The auxiliary control system contains at least a first interaction device and a second interaction device that are capable of mutually detecting the presence of each other by a wireless means. The first interaction device is carried by a driver of a motor vehicle having a built-in anti-theft system, and the second interaction device is tapped into a Main Body ECU in parallel with the original control interface of the built-in anti-theft system. As such, when the driver carrying the first interaction device enters into or moves out of an effective sensing range from the motor vehicle, the second interaction device would detect the presence or absence of the first interaction device. The second interaction device then issues appropriate deactivating or activating signals to the Main Body ECU which in turn disarms or arms the various anti-theft means of the motor vehicle.