As a number of settlements both big and small have started walling themselves off completely I'd like to see some kind of door bell implemented so that visitors can announce their arrival without needing a local on their kin list. I imagine that any town with an idol would be allowed to build them within their area of influence and when rung they would be heard by anyone within the towns area of influence. Alternatively you could allow anyone to build them and make it so they can only be heard from within a certain radius.
I imagine you would have to make casts and pour the metal to make the bells, the bells could then be used in the construction of certain buildings. You could even make it so you select the note the bell chimes in.
Edit: There are of course other possible uses for bells.