoring system of the
present invention;
FIG. 2 is a perspective view of the tag that is worn by an individual being
monitored by the system of FIG. 1;
FIG. 3A illustrates one manner in which the tag may be worn;
FIG. 3B shows a perspective view of the FMD;
FIG. 4 is a block diagram of the circuits contained in the tag of FIG. 1;
FIG. 5 is a schematic/logic diagram of the Tamper Detect and Strap
Continuity Check circuits of the Tag of FIG. 4;
FIG. 6 is a cross-sectional view of the tag as it is worn or placed near
the flesh or skin of its wearer, and illustrates the capacitive plates or
electrodes contained within the tag and strap and their relationship to
the flesh of the wearer;
FIG. 7 is a schematic/logic diagram of the Mode Control circuit of the Tag
of FIG. 4;
FIG. 8 is a chart or table that illustrates the operating modes of the tag
as controlled by the Mode Control circuit of FIG. 7;
FIG. 9 is a schematic/logic diagram of the ASMV and Encoding Logic of the
Tag of FIG. 4;
FIG. 10 is a timing diagram that illustrates some of the key signals
associated with the operation of the circuits of FIG. 9;
FIG. 11 is a schematic/logic diagram of the RF Modulator and Transmitter of
the Tag of FIG. 4; and
FIG. 12 is a block diagram of the FMD of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is best understood with reference to the drawings,
wherein like numerals are used to represent like parts throughout.
Referring first to FIG. 1, there is shown a block diagram of a house arrest
monitoring system 30 in accordance with the present invention. The system
30 includes a plurality of remote monitoring areas 32 and a central
processing unit (CPU) 34. The CPU 34 is coupled to the remote monitoring
area 32, in accordance with the preferred embodiment, by way of a
residential phone line 36. One or more conventional switching stations 38
couple the phone line 36 to the CPU 34. Such switching stations 38 are
conventional switching stations commonly employed by the telephone
company.
Within each remote area 32 there is included a field monitoring device
(FMD) 40. The FMD 40 receives periodic signals 42 from an identification
tag 44. These identification signals 42 contain information that uniquely
identifies the tag 44 from which the signal originates, and that indicates
the status of the circuits internal to the tag, and especially whether
such circuits have sensed an attempt to remove the tag.
Depending upon the particular characteristics of the remote monitoring area
32, the system may also include a repeater 46 that can be selectively
positioned within the area 32. The purpose of the repeater 46 is to
receive the identification signals 42 from the tag 44 and retransmit these
signals, after a short delay, to the FMD 40, to eliminate dead spots. Such
retransmitted signals are identified in FIG. 1 as signals 42'.
While only one tag 44 is shown within the remote monitoring area 32 of FIG.
1, the system of the invention contemplates that a plurality of tags 44
within the monitoring area 32 could be monitored by the same FMD 40, each
tag generating its own unique identification signal at periodic intervals.
The CPU 34 can be coupled through the telephone switching network 38 to a
large number of remote monitoring areas. As will be explained below, the
CPU 34 will typically randomly poll each of the remote monitoring areas
with which it can establish a communication link. Coupled to the CPU 34 is
at least one terminal 48 that provides a means for the CPU 34 to display
the status of the various remote monitoring areas to which it is coupled,
as well as to provide an operator the means for entering data or
instructions into the CPU. Such terminals 48 are common in the art,
typically including a CRT display screen and a keyboard. Also coupled to
the CPU 34 is a printer 50 that can be used to print status reports and
other information concerning the operation of the house arrest monitoring
system 30. Some sample reports generated by the CPU 34 are contained in
Appendix B.
Referring next to FIGS. 2, 3A and 3B, there are shown perspective views of
the tag 44 and the FMD 40 that are used within the remote monitoring area
32. The tag 44, as best shown in FIG. 2, includes a case or housing 52 and
a connecting strap 54. The tag 44 is designed to be worn around a limb,
such as an ankle 56, of its wearer, as shown in FIG. 3A. As explained more
fully below, the housing 52 is designed to be comfortably worn against the
skin or flesh of its wearer. The tag is worn with just enough tension in
the strap 54 to securely hold the housing 52 near the skin or flesh of the
person being monitored. Advantageously, the case 52 is made from a
material that is impervious to the normal kinds of fluids with which the
case may come in contact, such as water, thereby allowing the tag to be
worn at all times. As will be explained more fully below, the only
requirement to the user is that the tag be held near his or her flesh.
Otherwise, a tamper condition will be detected by the circuits within the
tag 44.
The case 52 is made from polystyrene, a type of plastic that is hard and
durable. In the preferred embodiment, the tag measures no more than three
inches square by one inch thick. It weighs less than eight ounces. The
straps 54 are made from a commercially available conductive material.
In FIG. 3B, a perspective view of the FMD 40 and receiver 124 is shown. The
FMD 40 is totally self contained. It is housed in a low profile package or
housing 58 that is simple, unobstrusive, and that easily blends into the
environment of a typical household. The FMD 40 contains no visible dials
or controls that are accessible to those in the household. However, it
does include appropriate lights or other indicators to indicate the
operating status thereof. Two antennas, 60 and 62, are connected to the
receiver 124 which is attached to the FMD 40. These antennas comprise a
length of wire that may be hung or draped down behind the unit in a
location that is not visible to the casual observer. Also available at the
rear of the device is a power line cord 64 and a phone line cord 66. The
power line cord 64 includes a twenty-four (24) volt transformer 68 for
plugging into a standard 110 volt AC outlet socket. Similarly, the phone
line cord 66 may contain a standard quick-connect modular phone jack 70 of
the type used for connecting conventional telephones to a telephone line.
Alternatively, special retainers may be employed in conjunction with the
conventional plugs 68 and 70, and their corresponding sockets, which
retainers can only be removed with an appropriate tool or key, and which
are wired into the tamper circuits of the FMD 40 (so that any attempt to
remove the retainers in order to unplug either the transformer or phone
jack signals a tamper condition).
THE TAG
Referring next to FIG. 4, a block diagram of the circuits within the
identification tag is shown. A low power circuit 80 serves as an
oscillator to provide a basic clock signal for operation of the circuit.
Counter circuit 82 count the ocurrence of clock cycles in order to
regulate the time at which an identification signal 42 is transmitted from | | |
