I'm not sure how other players would feel about this (or how difficult it would be to implement) but what do you think about making it so speakers with the "Global playback" option selected will be audible from inside a building (or speakers inside a building are audible from outside, or inside another building etc.)

I use speakers to alert me to conditions like low accumulator charge, but I often miss the alert because I'm working inside a building. I don't know anything's wrong until I see the lights dim.

Global playback across surfaces is to my knowledge not supported by the modding API. The "Show alert" setting in speakers, however, shows you an alert on every surface. If you have the habit of tuning alert messages out because vanilla spams too many of them, I recommend turning the unimportant ones off with the /alerts command.

Ah, okay. I guess I'll have to turn the alerts on.