That or you can just listen for tire noise. Even electic cars are quite loud above 25 mph, or so, so it only really becomes a problem at stop lights. Even then, the distinctive power supply whine will let youn that a hybrid or electric is behind you.

Agreed about tire noise and whine, but the problem is level of ambient noise, and habit. If you have an IC car nearby, even idling, the electric one will be virtually silent.

A revving engine would be less disruptive. It's a noise that most of us filter out, except those in situations which make them on alert for oncoming traffic, e.g. pedestrians and cyclists.

Quite true. Also, my brain reacts to "on your left" by assuming that I can let my guard down, which would be the wrong reaction if it's a car.

This seems like the perfect use for something like a mini LIDAR you can mount on a bike that detects a car behind you and just lights up a couple of LEDs on the handlebars.

Forget the bike, I've always wanted a kit that would detect cars around my car and display them like a mini map. Maybe with high speed delta from my own highlighted.

I mostly bike around cities, and when I drive I have taken to cracking open a window because not being able to hear cars around me feels deeply disconcerting.

Wow - I thought it was just me !

Every cyclist has their own preferences, but for me, a rear view mirror really helps. I still turn and look if I have to change lanes or something like that, but keeping an "inventory" of what's behind me really helps avoid unnecessary surprises.