There is also a history of maintaining zombie sounds long after technology has made them obsolete. On smartphones, for example, the actions of locking the device or taking photos are often accompanied by the noises of a mechanical lock or camera shutter. In financial apps, transactions are often accompanied by the sound of jingling coins or a cash register.

In the case of hybrid and electric vehicles, though, the need for sound is about more than the user experience: It’s about safety. About a decade ago, the National Highway Traffic Safety Administration found that hybrid electric vehicles were 35 percent more likely than those with internal combustion engines to be involved in a pedestrian accident. Hybrids were also 57 percent more likely to be involved in accidents involving bicycles.

In 2010, Congress passed a law to enhance pedestrian safety, instructing the agency to craft a rule mandating that hybrid and electric vehicles emit noise. The rule was finalized in 2016 and requires that such noises be produced when the car is driving at speeds up to 30 kilometers per hour. Above that, tire, wind and other noises were warning enough, it deemed. The move was celebrated by the blind community.

Automakers requested a few changes, though, including allowing owners to choose from a range of sounds rather than just one. On Tuesday, the agency proposed making that tweak, and said that it would accept input on the move until November.

Regulators around the world have been imposing or weighing such requirements. In the European Union, for example, one such rule just took effect in July.

As a result, major carmakers have been working on crafting sounds to meet those requirements. Jaguar, for example, said it worked for four years on the futuristic noise for its I-PACE SUV. For the 2020 model of the Chevrolet Bolt, General Motors designed the vehicle’s sound in-house, using a quiet electric whirring as a starting point, according to Todd Bruder, the engineer who led development of the sound.

“It wants to be purposeful, it wants to be pleasing, but also have the ability to warn people that there’s something coming,” he said.