Determining the components or coupling path responsible for soft failures during transient testing is challenging, in part because components are hidden deep within the product and because measuring internal voltages or currents during a transient test may not be practical. Adding cables to the system to make voltage or current measurements may be difficult and may alter the test results. To overcome this problem, a compact sensor has been designed to measure the peak over-or under-voltage on a trace or pin during a transient electromagnetic event. The sensor was designed to wirelessly transmit the peak level of the event to a receiver outside the device under test using frequency-modulated electric and magnetic fields, so that no cabling or other changes to the system are needed. A proof-of-concept of the sensor has been implemented in an integrated circuit (IC) using 180 nm technology which can measure the peak level of a negative transient event. The sensor operation was validated by direct injection to the sensor from a transmission line pulser. The sensor was also used to detect the peak voltage on a USB cable during a transient event on the cable-connected system. Tests showed that the sensor can successfully detect and transmit the peak level of the event, and that the oscillation frequency (and thus the level) could be easily detected by a near-field probe placed outside the enclosure of the device under test.