We must be able to differentiate a phone playing a sound and a car by hearing alone, and that very quickly. We need a sound similar to emergency vehicle sirens

We must be able to differentiate a phone playing a sound and a car by hearing alone, and that very quickly. We need a sound similar to emergency vehicle sirens but obviously less loud and dramatic. So it is very important to have a universal class of sounds, and it must be forbidden to play sounds of that class on a street for other things.