Mirrors are great, but most bikers don’t have them. And even then it might still be your ears that alert you that there’s a car behind you (electric or not — I still hear them), after which you can keep tabs with your mirror.
I don’t understand why everybody’s so happy to discount ears in this thread. Haven’t they been vital to our survival since forever? Yes eyes are more important in this case, but I’ll take whatever sensory aid I can get on my morning commute..
Audio cues are less and less useful as electric vehicles become more popular. (I am a city biker and there are plenty already.)