In many contexts, particularly in Electromagnetic Compatibility (EMC), a common-mode Current Probe (CP) is intended to be a non-invasive transducer. We introduce its applications generally, but focus on transient waveform measurements. The complex form of our 10 Hz to 1 GHz CP Transfer Impedance (Zt) is measured using Vector Network Analysers. Measured data are compared to manufacturer calibration data and a choice made on the best form of the complex Zt for transient analysis. We then inject a time waveform into a test system and use the Zt to reconstruct the signal, using the inverse Fast Fourier Transform algorithm. The reconstructed current waveform is compared to a reference observation for validation. For frequencies between DC and 240 MHz, a good correlation can be achieved. We raise relevant discussions on filtering, calibration system resonance and de-embedding.