I like the idea of adding another pilot tool for locating hidden ships, but don't think it should be as easy as a compass or anything else that says "ship this way" with no player input. That is why I keep bringing up ear trumpets. In fact, I just cobbled a tool concept together to illustrate what one could look like.
The concept starts in with this. Which is pretty silly looking.
I tore apart a gramophone model and made this.
Video link. The tool would work like the spyglass and range finder, being handheld and raised to the head when in use. You would be able to hear enemy engines and ambient sounds like guns reloading. Perhaps even muffled voices from voicechat. An experienced user could tell the difference between different ship types just by the sound. Standing near your own engines would diminish the tool's effective range. It could not mark enemies, and would rely on the user to convey location information.
Would it work in real life? Likely not. But neither would 100 ton ships supported by party balloons. Is it believable within the reality of GOIO? Yup. Looks like it would work, so it would.