Electrical rail mount device (10, 120) for mounting on a rail, comprising - at least one input terminal (51, 52, 53, 121) configured to receive an input line, - fixing means (61, 62, 63, 122) configured to fix the input line to the input terminal (51, 52, 53, 121) to establish an electrical connection, - a lockable cover (20, 125) reversibly movable from an open state into a closed state, whereas the cover is configured to cover the fixing means (61, 62, 63, 122) in the closed state, such that the fixing means can only be accessed by moving the cover from the closed state into the open state, - an electrical element (40, 41, 42, 43, 44, 45, 126) arranged in the cover and configured to provide an electrical function to an active electronic element of the electrical rail mount device (10, 120), wherein an electrical connection is provided between the electrical element (40, 41, 42, 43, 44, 45, 126) and the active electronic element, wherein the electrical rail mount device (10, 120) comprises an electricity meter for measuring power consumption, and wherein - the at least one input terminal (51, 52, 53, 121) is provided as a power terminal (51, 52, 53) configured to receive a power line, and the fixing means (61, 62, 63, 122) is configured to fix the power line to the power terminal (51, 52, 53) to establish an electrical connection, and wherein the electrical element (40, 41, 42, 43, 44, 45, 126) is provided as an auxiliary port (40, 41, 42, 43, 44, 45) configured to receive an auxiliary line, whereas the auxiliary port (40, 41, 42, 43, 44, 45) is configured to allow a communication of an external source with a smart meter gateway comprised by the electricity meter via the auxiliary line, the cover further comprising auxiliary fixing means (30, 31, 32, 33, 34, 35) for fixing the auxiliary line to the auxiliary port (40, 41, 42, 43, 44, 45) positioned such that they are accessible in the closed state of the cover, wherein the cover has a box-like shape, wherein the electrical active parts of the at least one auxiliary port (40, 41, 42, 43, 44, 45) are arranged inside a volume defined by the box-like shaped cover. - at least one input terminal (51, 52, 53, 121) configured to receive an input line, - fixing means (61, 62, 63, 122) configured to fix the input line to the input terminal (51, 52, 53, 121) to establish an electrical connection, - a lockable cover (20, 125) reversibly movable from an open state into a closed state, whereas the cover is configured to cover the fixing means (61, 62, 63, 122) in the closed state, such that the fixing means can only be accessed by moving the cover from the closed state into the open state, - an electrical element (40, 41, 42, 43, 44, 45, 126) arranged in the cover and configured to provide an electrical function to an active electronic element of the electrical rail mount device (10, 120), wherein an electrical connection is provided between the electrical element (40, 41, 42, 43, 44, 45, 126) and the active electronic element, wherein the electrical rail mount device (10, 120) comprises an electricity meter for measuring power consumption, and wherein - the at least one input terminal (51, 52, 53, 121) is provided as a power terminal (51, 52, 53) configured to receive a power line, and the fixing means (61, 62, 63, 122) is configured to fix the power line to the power terminal (51, 52, 53) to establish an electrical connection, and