Select a doorbell intercom unit that does not require you to run bell wire from intercom to intercom. Running wires from intercom to intercom requires you to drill holes and fish wire throughout each intercom. Selecting a doorbell intercom unit to work with your existing doorbell sidesteps having to perform those tasks. Doorbell intercoms allow you to talk with whoever is at your door from inside your home. You do not have to answer the door to verify who is knocking.
Shut off the power to your home's doorbell at the main circuit box by flipping the switch to the "off" position. Test to verify the power is shut off by pressing the button on your doorbell. If you hear the doorbell ring, the power is not off; consider shutting off power to the entire home.
Remove the doorbell button by unscrewing the screws holding it in place with your screwdriver. Disconnect the wires from the terminals.
Attach the new doorbell mounting bracket with the screws provided and your drill. Fasten the top screw first and verify the unit is plumb and then fasten the bottom screw.
Install the doorbell module by attaching the wires to the terminal screws on the back of the module. Transfer the wires from the terminals to the new AC adaptor that came with your doorbell intercom.
Plug the adaptor into a 120-volt receptacle. This links the doorbell module to the circuit to carry the signal to the intercom monitor.
Disconnect the doorbell chime or bell. Remove the doorbell or chime cover and unscrew the terminal screws and remove the wires. Twist the bare ends of the wires together with your hands and secure by twisting on small wire nuts. Replace the cover as the doorbell no longer works.
Fasten the intercom monitor to the location of your choice with the screws provided and your drill. Hang the unit in its place and plug the cord into the 120-volt receptacle.
Restore the power by flipping the switch in your home's main circuit box to the "on" position. Test the unit by pressing the button on the outdoor unit. The unit should produce a sound resembling a gong.