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Claims  |
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What is claimed is:
1. A personal alarm system, comprising:
a remote unit including radio transmitting means and radio receiving means;
the remote unit transmitting means being able to transmit at more than one
power level and defining a higher power level;
a base station including radio transmitting means and radio receiving
means;
the remote unit and the base station being in radio communication and
defining a separation distance between the remote unit and the base
station;
measuring means for determining whether the separation distance exceeds a
predetermined limit;
means responsive to the measuring means for causing the remote unit
transmitting means to transmit at the higher power level when the
separation distance exceeds the limit; and
alarm means for indicating when the separation distance exceeds the limit.
2. The personal alarm system as set forth in claim 1, wherein the remote
unit includes the measuring means and the means for causing radio
transmission at the higher power level.
3. The personal alarm system as set forth in claim 2, wherein the alarm
means further includes means for the remote unit to communicate to the
base station that transmission is at the higher power level, and base
station means responsive to the communication for providing an alarm.
4. The personal alarm system as set forth in claim 1, wherein the base
station includes the measuring means and the alarm means, and wherein the
means for causing transmission at the higher power level further includes
means for the base station to communicate to the remote unit that
transmission is to be at the higher power level, and remote unit means
responsive to the communication for enabling transmission at the higher
power level.
5. The personal alarm system as set forth in claim 1, wherein the measuring
means includes one radio receiving means defining a received signal
strength, the one radio receiving means including threshold means for
determining whether the field strength falls below a predetermined
threshold, the measuring means defining an equivalence between the field
strength falling below the threshold, and the separation distance
exceeding the limit.
6. The personal alarm system as set forth in claim 1, wherein the remote
unit further includes at least one sensor means for detecting a personal
hazard, the remote unit also including means for communicating a detected
hazard to the base station, and the base station including means
responsive to the communication for giving an alarm.
7. The personal alarm system as set forth in claim 6, wherein the remote
unit includes a plurality of hazard sensors and means for communicating
detected hazards to the base station.
8. The personal alarm system as set forth in claim 6, further including a
plurality of remote units, each remote unit including means for
communicating identification information to the base station, and the base
station including means responsive to the communication for recognizing a
communication as received from a particular remote unit.
9. The personal alarm system as set forth in claim 6, wherein the sensor
means detects immersion in water.
10. The personal alarm system as set forth in claim 6, wherein the sensor
means detects smoke.
11. The personal alarm system as set forth in claim 6, wherein the sensor
means defines a normal range and detects temperatures outside the normal
range.
12. The personal alarm system as set forth in claim 6, wherein the sensor
means defines a dangerous concentration of carbon monoxide and detects the
presence of carbon monoxide exceeding the dangerous concentration.
13. The personal alarm system as set forth in claim 6, wherein the sensor
means defines and detects a dangerous electrical shock hazard.
14. The personal alarm system as set forth in claim 1, wherein the remote
unit includes manually operated switch means and means for communicating
the switch operation to the base station, and the base station includes
means responsive to the communication for giving an alarm.
15. The personal alarm system as set forth in claim 1, wherein the remote
unit includes battery means for deriving operating power, and further
includes means for determining that the power level of the battery means
has fallen below a predetermined power level, the remote unit also
including means for communicating the low battery power to the base
station, and the base station including means responsive to the
communication for giving an alarm.
16. The personal alarm system as set forth in claim 15, wherein the remote
unit includes means for enabling transmission at the higher power level
when low battery power is detected.
17. The personal alarm system as set forth in claim 1, wherein the base
station includes means for initiating a phone call for alerting a
caretaker upon the occurrence of a predetermined event.
18. The personal alarm system as set forth in claim 1, wherein the base
station includes means for obtaining operating power from a vehicle
electrical system.
19. The personal alarm system as set forth in claim 1, including means for
the remote unit giving a loud audible alarm upon command from the base
station.
20. The personal alarm system as set forth in claim 1, wherein the remote
unit is contained within a tamper resistant enclosure and is battery
operated, the enclosure having means for attachment to clothing.
21. The personal alarm system as set forth in claim 20, further including
means for giving an alarm if the remote unit is tampered with or is
removed from the clothing.
22. The personal alarm system as set forth in claim 1; wherein the base
station includes means for deriving operating power from a standard
household electrical outlet.
23. The personal alarm system as set forth in claim 1, wherein the base
station transmits to the remote unit at predetermined intervals and the
remote unit includes means for giving an alarm if the base station fails
to transmit within an interval slightly longer than the predetermined
interval.
24. The personal alarm system as set forth in claim 1, wherein the base
station transmits at predetermined intervals, and the remote unit
transmitting means switches to the higher power level if a base station
transmission is not received within an interval slightly longer than the
predetermined interval.
25. A personal alarm system, comprising:
a remote unit including remote radio transmitting means and remote radio
receiving means;
a base station including local radio transmitting means and local radio
receiving means;
the remote unit and the base station being in radio communication;
the remote unit including global positioning system receiver means for
providing the location of the remote unit in global positioning system
coordinates;
the remote unit further including at least one sensor means for detecting a
personal hazard, the at least one sensor means providing a first output
signal;
the remote radio transmitting means connected to receive the global
positioning coordinates for radio transmission of the coordinates, and the
remote radio transmitting means defining a sensor status and connected to
receive the first output signal for radio transmission of the sensor
status;
the base station including means responsive to global positioning
coordinates received by the local radio receiving means for displaying the
coordinates; and
the base station including means responsive to the sensor status received
by the local receiving means for displaying the sensor status, and for
giving an alarm,
whereby, a detectable emergency will cause the emergency to be identified
to a base station operator and the base station will display the
coordinates of the transmitting remote unit.
26. The personal alarm system as set forth in claim 25, further defining
the global positioning receiver means having a low power standby mode and
a normal operating mode, and the alarm system further including means for
causing the global positioning receiver means to switch from the standby
mode to the normal operating mode upon the detection of a hazard.
27. The personal alarm system as set forth in claim 26, including means for
causing the global positioning receiver means to switch between the low
power standby and the normal operating modes upon command from the base
station.
28. The personal alarm system as set forth in claim 25, wherein the at
least one sensor means includes means for detecting emersion of the remote
unit in water.
29. The personal alarm system as set forth in claim 25, wherein the at
least one sensor means includes means for detecting excessive heat.
30. The personal alarm system as set forth in claim 25, wherein the at
least one sensor means includes means for detecting electrical shock, said
sensor means equipped with a pair of electrical contacts for attachment to
the body of a user for measuring an electrical potential between the
attached contacts.
31. The personal alarm system as set forth in claim 25, further defining a
dangerous carbon monoxide concentration and including a carbon monoxide
sensor having an output signal, the remote radio transmitting means being
connected to receive the carbon monoxide sensor output signal for radio
transmission of a carbon monoxide sensor status.
32. The personal alarm system as set forth in claim 25, wherein the remote
unit transmitting means is able to transmit at more than one power level
and defining a higher power level, and defining a separation distance
between the remote unit and the base station, and the alarm system
including measuring means for determining whether the separation distance
exceeds a predetermined limit and means responsive to the measuring means
for causing the remote unit transmitting means to transmit at the higher
power level when the separation distance exceeds the limit, and alarm
means for indicating when the separation distance exceeds the limit.
33. The personal alarm system as set forth in claim 25, wherein the remote
unit transmits an ID to the base station at predetermined intervals and
wherein the base station includes means for giving an alarm if the remote
unit fails to transmit the ID within an interval slightly longer than the
predetermined interval.
34. A personal alarm system, comprising:
a remote unit including remote radio transmitting means and remote radio
receiving means;
a base station including local radio transmitting means and local radio
receiving means;
the remote unit and the base station being in radio communication;
the remote unit including electrical shock sensor means and providing an
output signal to the remote :radio transmitting means, the sensor
including a pair of electrical contacts for connection to the body of a
user; and
the remote radio transmitting means being adapted to transmit when the
sensor detects an excessive electrical potential between the electrical
contacts;
the base station including means responsive to the transmission from the
remote unit for giving an alarm,
whereby an alarm can be given if the electrical shock hazard is detected. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to personal alarm systems and in particular to such
systems transmitting at a higher power level during emergencies.
2. Background Art
Personal alarm systems are well known in the art (see for example U.S. Pat.
Nos. 4,777,478, 5,025,247, 5,115,223, 4,952,928, 4,819,860, 4,899,135,
5,047,750, 4,785,291, 5,043,702, and 5,086,391). These systems are used to
maintain surveillance of children. They are used to monitor the safety of
employees involved in dangerous work at remote locations. They are even
used to find lost or stolen vehicles and strayed pets.
These systems use radio technology to link a remote transmitting unit with
a base receiving and monitoring station. The remote unit is usually
equipped with one or more hazard sensors and is worn or attached to the
person or thing to be monitored. When a hazard is detected, the remote
unit transmits to the receiving base station where an operator can take
appropriate action in responding to the hazard.
The use of personal alarm systems to monitor the activities of children has
become increasingly popular. A caretaker attaches a small remote unit, no
larger than a personal pager, to an outer garment of a small child. If the
child wanders off or is confronted with a detectable hazard, the caretaker
is immediately notified and can come to the child's aid. In at least one
interesting application, a remote unit includes a receiver and an audible
alarm which can be activated by a small hand-held transmitter. The alarm
is attached to a small child. If the child wanders away in a large crowd,
such as in a department store, the caretaker actives the audible alarm
which then emits a sequence of "beeps" useful in locating the child in the
same way one finds a car at a parking lot through the use of an auto alarm
system.
A number of novel features have been included in personal alarm systems.
Hirsh et al., U.S. Pat. No. 4,777,478, provide for a panic button to be
activated by the child, or an alarm to be given if someone attempts to
remove the remote unit from the child's clothing. Banks, U.S. Pat. No.
5,025,247, teaches a base station which latches an alarm condition so that
failure of the remote unit, once having given the alarm, will not cause
the alarm to turn off before help is summoned. Moody, U.S. Pat. No.
5,115,223, teaches use of orbiting satellites and triangulation to limit
the area of a search for a remote unit which has initiated an alarm. In
U.S. Pat. No. 4,952,928 to Carroll et al., and in U.S. Pat. No. 4,819,860
to Hargrove et al., the apparatus provides for the remote monitoring of
the vital signs of persons who are not confined to fixed locations.
Ghahariiran, U.S. Pat. No. 4,899,135, teaches a child monitoring device
using radio or ultra-sonic frequency to give alarm if a child wanders out
of range or falls into water. Hawthorne, U.S. Pat. 4,785,291, teaches a
distance monitor for child surveillance in which a unit worn by the child
includes a radio transmitter. As the child moves out of range, the
received field strength, of a signal transmitted by the child's unit,
falls below a limit and an alarm is given.
Clinical experience in the emergency rooms of our hospitals has taught that
a limited number of common hazards account for a majority of the
preventable injuries and deaths among our toddler age children. These
hazards include the child's wandering away from a safe or supervised area,
water emersion, fire, smoke inhalation, carbon monoxide poisoning and
electrical shock. Child monitoring devices, such as those described above,
have been effective in reducing the number of injuries and deaths related
to these common preventable hazards.
However, considering the importance of our children's safety, there remains
room for improvement of these systems. One such area for improvement
relates to increasing the useful life of a battery used to power the
remote unit of these toddler telemetry systems, as they have come to be
called.
The remote unit is typically battery operated and, in the event of an
emergency, continued and reliable transmission for use in status reporting
and direction finding is of paramount importance. In other words, once the
hazard is detected and the alarm given, it is essential that the remote
unit continue to transmit so that direction finding devices can be used to
locate the child.
The remote unit of most child monitoring systems is typically quite small
and the available space for a battery is therefore quite limited. Despite
recent advances in battery technology, the useful life of a battery is
typically related to the battery size. For example, the larger "D" cell
lasting considerably longer than the much smaller and lighter "AAA" cell.
Though the use of very low power electronic circuits has made possible the
use of smaller batteries, a battery's useful life is still very much a
factor of its physical size, which, as stated above, is limited because of
the small size of a typical remote unit. Therefore, additional efforts to
reduce battery drain are important.
Given that much reliance is placed on the reliability of any child
monitoring system, it would be desirable for the remote unit to transmit
at a low power or not at all when no danger exists. In this way battery
life is increased and system reliability is improved overall, since the
hazards are usually the exception rather than the rule.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a personal alarm system
in which the battery operated remote unit normally transmits at low power
and switches to a higher power when the distance between the remote unit
and base station exceeds a predetermined limit.
It is also an object of the present invention to provide such a system
which includes sensors for the hazardous conditions typically confronting
young children.
It is a further object of the present invention to provide such a personal
alarm system which includes a periodic handshake exchange between the
remote unit and base station to demonstrate that the system continues to
be operational.
In accordance with the above objects and those that will become apparent
below, a personal alarm system is provided, comprising:
a remote unit including radio transmitting means and radio receiving means;
the remote unit transmitting means being able to transmit at more than one
power level and defining a higher power level;
a base station including radio transmitting means and radio receiving
means;
the remote unit and the base station being in radio communication and
defining a separation distance between the remote unit and the base
station;
measuring means for determining whether the separation distance exceeds a
predetermined limit;
means responsive to the measuring means for causing the remote unit
transmitting means to transmit at the higher power level when the
separation distance exceeds the limit; and
alarm means for indicating when the separation distance exceeds the limit.
In one embodiment of the invention, the base station transmits a periodic
polling signal and the remote unit monitors the field strength of the
received polling signal. If the received field strength falls below a
limit, corresponding to some maximum distance between the two devices, the
remote unit transmits at high power. The signal transmitted at high power
includes an indication that transmission is at high power. When this
signal is received by the base station, an alarm is given. The remote unit
also is equipped to detect one or more hazards.
In another embodiment of the invention, there are multiple remote units
each able to identify itself by including a unit identification number in
its transmitted signal. The remote unit is equipped to detect one or more
hazards and to identify detected hazards in its transmission. The base
station is able to display the transmitting unit identification number and
the type of any detected hazard.
In another embodiment, the base station, rather than the remote unit,
measures the field strength of the received remote unit transmission and
instructs the remote unit to transmit at high power when the received
field strength falls below a preset limit.
In another embodiment, the remote unit includes both visual and audible
beacons which can be activated by the base station for use in locating the
child.
In another embodiment, the remote unit includes a panic button which the
child or concerned person can use to summon help.
In another embodiment, the base station includes the ability to initiate a
phone call via the public telephone system, for example by initiating a
pager message to alert an absent caretaker.
In another embodiment, the remote unit includes a global positioning system
("GPS") receiver which is activated if a hazard is detected or if the
child wanders too far from the base station. The remote unit then
transmits global positioning coordinates from the GPS receiver. These
coordinates are received by the base station and used in locating the
child. In an alternative embodiment, the remote unit is attached to a
child, pet or vehicle and the GPS receiver is activated by command from
the base station. The global positioning coordinates are then used by the
base station operator to locate the remote unit.
In another embodiment, the remote unit is worn by an employee doing
dangerous work at a remote location such as an electrical power lineman
repairing a high voltage power line. The remote unit is equipped with a
GPS receiver and an electrical shock hazard sensor and the remote unit
will instantly transmit the workman's location in the event of electrical
shock. The device will permit an emergency medical crew to rapidly find
and give aid to the injured workman and possibly save a life.
It is an advantage of the present invention to periodically test system
integrity by exchanging an electronic handshake and giving an alarm in the
event of failure.
It is also an advantage of the present invention to prolong the remote unit
battery life by transmission at low power in the absence of a defined
emergency.
It is also an advantage of the present invention that the system is able to
detect and give alarm for a number of common and dangerous hazards.
It is a further advantage of the present invention to permit rapid and
precise location of the remote unit which is equipped with a GPS receiver.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a block diagram of a personal alarm system in accordance with one
embodiment of the present invention and transmitting at selectable power
levels.
FIG. 2 is a block diagram of another embodiment of the personal alarm
system illustrated in FIG. 1 including multiple remote units.
FIG. 3 is a block diagram illustrating another embodiment of the personal
alarm system in accordance with the present invention.
FIG. 4 is a pictorial diagram illustrating a preferred message format used
by the personal alarm system illustrated in FIG. 2.
FIG. 5 is a pictorial diagram illustrating another preferred message format
used by the personal alarm system illustrated in FIG. 2.
FIG. 6 is a block diagram illustrating an embodiment of the personal alarm
system of the present invention using the Global Positioning System to
improve remote unit location finding.
FIG. 7 is a pictorial diagram illustrating a base station and remote unit
of the personal alarm system of FIG. 1, in a typical child monitoring
application.
FIG. 8 is a pictorial diagram illustrating a remote unit in accordance with
the present invention being worn at the waist.
FIG. 9 is a pictorial diagram illustrating a mobile base station in
accordance with the present invention for operation from a vehicle
electrical system.
FIG. 10 is a pictorial diagram illustrating a base station in accordance
with the present invention being operated from ordinary household power.
DETAILED DESCRIPTION OF THE INVENTION
With reference to FIG. 1, there is shown a block diagram of a personal
alarm system according to one embodiment of the present invention and
depicted generally by the numeral 10. The personal alarm system 10
includes a remote unit 12 and a base station 14. The remote unit 12 has a
radio transmitter 16 and a receiver 18, and the base station 14 has a
radio transmitter 20 and a receiver 22. The transmitters 16, 20 and
receivers 18, 22 are compatible for two-way radio communication between
the remote unit 12 and the base station 14.
In a preferred embodiment, the base station 14 includes an interval timer
24 which causes the transmitter 20 to transmit at predetermined intervals.
The receiver 18 of the remote unit 12 receives the signal transmitted by
the base station 14 and causes the transmitter 16 to transmit a response
to complete an electronic handshake.
The remote unit transmitter 16 is capable of transmitting at an energy
conserving low-power level or at an emergency high-power level. When the
distance between the remote unit 12 and the base station 14 exceeds a
predetermined limit, the remote unit responds at the higher power level.
To accomplish the shift to the higher power level, the remote unit receiver
18 generates a signal 26 which is proportional to the field strength of
the received signal, transmitted by the base station 14. The remote unit
12 includes a comparator 23 which compares the magnitude of the field
strength signal 26 with a predetermined limit value 30 and generates a
control signal 32.
The remote unit transmitter 16 is responsive to a circuit 34 for selecting
transmission at either the low-power level or at the high-power level. The
circuit 34 is connected to the control signal 32 and selects transmission
at the low-power level when the received field strength equals or exceeds
the limit value 30, and at the higher power level when the received field
strength is less than the limit value 30. Alternatively, the remote unit
transmitter 16 transmits at one of a selectable plurality of transmission
power levels. In another alternative embodiment, transmission is
selectable within a continuous range of transmission power levels.
Within an operating range of the personal alarm system 10, the field
strength of the base station 14 transmitted signal when received at the
remote unit 12 is inversely proportional to the fourth power
(approximately) of the distance between the two units. This distance
defines a `separation distance,` and the predetermined limit value 30 is
selected to cause transmission at the higher power level at a desired
separation distance within the operating range.
In another embodiment, the remote unit 12 includes a hazard sensor 36 which
is connected to the transmitter 16. The hazard sensor 36 is selected to
detect one of the following common hazards, water emersion, fire, smoke,
excessive carbon monoxide concentration, and electrical shock. In one
embodiment, a detected hazard causes the remote unit 12 to transmit a
signal reporting the existence of the hazardous condition at the moment
the condition is detected. In another embodiment, the hazardous condition
is reported when the response to the periodic electronic handshake occurs.
In one embodiment, the base station 14 includes an audible alarm 38 which
is activated by the receiver 22. If the remote unit fails to complete the
electronic handshake or reports a detected hazard or indicates it is out
of range by sending an appropriate code, the base station alarm 38 is
activated to alert the operator.
FIG. 2 is a block diagram illustrating another embodiment of the personal
alarm system of the present invention. The alarm system is indicated
generally by the numeral 40 and includes a first remote unit 42, a second
remote unit 44 and a base station 46. The first remote unit 42 includes a
transmitter 48, a receiver 50, an identification number 52, a received
field strength signal 54, a comparator 56, a predetermined limit value 58,
a control signal 60, a power level select circuit 62 and a hazard sensor
64.
The second remote unit 44 includes a separate identification number 66, but
is otherwise identical to the first remote unit 42.
The base station 46 includes a transmitter 68, an interval timer 70, a
receiver 72, an alarm 74 and an ID-Status display 76.
In one embodiment of the invention illustrated in FIG. 2, the radio
transmission between the first remote unit 42 and the base station 46
includes the identification number 52. The transmission between the second
remote unit 44 and the base station 46 includes the identification number
66. It will be understood by those skilled in the art that the system may
include one or more remote units, each having a different identification
number 52.
It will also be understood that each remote unit 42 may have a different
predetermined limit value 58. The limit value 58 defines a distance
between the remote unit 42 and the base station 46 beyond which the remote
unit will transmit at its higher power level. If a number of remote units
are being used to monitor a group of children, in a school playground for
example, the limit values of each remote unit may be set to a value which
will cause high power transmission if the child wanders outside the
playground area. In other applications, the limit value 58 of each remote
unit 42 may be set to a different value corresponding to different
distances at which the individual remote units will switch to high power
transmission.
In one embodiment, the base station 46 will provide an alarm 74 whenever a
remote unit transmits at high power or reports the detection of a hazard.
The identification number of the reporting remote unit and an indication
of the type of hazard is displayed by the base station on the ID-Status
display 76. This information can be used by the operator, for example a
day-care provider, to decide what response is appropriate and whether
immediate caretaker notification is required. If a child has merely
wandered out of range, the provider may simply send an associate out to
get the child and return her to the play area. On the other hand, a water
emersion hazard indication should prompt immediate notification of
caretakers and emergency personnel and immediate action by the day-care
employees.
In another embodiment, the remote unit receiver 50 determines that the
separation distance between the remote unit 42 and the base station 46
exceeds the predetermined threshold. The remote unit transmitter 48
transmits a code or status bit to indicate that fact.
In an embodiment illustrated in FIG. 1, the polling message transmitted
periodically by the base station 14 is an RF carrier. The carrier
frequency is transmitted until a response from the remote unit 12 is
received or until a watchdog timer (not illustrated) times out, resulting
in an alarm. The information contained in the remote unit response must
include whether transmission is at low power or at high power, and whether
a hazard has been detected, since the base station provides an alarm in
either of these instances.
In an embodiment illustrated in FIG. 2, however, additional information
must be reported and the advantages of a digitally formatted remote unit
response will be apparent to those possessing an ordinary level of skill
in the art.
FIG. 3 is a block diagram illustrating another embodiment of the personal
alarm system in accordance with the present invention and generally
indicated by the numeral 80. Personal alarm system 80 includes a remote
unit 82 and a base station 84.
The remote unit 82 includes a transmitter 86, a receiver 88, a power level
select circuit 90, an ID number 92, a visual beacon 94, an audible beacon
96, a watchdog timer 98, a plurality of hazard sensors 100 including a
water emersion sensor 102, a smoke sensor 104, a heat sensor 106, a carbon
monoxide sensor 108, a tamper switch 109, and an electrical shock sensor
110, an emergency switch ("panic button") 112, a battery 113, and a `low
battery power` sensor 114.
The base station 84 includes a transmitter 116, a receiver 118 which
produces a received field strength signal 120, a comparator 122, a
predetermined limit value 124, a comparator output signal 126, an interval
timer 128, control signals 130 and 132, a visual alarm 134, an audible
alarm 136, an ID and Status display 138, a circuit 140 for initiating a
phone call and a connection 142 to the public telephone system.
The base station 84 and a plurality of the remote units 82 illustrated in
the embodiment of FIG. 3 communicate using a digitally formatted message.
One message format is used by the base station 84 to command a specific
remote unit 82, and a second message format is used by a commanded remote
unit 82 to respond to the base station 84. These message formats are
illustrated in FIGS. 5 and 4, respectively.
With reference to FIG. 4 there is shown a pictorial diagram of a preferred
digital format for a response from a remote unit in a personal alarm
system in accordance with the present invention, indicated generally by
the numeral 150. The digital response format 150 includes a remote unit ID
number 152, a plurality of hazard sensor status bits 154 including a water
emersion status bit 156, a smoke sensor status bit 158, a heat sensor
status bit 160, an excessive carbon monoxide concentration status bit 162,
and an electrical shock status bit 164. The response 150 also includes a
high power status bit, 166, a panic button status bit 168, a low battery
power detector status bit 170, a tamper switch status bit 171, and bits
reserved for future applications 172.
FIG. 5 is a pictorial diagram of a preferred digital format for a base
station to remote unit transmission, generally indicated by the numeral
180. The digital message format 180 includes a command field 182 and a
plurality of unassigned bits 190 reserved for a future application. The
command field 182 includes a coded field of bits 184 used to command a
specific remote unit to transmit its response message (using the format
150). The command field 182 also includes a single bit 186 used to command
a remote unit, such as the embodiment illustrated in FIG. 3, to transmit
at high power. The command field 182 includes command bit 188 used to
command a remote unit to activate a beacon, such as the visual beacon 94
and the audible beacon 96 illustrated in FIG. 3 | | |
