In recent years, sophisticated audio systems have been installed on touring motorcycles. One feature of these systems is the provision for headphones on or inside the safety helmets. With such an installation, the rider must still be able to perceive safety-related sounds, such as the siren of an emergency vehicle. This paper considers the spectral characteristics of sirens and ambient motorcycle noise, and the sound attenuation of helmets in general. This leads to the specification of characteristics for an audio filter which attenuates the program amplitude in the spectral region of a siren. The result permits the rider to hear a siren with adequate warning, yet maintains the desired high level of sound quality.