"His graduate assistant at the time then devised a switching device called the "cheek switch." Attached to his glasses, it could detect, via a low infrared beam

"His graduate assistant at the time then devised a switching device called the "cheek switch." Attached to his glasses, it could detect, via a low infrared beam, when Hawking tensed his cheek muscle. Since then, Hawking has achieved the feat of writing emails, browsing the internet, writing books and speaking using only one muscle." https://www.wired.com/2015/01/intel-gave-stephen-hawking-voice/ https://www.wired.com/2015/01/intel-gave-stephen-hawking-voi...