A power-on-reset circuit (POR) for integrated circuits that detects the minimum power levels needed to operate the most critical circuit(s) reliably. The circuit is implemented in a customized POR built into a custom IC, and emulates the critical circuit transistors in the custom IC using mimicking counterparts which are similarly affected by changes in temperature and process variations as the main circuit components. The mimicking counterparts may have smaller dimensions, to draw less current but still emulate the characteristics of the main working circuit components. Each critical sub-circuit of the main circuit may have a mimicking POR, and the multiple PORs may have their outputs combined by logic so that subtle failure modes can be modeled in the POR. The POR allows operation of the main circuit to continue at the lowest possible voltage levels while reducing the risk of unexpected results or undetected non-catastrophic failures. The POR also implements safety margins for the operation of the main circuit and tracks process sensitivity.