In August 2010, Toyota began sales of an onboard sound device to mimic the sound of an electric motor when the Prius is operating in its most quiet mode, as an electric vehicle at speeds up to approximately . The device became available in Japan for retrofitting on the third-generation Prius at a price of (~) including the consumption tax. The alert rises and falls in pitch according to the vehicle's speed, to convey the vehicle's proximity and movement to nearby pedestrians. The device met the Ministry of Land, Infrastructure, Transport and Tourism issued in January 2010 for hybrid and other near-silent vehicles. Click this link for a video showing a demo of the warning sound at different speeds.
