The parametric shifts or circuit failures caused by transistor aging have become more severe with shrinking device sizes and voltage margins. Designing circuits that can withstand these aging effects is particularly critical in medical applications where systems must operate flawlessly across a range of conditions for their entire lifetimes. In this work we present several on-chip Silicon Odometers that provide measurement data required to develop transistor degradation models. One such scheme - a beat frequency detection circuit capable of recording oscillator frequency shifts ranging down to a theoretical limit of less than 0.01% - may be suited to trigger real-time adjustments that compensate for lost performance on products in the field. Incorporating this sensing capability may be especially attractive in implantable medical electronics.