Apparatus and method for monitoring cellular telephone usage

A small, wireless, battery operated monitoring apparatus is provided that is installed by a user on a cellular telephone in close proximity to a telephone antenna. The monitoring device monitors telephone usage by detecting and tracking radio frequency signal transmissions from the antenna to a base station. The monitoring device includes a microprocessor that performs functions on data indicative of cellular telephone usage and the customer billing plan. The microprocessor, under control of a call processing program, determines exactly when cellular mobile service is established and terminated at the cellular telephone. Under control of a time tracking program, the microprocessor monitors telephone usage, and generates statistical information indicative of telephone usage. The tracking program allows the user to set parameter values associated with statistical information indicative of a customer billing plan and the current date and time. The microprocessor maintains and updates the statistical information, as necessary. The current parameter values for the statistical information generated by the microprocessor are selectively displayed on a display unit associated with the monitoring device. The monitoring device can be used with any manufacturer's cellular telephone, and works with any cellular telephone system standard in the United States or abroad. An alternative embodiment of the present invention allows for the monitoring device to be incorporated into the standard electrical circuitry associated with a cellular telephone such that at least a portion of the monitoring apparatus is contained within the housing of the mobile unit. A method for monitoring telephone usage is also disclosed.

BACKGROUND OF THE INVENTION 
This invention relates generally to wireless communications systems and, 
more specifically, to a method and apparatus for monitoring and displaying 
current and cumulative usage data for cellular mobile telephone service 
provided during a billing period. 
The use of cellular telephones has increased dramatically over the last few 
years. Subscribers to cellular telephone service generally are billed for 
the time the telephone is in use. Novel or creative billing packages are 
employed by the cellular service providers as marketing tools. 
Often the billing packages include a combination of rates. For example, the 
service may offer unlimited free off-peak time, limited free off-peak, 
reduced rates for different times of the day, graduated rates based upon 
volume usage and so forth. It will be appreciated that regardless of the 
billing package employed, the telephone user has a keen interest in 
tracking the amount of time the telephone is in use, for obvious reasons. 
Most cellular telephones have a simple built-in timer that indicates the 
duration of the last call or the total usage since the timer was last 
reset. These simple timers are of little utility to the user who wishes to 
track his or her monthly peak or off-peak usage. The user may want to 
track the total number of peak minutes used in a given billing period. 
Likewise, the user may want to track the usage in terms of total dollars 
rather than minutes of air time. With primitive timers, the user may 
receive an unexpectedly large bill at the end of the month. 
The user also may want to track the remaining balance of free minutes. For 
example, the user may forego using the telephone at certain times of the 
day for fear of going over budget when, in reality, the user still has 
unused free or reduced rate time available in the billing period. 
In other applications, the owner of the cellular telephone may want to bill 
a third party for use of the telephone. For example, if the telephone is 
rented on a short term basis or mounted in a rental car the owner of the 
telephone would benefit from a quick and accurate readout of total time 
the phone was in use or total charges incurred by the use of the phone. 
U.S. Pat. No. 5,233,642, to Renton, describes a device for this type of 
application. Although the device provides details of each call, it suffers 
from a number of drawbacks. First, it only operates with its own specific 
built-in cellular transceiver. It is not interchangeable between phones. 
It cannot be attached to and transported along with a portable phone. 
Furthermore, it requires an outside power source and is wired to the 
cellular transceiver. The Renton device does not display statistical usage 
information to the user and cannot report actual dollar usage. 
There are more than one dozen types of cellular telephone systems in use 
worldwide. These systems operate at various radio frequencies. For 
example, these systems include the AMPS (Advanced Mobile Phone Service) 
system in use in the United States, Canada, Australia and elsewhere. The 
AMPS system uses mobile to base station frequencies of 825 to 845 MHz. The 
TACS (Total Access Coverage Service) system is used in the United Kingdom, 
United Arab Emirates, China and elsewhere and employs mobile to base 
station frequencies of 890 to 915 MHz. The NMT-450 (Nordic Mobile 
Telephone) system is in use in France, Switzerland, Saudi Arabia and 
elsewhere and uses mobile to base station frequencies of 453 to 457.5 MHz. 
It would be a great advantage to have a device that monitors telephone 
usage at these various frequencies. 
Most cellular telephone systems are analog in nature. The voice signal is 
modulated directly onto a continuous RF carrier. A single subscriber uses 
each RF channel for the duration of the telephone call. There are, 
however, emerging digital cellular standards in which the voice signal is 
first digitized then transmitted in digital form on an RF carrier which is 
discontinuous, i.e., the carrier is turned on only periodically, occupying 
a short time slice which has been dynamically assigned. Such systems 
include IS-54-B, a digital cellular standard, currently in limited use in 
the United States, and which transmits discontinuously with a 33.3% duty 
cycle. IS-95-A, a digital standard, is to be implemented in the United 
States in 1996 and transmits discontinuously with a 12.5% duty cycle. 
Finally, GSM, a digital standard, currently in use in Europe, transmits 
discontinuously with a 12.5% duty cycle. Any device that would monitor 
cellular phone usage should be able to monitor analog and digital 
telephone systems. 
Furthermore, it will be appreciated that all cellular telephone systems 
automatically adjust their RF power levels as required by local 
conditions. Any device used to monitor cellular phone usage should be able 
to dynamically adjust its input sensitivity. The ability to adjust its 
input sensitivity would allow the device to ignore unwanted nearby RF 
signal sources by adjusting to the level of sensitivity needed under the 
conditions. The lowest power level necessary for telephone call detection 
under any of the cellular telephone systems is -22 dBm (6.3 milliwatts). 
In summary, no device is presently available that is wireless or built 
directly into a cellular telephone for monitoring cellular telephone usage 
that can monitor peak, off-peak and connect time or which can display 
usage in terms of dollars, minutes of peak or off-peak time used or 
remaining. There is no device that can keep track of totals for a user's 
monthly billing period or save information from a previous month's use or 
bill. Furthermore, there is no device available that can be used with any 
cellular phone, that can adjust its RF detection sensitivity or can be 
used with various mobile unit systems. 
SUMMARY OF THE INVENTION 
Accordingly, it is among the principal objects of the present invention to 
provide a device for the detailed monitoring and display of cellular 
telephone usage. 
It is another object of the present invention to provide such a device that 
can report the cellular telephone usage in a number of categories 
including total connect time, peak time used, off-peak time used, unused 
peak and off-peak time remaining. 
Still another object of the present invention is to provide such a device 
that stores monthly totals. 
Yet another object of the invention is to provide such a device that can 
employs a broad band antenna and RF detection circuit which allows it to 
be used with any cellular telephone system. 
Another object of the invention is to provide such a device that can be 
used with analog and digital cellular telephone systems. 
A still further object of the invention is to provide such a device that is 
wireless and can be retrofitted to any cellular telephone transceiver. 
Another object of the invention is to provide such a device that is 
economical to manufacture, incorporates a simple long-life battery for 
power, is easy to install and well suited for its intended purposes. 
A further object of the invention is to provide a device for detailed 
monitoring and display of cellular telephone usage that can be 
incorporated into the standard electrical circuitry associated with a 
cellular telephone such that at least a portion of the device is contained 
within the housing of the cellular telephone. 
These and other objects will become apparent to those skilled in the art in 
light of the following disclosure and accompanying drawings. 
In accordance with the invention, generally stated, an apparatus is 
disclosed for monitoring when a cellular telephone is used for mobile 
cellular communications that includes detection means for detecting the 
presence of a telephone call from the cellular telephone. A programmable 
control means tracks the duration and time of day associated with the 
telephone call. The apparatus also includes means for manually inputting 
data into the data processing means indicative of terms of a customer 
billing package and current date and time. The control means maintains and 
updates the data, and generates statistical information based upon the 
data and the duration and time of day of the telephone call. Display means 
is provided for selectively displaying statistical information and a 
function code representative of a particular function performed by the 
control means in generating the displayed statistical information. A power 
source is provided for supplying power to the control means. 
Another aspect of the present invention is of a device for monitoring usage 
of a cellular telephone based upon RF signal transmissions from an antenna 
associated with the cellular telephone that includes detection means for 
detecting the presence of RF signal transmissions from the cellular 
telephone, and generating an output signal representative of transmitted 
RF signals. Data processing means is operatively connected to the 
detection means. The data processing means generates a reference signal 
having a preselected magnitude. The data processing means tracks the 
duration and timing of the output signal generated by the detection means 
having a magnitude greater than or equal to the magnitude of the reference 
signal for a period of time exceeding a predetermined time interval. The 
data processing means performs input, processing, storage, output and 
control functions to accomplish a sequence of operations on data stored 
therein, and to generate statistical information indicative of cellular 
telephone usage based upon RF signal transmissions from the cellular 
telephone. Means is provided for manually inputting data into the data 
processing means. Display means displays one of a plurality of function 
codes representative of a particular function performed by the data 
processing means in generating the displayed statistical information and 
the statistical information associated with the displayed function code. 
Means is provided for selectively viewing any one of the plurality of 
function codes and associated statistical information by manually 
advancing the statistical information and function code displayed on the 
display means. A power source supplies power to the data processing means. 
Still another aspect of the present invention is that of a wireless 
monitoring device for monitoring when a cellular telephone is used for 
mobile cellular telephone service. The device includes an RF detection 
circuit including a broadband antenna coupled to an antenna associated 
with the cellular telephone for detecting RF signal transmission from the 
telephone antenna, and generating an analog output voltage proportional to 
transmitted RF signals. A microprocessor is provided for controlling the 
operation of the monitoring device and processing data indicative of usage 
of the cellular telephone. The microprocessor includes call processing 
means for determining whether the cellular telephone is in use, and time 
tracking means for monitoring duration and timing of the telephone call. 
The microprocessor generates a digital output signal that is supplied to a 
digital to analog (D/A) converter. The D/A converter generates an analog 
reference voltage that is proportional to the digital output signal 
generated by the microprocessor having a threshold voltage level at or 
above which the voltage level of the output voltage generated by the RF 
detection circuit must be maintained for the monitoring device to consider 
the cellular telephone to be in use. An analog comparator has a first 
input coupled to the output voltage generated by the RF detection circuit 
and a second input coupled to the analog reference signal generated by the 
D/A converter. The comparator generates a digital output signal having a 
first state when the first input is less than the second input, and a 
second state when the first input is greater than or equal to the second 
input. The output signal generated by the comparator is supplied to the 
microprocessor. A clock is coupled to the microprocessor for generating a 
clock pulse to provide for synchronization of functions performed by the 
microprocessor. A display unit allows for individually displaying a 
plurality of parameter values stored in the microprocessor corresponding 
to data processed by the microprocessor. First user actuated switching 
means is connected to the microprocessor for incrementally varying 
displayed parameter values. Second user actuated switching means is also 
connected to the microprocessor for advancing the displayed parameter 
values to the next parameter value stored in the microprocessor. A power 
source is provided for supplying power to the microprocessor. 
Yet another aspect of the present invention is that of a method for 
monitoring the duration and timing of RF signal transmissions from a 
cellular phone during a cellular telephone call, comprising the steps of: 
manually setting the current day of the week, day of the month, month and 
year; 
detecting the presence of RF signal transmissions from a cellular 
telephone; 
generating a first signal representative of RF signal transmissions; 
generating a variable reference signal having a minimum threshold voltage 
level; 
determining whether the first signal is maintained at a voltage level 
greater than or equal to the minimum threshold voltage level for a first 
predetermined time interval; 
triggering a second predetermined time interval when the first signal is 
maintained at the voltage level greater than or equal to the minimum 
threshold voltage level for the first predetermined time interval; 
establishing the presence of a telephone call from the cellular telephone 
when RF signal transmissions are detected after the expiration of the 
second time interval; 
monitoring the duration and timing of the cellular telephone call; 
generating statistical information indicative of usage of the cellular 
telephone based upon the manually set parameter values and the duration 
and timing of all telephone calls made from the cellular telephone during 
a predetermined time interval; 
displaying statistical information on a visual display; 
triggering a third predetermined time interval when RF signal transmissions 
are not detected after the expiration of the second time interval; 
continuing to monitor the duration and timing of the cellular telephone 
call when RF signal transmissions are detected after the expiration of the 
third time interval; and 
terminating the telephone call when RF signal transmissions are not 
detected after the expiration of the third time interval. 
Other objects and features will be apparent and in part pointed out 
hereinafter.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIG. 1, there is shown a monitoring device, indicated 
generally at 1, attached to a conventional cellular mobile telephone or 
mobile unit 2 in close proximity to a cellular telephone antenna 3 
associated with the mobile unit 2. The mobile unit 2 communicates by 
two-way radio with a local cellular base station 4. The monitor 1 detects 
and monitors radio frequency (RF) transmission from the mobile unit 2 to 
the base station 4. 
FIG. 2 best illustrates the internal electrical circuitry and hardware of 
monitor 1. Monitor 1 employs a controller or microcontroller which acts as 
a data processing device by performing a plurality of input, processing, 
storage, output and control functions to accomplish a sequence of 
operations on data indicative of cellular telephone usage and the terms of 
a customer billing plan that is stored in the controller. The controller 
is preferably a microprocessor 5 operating under programmed control as 
shown in FIG. 2. Certain microprocessor functions are controlled by either 
a call processing program or a time tracking program stored in the 
microprocessor 5. The microprocessor 5, under control of the call 
processing program, determines exactly when cellular mobile telephone 
service is established and terminated at the mobile unit 2 (see FIG. 3). 
Under control of the time tracking program, the microprocessor monitors 
the telephone usage, and generates statistical information indicative of 
telephone usage such as total time used or available free of charge during 
specified time intervals (e.g., peak and off-peak time intervals) in a 
billing period, and the current total cost for total time used in a 
billing period based upon billing rates associated with specified time 
intervals and connection time. The time tracking program also allows the 
user to set parameter values for statistical information indicative of the 
terms of a particular billing plan or package to which the user subscribes 
(e.g., billing rates for different times of a day or week, billing period, 
connection time rates, amount of peak and off peak time available free of 
charge in a billing period). The user can also set parameter values for 
statistical information indicating the current day of the week, day of the 
month, month, year which the microprocessor 5 updates and maintains. As 
discussed below in greater detail, FIG. 4 sets forth a list of statistical 
information that can be generated by the microprocessor time tracking 
program when a user subscribes to a mobile cellular telephone service 
having a billing package with separate billing rates for peak time and 
off-peak time and a set amount of time available free of charge during 
peak and off-peak time for each billing period. It will be appreciated by 
those skilled in the art that the time tracking program easily can be 
altered to accommodate different billing plans having alternative billing 
schemes. 
Synchronization of internal components associated with the microprocessor 5 
is controlled by timing pulses generated by a clock 6 including a crystal 
oscillator. The clock 6 is used to control all internal timings, including 
the time of day and other calendaring functions. The clock 6 allows the 
microprocessor 5 to accurately determine the date and time at which a 
telephone call begins and ends. 
At least one button cell battery 7 such as a standard watch battery 
supplies necessary power to the microprocessor 5, based upon the power 
requirements of the monitoring device 1. A capacitor 8 connected in 
parallel with the cell battery 7 functions as an energy storage element so 
that the microprocessor 5 retains stored statistical information, usage 
data and parameter settings during battery failure or replacement. 
The microprocessor 5 drives a digital display 9 such as a liquid crystal 
display (LCD) that provides a digital readout of alphanumeric symbols 
representative of function codes and statistical information associated 
with various time tracking functions performed by the microprocessor 5. 
The function codes and statistical information associated with each 
function code are stored in the microprocessor 5. One function code and 
its associated statistical information are displayed on the display 9 at 
all times. As will be discussed in greater detail below, the 
microprocessor 5 automatically updates the statistical information 
associated with certain functions, when appropriate. The function code, 
shown on the left side of the display 9 in FIG. 2, indicates a particular 
time tracking function performed by the device 1 or a particular parameter 
setting that is used and maintained by the microprocessor in performing 
the time tracking functions. The statistical information, shown on the 
right side of the display 9 in FIG. 2, includes usage information 
indicative of the current parameter value of cellular telephone usage data 
associated with the displayed function code. The statistical information 
also includes information that does not directly reflect telephone usage 
data, such as the current time of day and the current day of week. This 
type of statistical information may be used by the microprocessor 5 to 
determine certain usage information. The monitoring device 1 can be 
programmed to monitor and display information associated with the use and 
operation of the mobile unit 2. FIG. 4 sets forth a list of possible 
function codes and statistical information that can be displayed on the 
digital display 9. FIG. 4 also includes a brief description of each 
function corresponding to a particular function code which will be 
discussed more fully below. 
The monitoring device 1 also includes two manually operable push button 
switches, namely, a function switch 10 and a parameter value switch 11. 
Each switch 10, 11 has a normally open position and an actuated or closed 
position. The microprocessor 5 periodically examines the position of the 
switches 10, 11. When the function switch 10 is actuated, the 
microprocessor 5 changes or advances the displayed function code to the 
next function code stored in the microprocessor 5. Actuation of the 
parameter value switch 11 causes the microprocessor 5 to change (e.g., 
incrementally increase or decrease) the parameter value of the statistical 
information symbols shown on the display 9, when appropriate if the value 
is changeable. This allows the user to update the statistical information 
associated with various functions, e.g., changing the start date, changing 
the billing rate for peak or off-peak time or changing the current time. 
The microprocessor 5 is responsive to RF signals transmitted from the 
telephone 2 to the cellular base station 4 via the antenna 3 associated 
with the mobile unit 2. The monitoring device 1 includes an RF detection 
circuit 12 having a broadband antenna 13 that is effectively coupled to 
the telephone antenna 3 to detect the presence of RF signal transmissions 
from the antenna 3. The detection circuit 12 is capable of detecting 
continuous or periodic RF signal transmissions so as to allow the 
monitoring device 1 to operate in conjunction with either analog or 
digital cellular telephones. The broadband antenna 13 has a compact design 
so that it is easily contained within the packaging (as shown in FIG. 5) 
of the monitoring device 1. The RF detection sensitivity is adjusted to 
the appropriate level needed under current conditions, thus allowing the 
monitor 1 to ignore unwanted nearby RF signal sources. When RF signal 
transmissions are detected by the antenna 13, the antenna 13 generates a 
RF signal proportional to the transmitted signal. The detection circuit 12 
converts the RF signal to an analog voltage proportional to the RF signal 
level. In the preferred embodiment, the RF detection circuit 12 is capable 
of sensing the RF signals having power levels of -22 dBm (6.3 mW). The 
analog output signal of the RF detector 12 is presented to a first input 
15 of an analog comparator 14. 
A second input 16 of comparator 14 is operatively connected to the 
microprocessor 5 via a digital to analog (D/A) converter 17. More 
specifically, the microprocessor 5 controls RF signal detection 
sensitivity by generating a digital output signal that is supplied to the 
D/A converter 17. The D/A converter 17 generates an analog reference 
signal that is proportional to the digital output signal. The analog 
reference signal has a minimum threshold voltage level at or above which 
the output signal of the RF detection circuit 12 must be maintained before 
the microprocessor 5 performs any time tracking functions monitoring 
cellular telephone usage. The microprocessor 5 effectively adjusts the 
minimum threshold voltage level of the analog reference signal by varying 
its digital output signal, depending upon the type of cellular system 
employed and the timing of the call processing program and associated 
functions. The analog reference signal generated by the D/A converter 17 
is then presented to the second input 16 of the comparator 14. The 
comparator 14 generates a binary output signal having a first state or 
voltage level and a second state or voltage level that is presented to the 
microprocessor 5. 
The output signal of the comparator 14 is maintained in the first state 
when the voltage level of the output signal generated by the RF detection 
circuit 12 is less than the minimum threshold voltage level of the 
reference signal. In this situation, the mobile unit 2 is not in use and 
time tracking functions associated with the microprocessor are 
deactivated. When the voltage level of the RF signal is greater than or 
equal to the minimum threshold level, the output signal of the comparator 
14 changes state so as to be maintained in the second state. As will be 
discussed in greater detail below with respect to FIG. 3, when the output 
signal is maintained in the second state for a predetermined time interval 
(call establishment delay period), the microprocessor 5, under the control 
of the call processing program, activates the time tracking program to 
monitor the time the mobile unit is in use. The time tracking program 
remain activated by the microprocessor 5 until the output signal of the 
comparator 14 changes to the first state for a predetermined time interval 
(hang-up delay period). 
The call processing program for microprocessor 5 used in a TIA-553 (U.S. 
analog) cellular system is set forth in the flow chart shown in FIG. 3. 
The call processing program is activated immediately after the 
microprocessor 5 is reset when the cellular telephone 2 is turned on. The 
microprocessor 5, under the control of the call processing program, first 
increases the RF detection threshold level. The microprocessor 5 is 
programmed to periodically check the state of the RF detector 12 to 
determine whether an RF signal is being transmitted from the mobile unit 
2. The microprocessor 5 then counts how many times the call processing 
program has detected the presence of an RF signal. If a predetermined 
maximum number of RF signals is detected, then a reliable RF signal is 
present, indicating the cellular telephone 2 is being used for mobile 
cellular telephone service. 
The RF signal transmission from the mobile unit 2 requesting service and 
identifying the mobile unit 2 when power is turned on is known as a 
service request. Once the service request is transmitted from the mobile 
unit 2, the mobile unit 2 turns off its carrier frequency and goes into an 
await message mode, waiting on a reply from the base station 4. The 
cellular monitor then initiates a predetermined delay period referred to 
as a call establishment delay, which extends for the maximum time it might 
take the cellular base station to respond by assigning the initial 
frequencies to be used for signal transmission and reception, plus the 
time it takes for approximately four ringing tones to be emitted from the 
mobile unit 2. The time delay associated with the four ringing tones 
allows the mobile user time to hang up the phone before registering any 
time with the monitoring device 1. Beyond four rings, air time is 
typically charged to the cellular customer. 
At the expiration of the call establishment delay, the microprocessor 5 
lowers the RF detection threshold level. If the user hangs up prior to the 
expiration of the call establishment delay, then the RF signal is no 
longer detected by the RF detection circuit 12, and the call processing 
program activates a hang-up delay period which will be discussed below in 
greater detail. If the call goes through, the RF signal having a magnitude 
greater than or equal to the threshold level is detected by the RF 
detector 12 after the expiration of the call establishment delay such that 
the beginning of a call is established, and the monitoring device 1 begins 
tracking the time associated with the call by activating the time tracking 
program. 
If the RF detector 12 fails to detect the presence of RF signal 
transmission after the expiration of the call delay or after a call is 
established, the microprocessor activates a hang-up delay period. The 
hang-up delay corresponds to a predetermined time interval that prevents 
premature termination of the time tracking functions associated with the 
microprocessor 5 by allowing for potential noise hits which may cause 
momentary losses of RF detection. If RF signal transmission is detected 
after the expiration of the hang-up delay, the microprocessor 5 continues 
monitoring the duration and timing of signal transmissions pursuant to the 
time tracking functions. If RF signal transmissions are not detected after 
the expiration of the hang-up delay period, the call ends and service is 
terminated to the mobile unit 2. The RF detection threshold level is then 
raised, and call processing begins again. 
The cellular monitoring device 1, under the control of the time tracking 
program, constantly displays a function code and associated statistical 
information on the digital display 9. FIG. 4 sets forth a possible list of 
function codes, the format of the statistical information, and function 
descriptions used for a particular billing plan. Each function code is an 
alphanumeric character or set of characters that represent a time tracking 
function performed by the microprocessor 5 under control of the time 
tracking program. For example, function code "5" can be used to indicate 
the current time of day (see FIG. 4), or the phrase "TIME OF DAY" may be 
displayed as the function code. As mentioned above, the time tracking 
functions performed by the microprocessor 5 monitor the duration and 
timing of cellular telephone usage, and generate statistical information 
indicative of the usage of the cellular telephone 2. The function switch 
10 allows the user to selectively display one of a plurality of function 
codes stored in the microprocessor 5, and the current parameter value of 
the statistical information associated with the displayed function code on 
the display 9. As mentioned above, when the user presses or actuates the 
function switch 10, the function code and statistical information 
displayed on the display 9 advances a different function code and 
associated statistical information maintained by the microprocessor 5. 
Function code "P" or "o" is automatically displayed on the display 9 if the 
user has not actuated the function switch 10 or the parameter value switch 
11 for a certain period of time. The "P" function code and associated 
statistical information is automatically displayed if the current time of 
day is within the designated peak period. Likewise, the "o" function code 
and associated statistical information is automatically displayed if the 
current time of day is outside the designated peak period (i.e., the 
off-peak period). 
The time tracking function associated with the "P" function code calculates 
the current peak time used, or if a non-zero value was entered for the 
statistical information corresponding to function code 16 (Set/display 
free peak hours/minutes), the microprocessor 5 calculates the number of 
remaining free minutes. If all remaining free minutes have been consumed, 
and a non-zero value was entered for the statistical information 
corresponding to function code 13 (peak rate, cost per minute) then the 
microprocessor 5 is programmed to calculate total cost. If all remaining 
free minutes have been consumed, and a zero value was entered for the 
statistical information corresponding to function code 13 (peak rate, cost 
per minute) then the microprocessor 5 continues to calculate time, but the 
microprocessor 5 counts up instead of down, and flashes a visual alarm 
and/or sounds an audible alarm (referred to collectively as alarm 20). The 
display 9 shows the current parameter value for the associated statistical 
information when the "P" function code is displayed. 
The microprocessor function associated with the "o" function code operates 
in a manner similar to the "P" function. The "o" function calculates the 
current off-peak time used, or if a non-zero value was entered for the 
statistical information associated with function code 17 (Set/display 
off-free peak hours/minutes), calculates the number of remaining free 
minutes. If all remaining free minutes have been consumed, and a non-zero 
value was entered for the statistical information associated with function 
code 14 (off-peak rate, cost per minute) then the microprocessor 5 
calculates total cost. If all remaining free minutes have been consumed, 
and a zero value was entered for function 14 (off-peak rate, cost per 
minute) then the microprocessor 5 continues to calculate time, but counts 
up instead of down, and flashes the visual alarm and/or sounds the audible 
alarm 20. The display 9 shows the current parameter value for the 
statistical information calculated by the microprocessor 5 when the "o" 
function code is displayed. 
The time tracking function associated with function code 1 calculates the 
current month's total cost to date, which includes peak, off-peak and 
connect charges. When function code 1 is displayed, the display 9 shows 
statistical information indicating the current month's total cost. If no 
rates were entered for peak, off-peak or connect time, then zero is 
displayed for the parameter value. 
When function code 2 is displayed, the display 9 shows statistical 
information indicating the estimated total cost (bill) for the entire 
billing period based upon the rate of telephone usage to date. 
When function code 3 is displayed, the display 9 shows statistical 
information indicating last month's total peak time used. 
When function code 4 is displayed, the display 9 shows statistical 
information indicating last months off-peak time used. 
When function code 5 is displayed, the display 9 shows statistical 
information indicating last months total cost, which includes peak, 
off-peak and connect charges. If no rates were entered for peak, off-peak 
or connect time, then zero is displayed. 
When function code 6 is displayed, the display 9 shows statistical 
information indicating the current time of day. The user can actuate the 
parameter value switch 11 to change the current time of day, if desired. 
When function code 7 is displayed, the display 9 shows statistical 
information indicating the current month and day of month. The user can 
actuate the parameter value switch 11 to change the current month and day, 
if desired. 
When function code 8 is displayed, the display 9 shows statistical 
information indicating the current day of week (MO, TU, WE, TH, Fr, SA, 
SU) along with a numeric code (1 . . . 7) indicating the day of the week 
for the purpose of being foreign language compatible. The user can press 
the parameter value switch 11 to change the current day of the week and 
numeric code, if desired. 
When function code 9 is displayed, the display 9 shows statistical 
information indicating the current year. This is used for determining leap 
years. The user can press the parameter value switch 11 to change the 
current year, if desired. 
When function code 10 is displayed, the display 9 shows statistical 
information indicating the peak start day (MO, TU, WE, TH, Fr, SA, SU) 
along with a numeric code (1 . . . 7) indicating the day of the week. The 
user can actuate the parameter value switch 11 to change the peak start 
day, if desired. 
When function 11 is displayed, the display 9 shows statistical information 
indicating the peak end day (MO, TU, WE, TH, Fr, SA, SU) along with a 
numeric code (1 . . . 7) indicating the day of the week. The user can 
press the parameter value switch 11 to change the peak end day, if 
desired. 
When function code 12 is displayed, the display 9 shows statistical 
information indicating the peak start time of day. The user can actuate 
the parameter value switch 11 to change the peak start time, if desired. 
When function code 13 is displayed, the display 9 shows statistical 
information indicating the peak end time of day. The user can actuate the 
parameter value switch 11 to change the peak end time, if desired. 
When function code 14 is displayed, the display 9 shows statistical 
information indicating the peak rate in dollars and cents (or the 
corresponding local currency) per minute. The user can press the parameter 
value switch 11 to change the peak rate, if desired. 
When function code 15 is displayed, the display 9 shows statistical 
information indicating the off-peak rate in dollars and cents (or the 
corresponding local currency) per minute. The user can press the parameter 
value switch 11 to change the off-peak rate, if desired. 
When function code 16 is displayed, the display 9 shows statistical 
information indicating the connect time rate in dollars and cents (or the 
corresponding local currency) per minute. The user can actuate the 
parameter value switch 11 to change the connect time rate, if desired. 
When function code 17 is displayed, the display 9 shows statistical 
information indicating the number of free peak hours/minutes. The user can 
press the parameter value switch 11 to change the number of free peak 
hours/minutes, if desired. 
When function code 18 is displayed, the display 9 shows statistical 
information indicating the free off-peak hours/minutes. The user can press 
the parameter value switch 11 to change the number of free off-peak 
hours/minutes, if desired. 
When function code 19 is displayed, the display 9 shows statistical 
information indicating the starting day of the month for the user's 
billing period. The user can press the parameter value switch 11 to change 
the starting day of the billing period, if desired. 
When function code 20 is displayed, the display 9 shows statistical 
information indicating the type of cellular telephone system employed. As 
mentioned in the BACKGROUND OF THE INVENTION section, cellular telephone 
systems operate within various ranges of radio frequencies and power 
levels. This feature allows the monitoring device 1 to be used with any of 
the more than one dozen cellular telephone systems in use worldwide, such 
as AMPS, TACS, and NMT-450. The user can press the parameter value switch 
11 to change the cellular system type, if desired. 
The microprocessor function associated with function code 21 allows the 
user to set a lock-out code which locks out or prevents any changes to any 
parameters, until the same lock-out code is re-entered by the user. When 
function code 20 is displayed, the user has the option of changing the 
lock out code by pressing the parameter value switch 11. 
FIG. 5 shows the preferred embodiment of the small, wireless, battery 
operated monitoring device 1 which can be quickly and easily mounted to 
the mobile unit 2 by the user. The overall dimensions of the monitor 1 in 
the preferred embodiment are approximately 1.3".times.0.8".times.0.4". The 
compact design of the monitor 1 allows the monitor 1 to fit unobtrusively 
on the cellular phone 2 near the telephone antenna 3. The monitoring 
device can be used with any manufacturer's cellular telephone, and works 
with any cellular telephone system standards in the United States or 
abroad. The monitor 1 can be attached to the mobile unit 2 in numerous 
fashions. For example, the monitor 1 can be attached to the mobile unit 2 
with a hook and eye type fastener, double-sided sticky foam tape, tamper 
resistant fixtures or tamper indicators (for use with rental cellular 
telephones). The user can reference a slide-out card 18 (shown partially 
in phantom in FIG. 5) which lists the function codes and their 
corresponding function descriptions. A recessed rectangular area 19 allows 
for insertion of a logo or advertisement below the display 9. The 
monitoring device 1 can be employed in conjunction with both analog and 
digital mobile cellular telephone systems, and is programmable by the user 
to switch between the various system types (function code 19). 
FIG. 5 also depicts the visual alarm 20 such as an LED light source which 
alerts the user when no time is available free of charge during peak 
and/or off-peak billing hours. Alternatively, the visual alarm can be 
incorporated into the display 9 such that an indicator appears on the 
display when the free time has been consumed. Similarly, the monitoring 
device can be configured so that the displayed function code and 
statistical information blink rapidly to provide a visual indication to 
the user in this situation. As mentioned above, an audible alarm can be 
provided in addition to or instead of the visual alarm. The audible alarm 
is driven by the microprocessor 5, and provides an audible warning to the 
user when no time is available free of charge during peak and/or off peak 
billing hours. 
In an alternate embodiment of our present invention, the monitoring device 
1 and associated microprocessor functions are incorporated directly into 
the mobile unit 2, thus eliminating the need for antenna 13, RF detection 
circuit 12, comparator 14, and D/A converter 17. In this situation, the 
microprocessor 5 is disposed within the housing of the cellular telephone, 
and is preferably representative of the controller or microprocessor 
typically associated with internal circuitry of the mobile unit. The 
microprocessor uses the standard detection circuitry associated with the 
mobile unit to determine when a signal is transmitted from the cellular 
telephone antenna. The controller or microprocessor of the mobile unit is 
programmed to perform the call processing functions and time tracking 
functions set forth above. Manually operable push button keys 21 
associated with a key pad 22 of the cellular telephone can be used instead 
of push button switches 10 and 11 such that the controller or 
microprocessor is responsive to manual actuation of certain preselected 
keys 21. A digital display that is visible to the user such as the display 
9 discussed above is used to provide a readout of the function codes and 
statistical information. In this situation, the display 16 can be a 
display 23 currently used on cellular telephones to display the number 
dialed. Furthermore, the power source can be a standard rechargeable 
battery typically associated with cellular telephones, such as a Ni--Cd 
battery. However, this alternate embodiment of our present invention may 
not be as desirable to mobile cellular telephone service providers as our 
wireless embodiment because of the problems associated with programming 
changes for the controller or microprocessor if the provider changes the 
billing plan. 
The foregoing description is set forth for illustrative purposes only and 
is not meant to be limiting. Numerous variations, within the scope of the 
appended claims will be apparent to those skilled in the art in light of 
the foregoing description and accompanying drawings. For example, the 
monitoring device 1 can be used in conjunction with a remote antenna and 
RF detection circuit placed in close proximity to the remote antenna, such 
as may be the case with a window mounted antenna. In addition, the 
microprocessor 5 can be replaced with a random logic design. An audible 
alarm can be incorporated into the monitoring device to indicate when all 
free minutes have been consumed. A visual or audible alarm can also be 
provided for alerting the user when the cell battery needs to be replaced. 
The preferred embodiment monitors calls made during peak and off-peak 
hours since standard billing packages associated with mobile cellular 
phone service typically structure a customer's billing plan based on these 
usage patterns. However, the microprocessor 5 clearly can be programmed to 
accommodate alternative billing plans. For example, the monitoring device 
can track the time and cost associated with a billing plan having four 
billing rates corresponding to four periods of time for each day or week. 
Similarly, the monitoring device can monitor only total usage each day if 
a customer's billing plan does not make any distinctions between peak and 
off-peak hours.