We consider the concept of active diagnostics for detecting and registering hardware faults in computers, sensors, executive mechanisms, and optical electronic systems. We propose a collection of informative features to detect and register sources of the faults: connectors, contacting units of large integral circuits (LIC) and super-large integral circuits (SLIC), contacting conductors on printed circuit boards (including multilayered ones), interface buses, unshielded single- and multicore wires, grounding and power buses, connector blocks, brazing joints. Based on these new properties of passive elements in radioelectronic hardware, and in keeping with the notion of "fail-safeness," we propose a new notion of reliability, "fault-safeness," that establishes a connection between hardware faults and its hidden defects.