Detecting voltage-based attacks on an integrated circuit (IC) is difficult in the presence of clock jitter. Propagating signals can exhibit a total delay that is due to a delay component resulting from a voltage-based attack and a delay characteristic resulting from clock fluctuation. Voltage-variation detection circuitry includes first and second voltage-dependent circuits and a voltage analysis circuit. The voltage-dependent circuits produce first and second signals that are indicative of a voltage level responsive to a clock signal and based on different first and second voltage sensitivities. The voltage analysis circuit generates a voltage alert signal based on the first and second signals. A combined signal neutralizes the delay characteristic in the first and second signals, but the delay component due to the voltage variation can be at least partially maintained. Thus, a voltage-based attack is detectable in the presence of clock fluctuation by using two voltage-dependent circuits.