A lot of different things happen during a car crash, none of them good and several of them loud. Mercedes-Benz is trying to offset that noise:
When your ear hears a sudden loud noise, the acoustic reflex contracts the stapedius muscle in the middle ear to block out the sound, protecting the sensitive eardrums and other bits of the inner ear.
Mercedes has taken advantage of this in the E-Class, with a new feature called Pre-Safe Sound. When the car senses an imminent impact (using onboard cameras and ultrasonic sensors), the stereo plays a loud static-type noise around 85 decibels. It’s not so loud that it hurts, but it’s loud enough to trigger the acoustic reflex and protect the ear from the much louder sound of the accident that arrives a moment later.
This strikes me as eminently more useful than, for instance, the recent tendency of automakers to pipe engine noise into the cabin.
(Via The Truth About Cars.)