Acoustic emission has been demonstrated as a cost-effective, non-destructive testing technique that can detect and monitor transition elastic waves produced under the stress of material deformation. It is generally deployed in structural testing, process monitoring and materials characterisation. This technique has been applied to the detection of bubble formation in PEMWE by monitoring and analyzing sound waves generated when bubbles form and burst. However, its use and technical capabilities in 'bubble-free' or 'bubble-scarce' electrolysers have not been studied.