Abstract: A horn and actuator circuit particularly useful in connection with selective actuation of a horn located onboard a model railroad train as the train transverses a selected section of track wherein the horn is selectively actuated and deactuated by a magnetic field of selected polarity located at the track and where the horn assembly includes a magnetic field detector to detect the magnetic polarity most recently received to actuate and deactuate the horn means. The horn means can include at least one oscillator adapted to generate a square wave pulse of selected frequency and can include one or more additional horns to generate square wave pulses of a second frequency as well as arrangements where the output frequency and intensity of an oscillator is modified to provide a sound of variable frequencies and intensity simulating a steam whistle.