A safety device for switching a wind turbine between a safe mode of operation and a normal mode of operation, the safety device comprising a controller (110, 210) comprising a first pair of terminals (111, 112; 211, 212), a second pair of terminals (113, 114; 213, 214), and control logic, the control logic being adapted to generate an output signal indicative of either the safe mode of operation or the normal mode of operation, and a switching assembly (120, 220) operable to select one of the normal mode of operation and the safe mode of operation, the switching assembly comprising a first switch (121, 221) and a second switch (122, 222) adapted to operate synchronously, wherein the first switch is adapted to selectively connect and disconnect the first pair of terminals, and wherein the second switch is adapted to selectively connect and disconnect the second pair of terminals, wherein the control logic is adapted to generate the output signal indicative of the normal mode of operation when both the first pair of terminals and the second pair of terminals are respectively connected, and to generate the output signal indicative of the safe mode of operation when at least one of the first pair of terminals and the second pair of terminals are not respectively connected, wherein the controller further comprises a first signal generator connected to one of the first pair of terminals and adapted to generate a first characteristic signal, the first characteristic signal being a pulsed signal having a first frequency and a first duty cycle, a first signal detector connected to the other one of the first pair of terminals and adapted to detect the first characteristic signal, a second signal generator connected to one of the second pair of terminals and adapted to generate a second characteristic signal, the second characteristic signal being a pulsed signal having a second frequency and a second duty cycle, and a second signal detector connected to the other one of the second pair of terminals and adapted to detect the second characteristic signal, wherein the control logic is adapted to determine that the first pair of terminals are connected when the first signal detector detects the first characteristic signal and determine that the second pair of terminals are connected when the second signal detector detects the second characteristic signal, and wherein the first frequency differs from the second frequency and/or the first duty cycle differs from the second duty cycle. a controller (110, 210) comprising a first pair of terminals (111, 112; 211, 212), a second pair of terminals (113, 114; 213, 214), and control logic, the control logic being adapted to generate an output signal indicative of either the safe mode of operation or the normal mode of operation, and a switching assembly (120, 220) operable to select one of the normal mode of operation and the safe mode of operation, the switching assembly comprising a first switch (121, 221) and a second switch (122, 222) adapted to operate synchronously, wherein the first switch is adapted to selectively connect and disconnect the first pair of terminals, and wherein the second switch is adapted to selectively connect and disconnect the second pair of terminals, wherein the control logic is adapted to generate the output signal indicative of the normal mode of operation when both the first pair of terminals and the second pair of terminals are respectively connected, and to generate the output signal indicative of the safe mode of operation when at least one of the first pair of terminals and the second pair of terminals are not respectively connected, wherein the controller further comprises a first signal generator connected to one of the first pair of terminals and adapted to generate a first characteristic signal, the first characteristic signal being a pulsed signal having a first frequency and a first duty cycle, a first signal detector connected to the other one of the first pair of terminals and adapted to detect the first characteristic signal, a second signal generator connected to one of the second pair of terminals and adapted to generate a second characteristic signal, the second characteristic signal being a pulsed signal having a second frequency and a second duty cycle, and a second signal detector connected to the other one of the second pair of terminals and adapted to detect the second characteristic signal, wherein the control logic is adapted to determine that the first pair of terminals are connected when the first signal detector detects the first characteristic signal and determine that the second pair of terminals are connected when the second signal detector detects the second characteristic signal, and