Prior research in 2004: https://www.semanticscholar.org/paper/Keyboard-acoustic-emanations-Asonov-Agrawal/134ee2914659ce442ea2f2740d9cc512bde4442f https://www.s

Prior research in 2004: https://www.semanticscholar.org/paper/Keyboard-acoustic-emanations-Asonov-Agrawal/134ee2914659ce442ea2f2740d9cc512bde4442f https://www.semanticscholar.org/paper/Keyboard-acoustic-eman... "We show that PC keyboards, notebook keyboards, telephone and ATM pads are vulnerable to attacks based on differentiating the sound emanated by different keys. Our attack employs a neural network to recognize the key being pressed. We also investigate why different keys produce different sounds and provide hints for the design of homophonic keyboards that would be resistant to this type of attack."