An apparatus and method that intentionally illuminate a number of target devices with RF energy having specific characteristics (e.g., frequency, power, waveform, directionality, duration, etc.) are provided. The target devices, which may comprise a computer system or other electronic circuits, by their fundamental nature as mixed analog and digital devices, act as non-linear mixers and are forced to emit information about the target device behavior, state, and physical characteristics. The apparatus that implements the method receives the forced emissions signals, extracts useful data from noise, and analyzes the data to determine target device characteristics. The target devices may be powered or unpowered. The apparatus and method provided may avoid impacting target device operation.