Security system with automatic door locking/unlocking function

A car security alarm system comprising:

• a transmitter portion to be carried by a car driver, the transmitter portion comprising a signal generation circuit which generates an encoded signal comprising an identification code and a transmitting circuit which automatically and repeatedly emits the encoded signal at predetermined intervals;
• and
• a receiver portion adapted to be incorporated in a car having a door and an electrical system, the receiver portion comprising:
• a receiving circuit for receiving the encoded signal from the transmitter portion;
• an amplifier circuit connected to the receiving circuit for amplifying the signal received by the receiving circuit;
• a decoder circuit connected to the amplifier circuit for decoding the signal received by the receiving circuit and amplified by the amplifier circuit to obtain the identification code carried by the received signal;
• storage means storing therein at least one set of data for confirming the identification code carried by the received signal;
• an identifying circuit which receives the decoded signal from the decoder circuit and accesses the data stored in the storage means to confirm the identification code of the received signal and generates a confirmation signal;
• a central processing unit which receives the confirmation signal from the identification circuit to provide a driving signal and a control signal;
• a driving circuit which is coupled to the car electrical system, the driving circuit receiving the driving signal from the central processing unit to lock/unlock the car door;
• and
• an alarm generation circuit which is coupled to the central processing unit to receive the control signal therefrom for activating/de-activating the alarm generation circuit to generate an alarm signal,
• wherein when the car security alarm system is in an activated condition, the receiver portion, upon receiving the encoded signal from the transmitter portion deactivates the car security alarm system and unlocks the car door, and when the car security alarm system is in de-activated condition, the receiver portion, upon detecting no such encoded signal from the transmitter portion, activates the car security alarm system and locks the car door.