Abstract: A computerized monitoring system which incorporates the power lines that provide electrical power to the remote devices as the physical communications medium of a serial data bus for the computer system. The system comprises a central computer and a plurality of computerized sensor modules within the individual remote devices. The central computer and each of the sensor modules has associated with it a respective data link for coupling respective signal generating and receiving means to the power distribution lines and for manipulating the signals to and from a form suitable for transmission on the power distribution lines. Phase shift keying is used wherein binary bits of data are represented as 180.degree. phase shifts of the pulses in a carrier pulse train. A data transmission rate of approximately 15,000 baud with a carrier frequency of 120 kHz is typical.