A tamper detection circuit, comprising: an active tamper detection circuit for being coupled to an active tamper loop formed over a device to be protected from tampering, during an active tamper detection mode, the active tamper detection circuit detecting when conductivity of the active tamper loop is broken; and a bypass detection circuit comprising: a voltage comparator having a first input terminal for being coupled to a first end of the active tamper loop, a second input terminal for being coupled to the second end of the active tamper loop, an output terminal, and a control terminal; a calibration engine, which includes a variable hysteresis control circuit, configured to sweep a hysteresis voltage applied to the control terminal to generate and store a sweep signature during a boot-up sequence of the bypass detection circuit, wherein the sweep signature is an indication of a voltage at which an output voltage of the voltage comparator transitions from a logic high to a logic low, or vice versa; and the variable hysteresis control circuit having an output terminal coupled to the control terminal of the voltage comparator and configured to periodically sweep the hysteresis voltage at a pre-selected step size to generate an output voltage sweep of the voltage comparator, wherein during a calibration mode of the bypass detection circuit, the output voltage sweep is compared to the stored sweep signature to detect a mismatch between the stored sweep signature and the output voltage sweep being indicative of a tamper. an active tamper detection circuit for being coupled to an active tamper loop formed over a device to be protected from tampering, during an active tamper detection mode, the active tamper detection circuit detecting when conductivity of the active tamper loop is broken; and a bypass detection circuit comprising: a voltage comparator having a first input terminal for being coupled to a first end of the active tamper loop, a second input terminal for being coupled to the second end of the active tamper loop, an output terminal, and a control terminal; a calibration engine, which includes a variable hysteresis control circuit, configured to sweep a hysteresis voltage applied to the control terminal to generate and store a sweep signature during a boot-up sequence of the bypass detection circuit, wherein the sweep signature is an indication of a voltage at which an output voltage of the voltage comparator transitions from a logic high to a logic low, or vice versa; and the variable hysteresis control circuit having an output terminal coupled to the control terminal of the voltage comparator and configured to periodically sweep the hysteresis voltage at a pre-selected step size to generate an output voltage sweep of the voltage comparator, wherein during a calibration mode of the bypass detection circuit, the output voltage sweep is compared to the stored sweep signature to detect a mismatch between the stored sweep signature and the output voltage sweep being indicative of a tamper. a voltage comparator having a first input terminal for being coupled to a first end of the active tamper loop, a second input terminal for being coupled to the second end of the active tamper loop, an output terminal, and a control terminal; a calibration engine, which includes a variable hysteresis control circuit, configured to sweep a hysteresis voltage applied to the control terminal to generate and store a sweep signature during a boot-up sequence of the bypass detection circuit, wherein the sweep signature is an indication of a voltage at which an output voltage of the voltage comparator transitions from a logic high to a logic low, or vice versa; and the variable hysteresis control circuit having an output terminal coupled to the control terminal of the voltage comparator and configured to periodically sweep the hysteresis voltage at a pre-selected step size to generate an output voltage sweep of the voltage comparator, wherein during a calibration mode of the bypass detection circuit, the output voltage sweep is compared to the stored sweep signature to detect a mismatch between the stored sweep signature and the output voltage sweep being indicative of a tamper.