The safe zones at present are pretty clear cut, always in specific rooms. So the rooms entrance is where the gramophone is effective from.
We don't plan on having the gramophones out in open areas, they will always be tucked inside smaller rooms :)
If it causes confusion we can perhaps add a glowing line to the ground to further highlight it. But for now they are sufficient.
However thank you for that suggestion and that would certainly be a great tool for us to be able to place gramophones out in open areas if we ever needed to do that. Multiplayer survival modes perhaps.