> We implemented the WiKey system using a TP-Link TL-WR1043ND WiFi router and a Lenovo X200 laptop. WiKey achieves more than 97.5% detection rate for detecting the keystroke and 96.4% recognition accuracy for classifying single keys. In real-world experiments, WiKey can recognize keystrokes in a continuously typed sentence with an accuracy of 93.5%.

More papers on keystroke recognition: https://scholar.google.com/scholar?hl=en&as_sdt=5%2C31&sciod...

60Ghz mmWave radar (coming to Wi-Fi via 802.11ay) has higher resolution, shorter range and low ability to penetrate building walls, but can pass through unshielded windows: https://news.ycombinator.com/item?id=30172647.