An anti-theft system for motor vehicles. A receiver reference signal is generated by combining the calibrating output signal of the transmitter and a signal whose carrier signal has a frequency equaling the frequency of the local oscillator signals, conducting the combined signal through a band-pass filter and amplifying it. In one example, when the host computer is not coupled with the upstream port, the local host communicates with the peripherals; and when the host computer is coupled with the upstream port, the local host disconnects from the upstream port so that the host computer communicates with the peripherals through the hub. The method also includes adjusting the pH of the wastewater to reduce the chemical oxygen demand of the wastewater.