US Patent 7420291 Security apparatus

A security apparatus is installed in a vehicle including a door-lock control device for performing a door lock control on the basis of a signal transmitted from a portable transmitter, which a legitimate driver should take along. The security apparatus prevents a theft of the vehicle. The security apparatus includes a receiving circuit, an antenna, and a control circuit. The receiving circuit can receive the signal transmitted from the portable transmitter. The control circuit has a function of switching a security mode on the basis of a reception state of the receiving circuit and a member relating to the door lock control such as a door lock motor.