A cable failure device for a cable-operated door operated by a tensioned cable, the cable-operated door having a movement guided along a fixed structure, such as a guide rail. The cable failure device is configured for cooperating with the tensioned cable so as to immobilize the cable-operated door with respect to the fixed structure in the event of a loss of tension in the cable. The cable failure device included a support bracket for mounting the cable failure device onto the door, a guiding assembly operatively mounted for guiding the movement of the door along the fixed structure, and a braking assembly operatively mounted onto the support bracket, and operable between a rest position where the guiding assembly is allowed to guide the door along the fixed structure, and an operable position triggered by a given loss of tension detected in the tension cable where the braking assembly engages a portion of the fixed structure for braking movement of the cable-operated door with respect to the fixed structure. The cable failure device also includes a safety arm operatively connected to the braking assembly and cooperating with the tensioned cable so as to detect the given loss of tension. The safety arm is operable between a safety configuration where it is positioned over at least one fastener of a corresponding hole of the support bracket when there is still a given tension in the tensioned cable, for preventing a user from removing the support bracket from the door, and a retracted configuration where the safety arm is positioned away from the fastener when the given tension is no longer present in the cable, thereby enabling the user access to the fastener. Thus, the cable failure device is configured for immobilizing the door in the event of a loss of tension and for preventing a user from removing the device from the door when there is still tension in the cable.