TTY

A text-based telecommunications device that enables people who are deaf, hard of hearing, or have speech disabilities to communicate over telephone lines by typing messages that are displayed on a screen or printed on paper. TTY devices were the primary means of telephone communication for deaf individuals before the widespread adoption of text messaging, email, and video relay services. The technology uses acoustic couplers or direct connections to transmit typed text as audio tones. TTY compatibility remains a legal requirement under the ADA for emergency services (911) and public accommodations, though usage has declined significantly with the rise of mobile devices and internet-based communication. The terms TTY and TDD are often used interchangeably, though TDD specifically refers to devices for deaf users while TTY is the broader category.