From my understanding, Wi-Fi sensing requires at least two antennas (transmitter and receiver) to measure signal disruption. This could be one device with both antennas, or two separate devices.

There are also techniques that use one controlled device and leverage ambient Wi-Fi signals from uncontrolled sources (like a neighbor's router), but TOMMY explicitly disables all options for using devices outside your own network. It only works with ESP32s you've flashed and added to your system.