Life
The Technology That Let Stephen Hawking Work
How did Stephen Hawking write papers and books once he could no longer move or speak? A deep dive into his wheelchair, his cheek-switch, the ACAT software and the Intel collaboration.
Last reviewed 23 May 2026 · How we research
One of the most remarkable aspects of Stephen Hawking's life is simply this: how did a man who could not move or speak continue to do world-class physics, write bestselling books, and deliver lectures for decades? The answer is a story of human ingenuity and a long partnership between Hawking and the engineers who kept him communicating.
The early years: a thumb and a clicker
After Hawking lost his voice to a tracheotomy in 1985, he first communicated by raising his eyebrows to pick out letters on a spelling card. Soon after, a Californian engineer named Walt Woltosz sent him a program called Equalizer, which let him select words from a screen using a hand-held clicker. For a time, while he still had use of his hand, this is how he composed everything, including much of A Brief History of Time.
The cheek switch
As the disease progressed and he lost the use of his hand, a new method was needed. Engineers fitted an infrared sensor to his glasses that detected movements of a single muscle in his cheek. By twitching that cheek, Hawking could select characters and words on his screen. It was painstaking: in his later years he could manage only a handful of words per minute, yet with it he wrote books, scientific papers and emails.
ACAT: the Intel collaboration
The computer system on his wheelchair was maintained for many years with the help of the chip company Intel, which supported him from 1997 onward. In his final years Intel's engineers built him a new platform called ACAT (the Assistive Context-Aware Toolkit), which used predictive text, similar in spirit to a smartphone keyboard, to speed up his communication by guessing the words he was likely to want. Intel later released ACAT as open-source software, so that others with similar conditions could benefit from the work done for Hawking.
The voice
Running through all of this was the famous synthesised voice, a 1980s American-accented system he chose to keep even when far more natural voices became available, because it had become part of his identity. The full story of the voice is told on its own page.
A partnership of decades
What this technology represents is not just clever engineering but a sustained human effort: a series of people and companies who, over more than thirty years, devoted themselves to keeping one of the world's great minds in conversation with the world. It is also a powerful example of what assistive technology can achieve, explored more generally in the context of motor neurone disease.