There are numerous systems in which disc brakes indicate that they are approaching their wear limit by making a screeching noise.
Today’s invention resembles this technique but is in the form of a recordable surface on one’s brake discs, not unlike an old LP record played by a stylus.
As an electric vehicle or bicycle nears pedestrians standing on the pavement it should slow down. The braking would thus alert people not to step off the pavement.
Drivers and riders could record a personal message, in their own voice, saying eg “My blue bike is approaching. Look both ways!”