The present invention relates to a method and radiation monitoring device (10) comprising at least one radiation detector (111), a memory (112) and a controller (12), wherein said radiation detector is arranged to detect at least one type of radiation dose. The memory (112) comprises a number of memory positions configured to store data resulting from said detector (111) detection. The positions are configured to store accumulated measured dose values corresponding to consecutive real time intervals. The controller is configured to continuously compute mean radiation dose values for measured and stored radiation doses during the predetermined time period and for each computation, a resulting mean value is compared with a corresponding predetermined reference value and generate a signal corresponding to result of said comparison.