I do it using MMWave sensor, 60Ghz one. Want to have more of them but installation is a pain as these need to be mounted on ceiling so WiFi based sensor would be awesome!
replies(2):
"Inside a $1 radar motion sensor" (2024), 100 comments, https://news.ycombinator.com/item?id=40834349
"mmWave radar, you won't see it coming" (2022), 180 comments, https://news.ycombinator.com/item?id=30172647
"What Is mmWave Radar?: Everything You Need to Know About FMCW" (2022), 30 comments, https://news.ycombinator.com/item?id=35312351
But not all of them are good for doing stuff like this.
You need full raw I/Q and DAC access to sweep the frequency.