The device, which emits a humming sound similar to an electric motor, will be available on the third-generation Prius in Japan beginning next week. The aim is to "alert but not annoy," according to a Toyota press release.
Toyota spokesman David Lee said the company plans to begin offering the device in other markets, including the United States, at some point in the future. But he could not say when.
The device is designed to meet new safety requirements in Japan for gasoline-electric and other hybrid vehicles that are much quieter than traditional gas powered cars.
The ¥12,600 ($149) device automatically kicks in when the Prius is running on its electric motor at speeds up to about 15 miles per hour. The sound is similar to the hum of an electric motor, but louder. It rises and falls in pitch relative to the vehicle's speed to help pedestrians locate the car.