Mobile telephone device system having steal prevention function

In a mobile telephone device having a preassigned call number and comprising a power supply unit, a keyboard section, a display section, a power key, and a control section, the mobile telephone device transmits, on position registration operation, a position registration signal including the preassigned call number to the base station and receives an information signal from the base station as a result of the position registration operation. The information signal is for representing whether or not the preassigned call number coincides with that of a stolen mobile telephone device. The control section invalidates the operation of the keyboard and the power key and stops display of the display section and then transmitting an alarm signal to the base station on reception of the information signal representing the fact that the preassigned call number coincides with that of the stolen mobile telephone device.

BACKGROUND OF THE INVENTION 
This invention relates to a mobile telephone device having steal prevention 
function. Such a mobile telephone device is particularly useful in a 
portable radio telephone device. 
An example of the mobile telephone device is disclosed in Japanese Patent 
Publication No. Tokkosho 63-65250 (65250/1988). The mobile telephone 
device is used in a steal prevention system. The steal prevention system 
is for the mobile telephone device which is used on an automobile and aims 
to carry out a follow-up survey when the automobile having the mobile 
telephone device was stolen. Namely, the steal prevention system is for 
establishing the follow-up survey of a stolen automobile even if the 
mobile telephone device loaded on the stolen automobile is not used. The 
steal prevention system is based on the fact that the mobile telephone 
device has a preassigned call number. In the following description, the 
mobile telephone device loaded on the stolen automobile is called a stolen 
mobile telephone device. 
In order to establish the above-mentioned purpose, the steal prevention 
system comprises a base station for connecting the mobile telephone device 
to a telephone network. The steal prevention system is on the premise that 
a call number of the stolen mobile telephone device is registered, as a 
stolen call number, in the base station. For the reason, the base station 
comprises a memory unit memorizing the stolen call number. The base 
station transmits an information signal including the stolen call number. 
On the other hand, the mobile telephone device receives the information 
signal even if the mobile telephone device is not used, namely, even if a 
power switch is put into an off state. The mobile telephone device 
comprises a power supply unit which is removably attached to a body of the 
mobile telephone device and a decision section for carrying out a decision 
operation whether or not the preassigned call number coincides with the 
stolen call number included in the information signal. When the decision 
section decides that the preassigned call number coincides with the stolen 
call number, a transmitting section is activated and transmits an alarm 
signal representative of a fact that the preassigned call number coincides 
with the stolen call number. 
When the alarm signal is received by the base station, the alarm signal is 
displayed by a display unit in the base station. Then, the base station 
carries out the follow-up survey of the stolen automobile by the use of 
the alarm signal. 
As mentioned above, since the mobile telephone device always monitors the 
information signal, the mobile telephone device has an increased power 
consumption. This means that the increased power consumption hastens 
voltage drop of the power supply unit. 
Furthermore, if the power supply unit is removed from the body of the 
mobile telephone device, it is impossible to monitor the information 
signal and to transmit the alarm signal. This means that it is impossible 
to establish the above-mentioned purpose. The above-mentioned operation is 
applied to the mobile telephone device which is not loaded on the 
automobile. 
SUMMARY OF THE INVENTION 
It is therefore an object of this invention to provide a mobile telephone 
device which is capable of improving a battery saving efficiency and which 
is capable of improving steal prevention function. 
It is another object of this invention to provide the mobile telephone 
device which is capable of establishing a follow-up survey of a stolen 
mobile telephone device, even if a power supply unit is removed from the 
stolen mobile telephone device. 
It is a further object of this invention to provide a steal prevention 
system which is suitable for the above-mentioned mobile telephone device. 
According to an aspect of this invention, a mobile telephone device has a 
preassigned call number and comprises a power supply unit for supplying 
electric power through a power supply line and removably attached to a 
body of the mobile telephone device. The mobile telephone device further 
comprises a keyboard section, a display section, a power key for 
instructing power supply from the power supply unit, and a control section 
connected to the keyboard section, the display section, and the power key 
for controlling operation of the keyboard section, the display section, 
and the power key. The mobile telephone device transmitting, on position 
registration operation for registering the preassigned call number to the 
base station, a position registration signal including the preassigned 
call number to the base station and receiving an information signal from 
the base station as a result of the position registration operation. The 
information signal is for representing whether or not the preassigned call 
number coincides with that of a stolen mobile telephone device. The 
control section invalidates the operation of the keyboard and the power 
key and stopping display of the display section and then transmitting an 
alarm signal to the base station on reception of the information signal 
representing the fact that the preassigned call number coincides with that 
of the stolen mobile telephone device.

DESCRIPTION THE PREFERRED EMBODIMENT 
Referring to FIG. 1, description will be made with regard to a mobile 
telephone device according to a preferred embodiment of this invention. 
The mobile telephone device has a preassigned call number and comprises a 
main battery 1, a keyboard section 2, a display section 3, a power key 4, 
a radio section 5, a control section 6, and an antenna 7. 
The main battery 1 is for supplying electric power through a power supply 
line L1. As well known in the art, the main battery 1 is removable from a 
body of the mobile telephone device and is chargeable by a battery 
charger. Such a main battery 1 may be called a power supply unit or an 
outer battery. The power key 4 is for instructing power supply from the 
main battery 1. In other words, when the power key 4 is pushed, the power 
supply is started from the main battery 1. As will later become clear, the 
radio section 5 is for receiving a radio signal, such as an information 
signal and a control signal, from a base station 20 and transmitting a 
transmission signal, such as a position registration signal and an alarm 
signal, to the base station 20. Although the radio section 5 receives and 
transmits various other signals in telephone talk, the description for the 
other signals is omitted. Needless to say, the base station 20 is for 
connecting the mobile telephone device to a telephone network(not shown). 
The control section 6 is for carrying out control operation of a reception 
operation and a transmission operation both of which are required to carry 
out the telephone talk. Since the control operation for the telephone call 
is well known in the art, the description of the control operation is 
omitted. In addition to the above-mentioned control operation, the control 
section 6 controls operation of the keyboard section 2, the display 
section 3, and the power key 4 as will later be described. 
The mobile telephone device further comprises an auxiliary battery 10, an 
overcurrent protection circuit 11 connected between the main battery 1 and 
the auxiliary battery 10, a first diode D1 inserted into the power supply 
line L1, a second diode D2 connected between the first diode D1 and the 
overcurrent protection circuit 11, and a switch section 12 connected in 
parallel to the second diode D2 and the overcurrent protection circuit 11 
and to the control section 6. 
While the switch section 12 is put into an off state, the auxiliary battery 
10 is charged from the main battery 1. Under the circumstances, a supply 
line connected between the main battery 1 and the auxiliary battery 10 
serves as a charging circuit. While a charge operation is carried out, the 
auxiliary battery 10 is protected by the overcurrent protection circuit 11 
from the overcurrent. The first diode D1 is for preventing the current 
which flows from the auxiliary battery 10 to the main battery 1. The 
second diode D2 is for preventing the current which flows to the power 
supply line L1 when the switch section 12 is put into the off state. In 
other words, the auxiliary battery 10 can supply the electric power 
through the power supply line L1 only when the switch section 12 is put 
into an on state. As will later be described, the switch section 12 is put 
into the on state in first and second cases under control of the control 
section 6. It should be noted here that the auxiliary battery 10 is 
included into the body of the mobile telephone device and is therefore 
hard to remove from the body. Under the circumstances, the auxiliary 
battery 10 may be called an inner battery. 
Although it is not illustrated in FIG. 1, the mobile telephone device 
further comprises a remaining quantity display unit for displaying 
remaining quantity of electric power in the main battery 1. A user decides 
whether or not the remaining quantity of the electric power is sufficient 
for driving the mobile telephone device by monitoring the remaining 
quantity display unit. If the user decides that the remaining quantity of 
the electric power is insufficient, the user puts a predetermined key in 
the keyboard section 2. When the predetermined key is put, the control 
section 6 puts the switch section 12 into the on state. As a result, the 
electric power is supplied from the auxiliary battery 10 through the 
switch section 12 in addition to the main battery 1. This case is 
applicable to the first case mentioned before. 
Referring to FIGS. 2 and 3 together with FIG. 1, the description will be 
made as regards steal prevention operation for steal prevention of the 
mobile telephone device. Strictly, the word of "steal prevention" to which 
the present invention aims means preventing to use a stolen mobile 
telephone device. If the mobile telephone device is stolen, the user 
registers the preassigned call number of the stolen mobile telephone 
device as a stolen call number. In order to realize the steal prevention, 
the base station 20 comprises a memory unit 21 (FIG. 3) for memorizing the 
stolen call number as a particular call number. When the stolen call 
number is registered in the base station 20, it is stored in the memory 
unit 21 in the base station 20. In FIG. 3, the mobile telephone device 
illustrated in FIG. 1 is symbolically depicted at 30. 
The steal prevention operation is carried out together with position 
registration operation which is known in the art. The position 
registration operation is started when the power key 4 is pushed. At a 
first step S1, the control section 6 starts signal monitoring operation 
for measuring an electric field level of a reception signal received by 
the radio section 5. Such a signal monitoring operation is called channel 
scanning operation. Namely, the signal monitoring operation is carried out 
in order to search a particular channel which has a highest electric field 
level. 
At a second step S2, the particular channel is decided based on the result 
of the signal monitoring operation. At third step S3, the position 
registration signal comprising the preassigned call number is transmitted 
by the particular channel under control of the control section 6. The 
position registration signal is received by the base station 20 that has 
the particular channel. At a fourth step S4, the base station 20 transmits 
the control signal which designates a control channel required for the 
telephone talk. 
The base station 20 further comprises a decision unit 22 for deciding 
whether or not the preassigned call number coincides with the stolen call 
number memorized in the memory unit 21. At a fifth step S5, the base 
station 20 transmits the information signal which represents whether or 
not the preassigned call number is that of the stolen mobile telephone 
device. Namely, if the preassigned call number coincides with the stolen 
call number, the information signal represents the fact that the 
preassigned call number coincides with the stolen call number. This means 
that the mobile telephone device 30 is the stolen mobile telephone device. 
When the preassigned call number does not coincide with the stolen call 
number, the information signal represents that the preassigned call number 
does not coincide with the stolen call number. This means that the mobile 
telephone device 30 is not the stolen mobile telephone device. 
At a sixth step S6, the mobile telephone device 30 receives the information 
signal. The control section 6 decides whether or not the information 
signal represents that the preassigned call number coincides with the 
stolen call number. If the information signal represents that the 
preassigned call number does not coincide with the stolen call number, the 
operation proceeds to a seventh step S7. At the seventh step S7, the 
control section 6 shifts to a stand-by mode. In the stand-by mode, the 
control section 6 monitors the control channel in order to prepare for 
calling. 
If the information signal represents that the preassigned call number 
coincides with the stolen call number, the sixth step S6 Is succeeded by 
an eighth step S8. At the eighth step S8, the control section 6 
invalidates operation of the power key 4. In other words, the control 
section 6 disregards the push operation of the power key 4. 
Simultaneously, the control section 6 invalidates the operation of the 
keyboard 2 and stops display of the display section 3 at a ninth step S9. 
Thus, the mobile telephone device 30 becomes impossible to use. 
Furthermore, the control section 6 puts the switch section 12 into the on 
state when the information signal represents that the preassigned call 
number coincides with the stolen call number. As a result, the auxiliary 
battery 10 supplies the electric power through the switch section 12 and 
the power supply line L1. This case is applicable to the second case 
mentioned in conjunction with FIG. 1. Then, the control section 6 carries 
out transmission of the alarm signal which represents that the mobile 
telephone device 30 is the the stolen mobile telephone device. Moreover, 
the alarm signal represents that the mobile telephone device 30 was set on 
an unserviceable state. The base station 20 receives the alarm signal and 
carries out a follow-up survey by the use the alarm signal. It should be 
noted here that the mobile telephone device 30 continues transmission of 
the alarm signal if the main battery 1 is removed from the body of the 
mobile telephone device 30. This is because the electric power is supplied 
from the auxiliary battery 10. This is the reason why the auxiliary 
battery 10 is included in the body of the mobile telephone device 30. 
The above-mentioned operation is applied to a case that the mobile 
telephone device is used on an automobile. In this case, a battery unit 
mounted on the automobile may be used in place of the main battery 1. 
According to the present invention, it is possible to improve a battery 
saving efficiency because the mobile telephone device 30 monitors the 
information signal only when the mobile telephone device 30 carries out 
the position registration operation. 
While this invention has thus far been described in conjunction with a 
preferred embodiment thereof, it will readily be possible for those 
skilled in the art to put this invention into practice in various other 
manners.