Carmakers face a new problem with EVs, which are so quiet in operation that they can be dangerous for pedestrians and fellow drivers alike. The fully-electric autonomous robotaxis that Zoox is developing (and planning to deploy on public roads soon) present a similar problem, albeit twofold, as the Amazon-backed AVs need to emit sounds that are simultaneously soothing, yet firm enough to make passengers listen for important audio cues in the cabin.

So, Zoox hired classically-trained musician Jeremy Yang to come up with a new sound profile for its robotaxis, meant to combine a relaxing soundtrack with insistent beeps and boops to convince users to buckle up, or fully close a door that’s ajar, as Wired reports. That balance of soothing and annoying has been hard to master, but the company believes it has successfully done it by evoking airy synthesizers with an “ambient hum” in the cabin — broken up only by prompts that convey increasing levels of urgency based on the situation.