I had to go with 24 volt because I have multiple entries which means multiple doorbells drawing power. Especially at night when IR clicks on. With 1 doorbell you are fine with 16. Pick up a ring pro at bestbuy, take off existing doorbell, connect the 2 wires, if it powers up and connects to app and says voltage is green, you're good to go. Don't need electrician or climbing in attic.