The invention provides a fault alarm device which is suitable for the field of power distribution. The device comprises a low-voltage direct-current fault alarm circuit; the low-voltage direct-current fault alarm circuit comprises a relay for controlling alarm and an aircraft plug with one end connected with the relay; and a normally open switch controlled by the relay connected in series in a low-voltage direct-current protective circuit is arranged between two end points of the aircraft plug. The device further comprises an isolating corresponding switch connected in series in the low-voltage direct-current fault alarm circuit. In the embodiment of the invention, through adding the isolating corresponding switch in the low-voltage direct-current fault alarm circuit, when a power circuit breaker is required to be isolated, the isolating corresponding switch is unloosened, so as to enable the low-voltage direct-current fault alarm circuit to be broken, thereby avoiding damage to a screw socket and a pinhead caused by repeated insertion of the aircraft plug, as well as switch misoperation or malfunction caused by the poor contact of the plug. Furthermore, the invention does not need to change an original design function, and has the advantages of simple operation, convenient and flexible use and strong applicability.