Is there a Doorbell already installed at this location
IF NOT, then you will need to tell the customer that
[say it this way!!] “I noticed that you do not have a doorbell already installed in your home. Because of this, We need to Install a special transformer and wiring in your home. Some older homes DID NOT have the wireing or the transform for a doorbell installed. The cost is $89 and that includes the parts & installation!” You might also recommend that they order a chime also.
CLICK HERE IF THERE IS A DOORBELL for the next step