Keyer

Semi-automatic keys were an innovation that had an impulse driven, horizontal pendulum mechanism that (only) created a series of correctly timed "dits".

When the lever is released, springs push it back to center and break the switch contact (including the resetting the oscillating pendulum).

(Modern electronic keyers create both the "dits" and the "dahs" automatically, as long as one of the switches is in contact, and are called "fully-automatic".)

Keys built for side-to-side motion would not aggravate nor cause the injury, and allowed disabled telegraphers to continue in their profession.

This is an early instance of a multi-key user-input device, as are computer keyboards (which, incidentally, are what one uses for modern RTTY).

[1] A keyer differs from a keyboard in the sense that it lacks a traditional "board"; the keys are arranged in a cluster[1] which is often held in the hand.

These systems were developed primarily for use in early, experimental forms of wearable computing, and have also been adapted to cycling with a heads-up display in projects like BEHEMOTH by Steven K. Roberts.

One type of these, the so-called half-QWERTY layout, uses only minimal chording, requiring the space bar to be pressed down if the alternate hand is used.