A derail placement warning system for a railway derailer that automatically generates an alert to inform railway personnel (or others) of the placement of the derailer on a rail of the railway such that the derailer will derail rail traffic over the derailer. The warning system has an electronic circuit with an electric power source, an electronic switch and an electronic alert, and is configured for the switch to automatically activate and turn ON the alert when the derailing component of the derailer is positioned atop a railway rail. The alert comprises one or more of an audible component, a tactile sensation, an olfactory component, a visible light emission, and an electronic transmission.