I found an old intercom phone that I decided would be perfect as the ringer for my doorbell. Low voltage electricity is super easy to deal with — it’s probably still a good idea to turn off the breaker, but it’s not nearly as zippy as the rest of the electricity in your house.
Just take the housing off the outside of your doorbell ringer and unscrew the base from the wall. Just unhook the two wires and remove the ringer. The back of the old intercom (or telephone) will have two wires also. It doesn’t matter which two you attach, so just attach the wires on the intercom to the wires in the wall and attach the intercom to the wall. If all goes well, when you press your doorbell the phone will ring! (You could use any old telephone you wish.)