Abstract: An electronic whistle in the form of broad band radio frequency interference generator. A broad band generator generates a coherent or random noise signal which is modulated by an audio signal which corresponds to an audible warning signal such as a whistle or a siren. The modulated signal is then utilized to modulate a carrier signal and amplified and transmitted so that the radios in vehicles in the immediate area will receive an audible interference signal regardless of the particular channel to which the radio is tuned. The audible interference signal may be an intelligible reproduction of the input audio signal so that the driver of the vehicle can determine whether the warning signal is generated by a train whistle, a siren or a human voice.