There is strong motivation to extend the observable frequency range of gravitational waves (GWs) beyond the Hz - kHz regime already probed by LIGO and Virgo. In particular, higher-frequency GWs can give rise to new classes of electromagnetic signals that can be searched for with small-scale detectors. A gauge-invariant description shows that existing experiments designed for the detection of axion dark matter only need to reanalyze existing data to search for such signals. I will also discuss how electromagnetic cavities can operate as exquisite mechanical to electromagnetic converters, enabling a broader search across orders of magnitude of unexplored parameter space.