Electric vehicle warning sounds

Electric vehicle warning sounds are sounds designed to alert pedestrians to the presence of electric drive vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and battery electric vehicles (BEVs) travelling at low speeds. Warning sound devices were deemed necessary by some government regulators because vehicles operating in all-electric mode produce less noise than traditional combustion engine vehicles and can make it difficult for pedestrians and cyclists to be aware of their presence.

Source: Wikipedia — Electric vehicle warning sounds (CC BY-SA 4.0)