HCO
Hearing carry over (HCO). A form of TRS where the person with the speech disability is able to listen to the other end user and, in reply, the CA speaks the text as typed by the person with the speech disability. The CA does not type any conversation. Two-line HCO is an HCO service that allows TRS users to use one telephone line for hearing and the other for sending TTY messages. HCO-to-TTY allows a relay conversation to take place between an HCO user and a TTY user. HCO-to-HCO allows a relay conversation to take place between two HCO users.