There was an article somewhere that I read about them trying different sounds to see which was the preferred choice ..... they settled on a Jetson's saucer air computer sound, but observes noted that the ones who actually did hear it, looked up, not around them for an approaching vehicle .....
I like the stealth approach to someone who clearly isn't paying attention to their surroundings, get close enough it feels like the car is about to touch them, then hit the horn ...... rabbit in the headlights comes to mind and after they land, return home for fresh undies, I feel they will pay a lot more attention in the future .... either that or I'm installing a few dash cams so I can record the event from multiple angles and start a You Tube channel ..... "do you recognise this muppet?"
T1 Terry