2021 BRN Discussion, page-1573

This looks like one of Socionext's radar patent applications for detecting humans:

https://worldwide.espacenet.com/patent/search/family/064456406/publication/WO2018220701A1?q=socionext%20radar

WO2018220701A1 INFORMATION PROCESSING DEVICE AND DETECTION DEVICE
a distance spectrum is calculated based on a beat signal which is a difference between a transmission wave which is a frequency-swept radio wave transmitted by a sensor and a reflection wave of the transmission wave received by the sensor, A calculation unit configured to calculate a time series waveform indicating a temporal change in intensity of the distance spectrum with respect to each distance from the information processing device, and a detection unit configured to detect respiration of the living body based on the time series waveform .

24 GHz has a 12.5 mm wavelength, so they must be measuring phase change or somesuch to detect breathing.

Check out Figure 6 which shows the example of the kids in the people-mover.

On the battery-saving, a 1/1000 duty cycle reduces the power consumption by that ratio (approximately). So 0.5 mW at 1:1000 = 0.5 W for 1/1000. sec. My guess would be that this is a clocked operation rather than a sleep/wake operation.

The transmitter uses a lot more power than the receiver, but processing the received signal will use additional power.