Everyone knows about the automobile daytime running lamps. They help the pedestrians to see an approaching car.
Maybe it's time to test another one, based on sound. But the drivers cannot to honker often.
The work principle of the device offering here is about sending two ultrasound (unhearable) waves ahead of the car.
These waves may be very narrow and can be accepted only by people why are located on straightforward line the car is moving.
As they have different frequencies, say 100 kHz and 101 kHz, they can produce the resulting sound 1000 Hz in human ear.
Thus, one can hear somewhat like "beep-beep". This mean that the car is near and can cross the way.
Useful in dark, fog and other low-visible conditions, or when a human have a weak vision.
Nothing is invented here, just application of well known and applied for years physical and mathematical laws.