Higgs factories are increasingly identified as high priority by international strategy processes. There is not yet a decision on where to build it, or what technology to pick. A prudent strategy for research in physics and detectors is to emphasize aspects that benefit multiple technologies. However, some of the differences between detectors at linear and circular colliders require dedicated research to meet the physics requirements. In this talk I will point out similarities and differences between detectors at different accelerators and identify areas where new research can significantly improve the physics output.