System and method are provided for continually monitoring reliability, or aging, of a digital system and for issuing a warning signal if digital system operation degrades past a specified threshold. The technique includes implementing a ring oscillator sensor in association with the digital system, wherein logic and/or device percent composition of the ring oscillator sensor mirrors percent composition thereof within the digital system. Counter logic is coupled to the ring oscillator sensor for converting outputted count signals to an oscillation frequency, and control logic is coupled to the counter logic for periodically evaluating oscillation frequency of the ring oscillator sensor and generating a warning signal indicative of reliability degradation if at least one of: (i) a measured or estimated oscillation frequency is below a warning threshold frequency; or (ii) a measured or estimated rate of change in a difference between measured oscillation frequencies exceeds an acceptable rate of change threshold.