To wire a doorbell, connect the transformer to the 110-volt wiring from the home's circuit panel, then connect the low-voltage side of the transformer to the button switch and the second wire to the doorbell. Use a separate wire to connect the remaining screw on the switch to the remaining terminal on the doorbell.
Doorbells generally operate with a 10-volt transformer, while door chimes operate at 16 volts. When changing from a doorbell to a chime, it is necessary to change transformers. However, many doorbells have a built-in transformer, eliminating the need for a separate installation. Some of these units have a standard power plug that works with household outlets and eliminates the need for hardwiring the transformer to household power.
It is possible to use the same transformer to operate a doorbell for the front door and a buzzer for the back door. Some chimes offer the option of different tones for the front and back doors in a single unit.
Before working on any electrical wiring, including doorbells, ensure that the circuit is off at the circuit breaker panel. Test for live circuits by touching the probes of a circuit tester to the black and white wires that supply power to the transformer from the panel.