Over the past decades, sleep-related erection and rigidity monitoring has been used to differentiate psychogenic from organic erectile dysfunction (ED), due to the involuntary nature of erections in sleep. This study retrospectively reviewed all available literature focusing on sleep-related erection and rigidity monitoring through a systematic PubMed search. To date, there are mainly seven methods and their modifications, including: sleep laboratory testing, the mercury strain gauge, the stamp test, the erectometer, the Snap gauge, the RigiScan, and nocturnal electrobioimpedance volumetric assessment. This study analyzes and summarizes the advantages and limitations of seven monitoring methods. This study indicates that both of the above methods possess the capacity to assess erectile quality and provide guidance to the diagnosis, etiology, and differential diagnosis of ED. However, some limitations still exist for the application. New devices which can continuously monitor kinds of variables, including sleep-related erection, axial and radial rigidity, and oxygen saturation are needed.