Doorbells for apartment building??

[Jennifer Rysdam]

Have any of you had/put doorbells in your apartment buildings? I have an 8-plex and you have to knock SO hard on the doors for them to hear it that you end up with the neighbors coming to their doors too. I'm wondering if putting a wireless doorbell would work better. They would have to have enough frequencies that they wouldn't intercept each other, but I think it would be nice. Any thoughts???