Durability and performance of electrochemical energy converters such as fuel cells and electrolysers are not only dependent on the properties and the quality of the used materials. They strongly depend on operation conditions. Variations in external parameters, such as flow, pressure, temperature and, obviously, load can lead to significant local changes of current density, even local transients. The segmented cell technology was developed with the purpose to gain insight into local operation conditions in electrochemical cells, during operation. The operando measurement of the local current density and temperature distribution allows effective improvement of operation conditions, mitigation of potentially critical events and assessment of the performance of new materials. The segmented cell, which can replace a regular bipolar plate in the current state of the technology, can be used as monitoring tool and for targeted developments. This article gives an overview over the development and applications for proton exchange membrane fuel cell of this technology, such as water management or fault recognition. Recent advancements towards locally resolved monitoring of humidity and to current distributions in electrolysers are outlined.