Creation of subsystems for technical diagnostics and monitoring is a popular way for providing a high level of reliability and safety of supervisory systems. Similar systems are actively developed during the first half of the XXI century: new measuring controllers are being created, with mode of operation based on different physical effects, the degree of automation of the diagnostic information analysis are increasing, and the field of implementation are being expanded. The paper reviews the problems of organization of subsystems for technical diagnostics and monitoring of automation and remote control devices of St. Petersburg subway lines - «Parnas» and «Spasskaya» stations and adjacent spans. The subsystem of technical diagnostics and monitoring was created by modernization of the known system «Hardware and software complex of supervisory control» and is one of the first systems operating at the metro facilities. The article describes the features of upgraded system, the sequence of actions for its design on selected facilities of St. Petersburg subway, as well as the features of automation of the analysis process of diagnostic information by the example of the logical analysis of adjacent track circuits. It also includes the disadvantages of the new system of continuous monitoring of a technical condition, as well as methods to improve it.