Abstract: A method and apparatus for warning a motor vehicle operator of an approaching emergency motor vehicle having a sounding siren. The method comprehends selecting two frequencies A'-B' that fall within the siren frequency range and providing a microphone for detecting the sound signals including the siren signals and filtering out the electrical siren signals by a band pass filter. The selected A' and B' frequency signals are individually detected to provide output indications thereof representative of an A'-B' frequency transition. The output indications are processed for determining the preselected number of frequency transitions and producing a warning signal representative of the approaching emergency vehicle. The warning signal is utilized to give the motor vehicle operator an audible alarm and/or a visible alarm and deenergizing the motor vehicle's sound system.