A:Answer Antonio- We are sorry that you are having issues with your existing RM5764HD. This unit is a non-expandable unit. You cannot add or replace the baby unit that came with it. We would like to know more about the issue, please contact VTech Customer Support for further assistance at 1-800-595-9511. We are open from 9:00 AM to 3:00 PM, Mondays through Fridays. When calling, please have your model number handy:RM5764HD. Thank you! - VTech Support