"its like a bullet, you don't hear the one that hits you"
Was doing a shore dive with my son looking for...fossilized sharks teeth of all things. We had surfaced and were discussing whether to keep looking or swim the 300yds back to shore. About that time my son says in an excited voice "I just saw a dorsal fin". We made pretty good time back to shore. The visibility was about 4 feet.
i always thought it would be cool to develop 360 degree sonar a diver could wear to detect approaching fish
but then constant steady beeps might just guide them in