Telecommunications Device for the Deaf

A specialized device that enables text-based telephone communication for people who are deaf or hard of hearing. TDDs transmit typed text over telephone lines using acoustic coupling or direct connection, requiring compatible devices at both ends of the conversation. While TDDs provided essential telephone access from the 1960s through the 1990s, they required both parties to have specialized equipment, limiting their utility for calling hearing people without TDDs. The technology has been largely superseded by SMS text messaging, email, video relay services, and real-time text (RTT), which offer communication with anyone regardless of specialized equipment—an example of mainstream technology eliminating the need for dedicated assistive devices.