Besides allowing volume control, any such devices ought to offer the user a frequency component choice. Guess the idea of high frequency is that it’s more unusual, thus more alerting, and perhaps better able to be heard above low-frequency outdoor noise (trucks rumbling by, etc).
But I first got a clue to my hearing loss when our security alarm key pads got changed out. I complained to the security company that the volume of the alert to turn off the alarm on entering the house was so much weaker on the new key pads. That might have been true in part but I think the main thing was that the new keypad tone was just a purer, higher frequency whereas the manufacturer of the older keypad was smart enough to include some lower frequency components. So I’d be all for some tone settings options on any device alert, car or otherwise. Now that everything’s getting “smart,” it shouldn’t be too hard to provide for on devices on into the future.