There are questionnaires and scales, including self-assessment scales, used to evaluate suicide risk. Additionally, suicide risk factors (i.a., prior suicide attempts, willingness to commit suicide, somatic diseases, male gender) are also known. Their application, however, does not provide a sufficient guarantee for properly distinguishing persons with high and low suicide risk. In 1986, Gunnar Edman observed that there is an association between low electrodermal activity and suicidal tendencies, which was confirmed in other studies and meta-analyses. Electrodermal activity (EDA) is commonly considered to be a very good indicator of orienting reflex, which is a response to the information linked with a stimulus and, in a way, a physiological mechanism that helps an organism to survive. This phenomenon is related to habituation, the rate of which is a measure of EDA reactivity. Hyporeactivity consists in very rapid habituation of a stimulus, even after first exposure. According to Lars Håkan Thorell, hyporeactivity may be understood as a specific deficit of attention, which is associated with inability to arouse curiosity with ordinary, everyday events at the physiological level. This results in a greater tendency to attempt suicide shown by persons with mood disorders, and lower fear of hurting oneself. The goal of this paper is to present history of studies on electrodermal activity, relationship between EDA and suicide tendencies in persons with affective disorders and to discuss EDOR System that identifies persons at particularly high risk of committing suicide.