Can you say what products make use of this technique? i.e. is it well known like Juniper Mist or not publicly available?

Verizon has a security feature built around this, https://www.xfinity.com/hub/smart-home/wifi-motion

Philips WiZ bulbs: https://www.wizconnected.com/en-us/explore-wiz/spacesense

Alarm.com also supports such sensors: https://poweredbyalarm.com/eventresources/wp-content/uploads...