Testing and debugging of immunity issues is challenging in part because it is not known which components inside a system are impacted by an immunity test or at what level. Attaching cables and probes to determine stress voltages and currents within a system is time consuming and can alter the test results. Sensors are proposed for measuring the peak stress voltage experienced within a system during a transient immunity test. The peak current can also be found when the sensor is placed across a transient voltage suppressor with a known I-V curve. The peak level is transmitted wirelessly to a receiver outside the system using frequency-modulated magnetic or electric fields, thus allowing multiple measurements to be made without opening the enclosure or otherwise modifying the system. Two sensing circuits are proposed: one that stores the peak voltage on an external capacitor and the other that uses an analog-to-digital converter to store the level in a register. The capabilities of the circuits were validated with a combination of SPICE and electromagnetic simulations when the sensor was placed inside a typical cell phone enclosure. Simulations demonstrate that the sensors can accurately detect the peak transient voltage and transmit the level to an external receiver.