Yes, there have been loads of people doing similar things! ESPHome already has a tutorial covering exactly this!

I’m writing this up because the approach that I ended up taking was not the intended/planned approach.

The Geiger Counter

I originally pulled the trigger on this particular version because it had a built in screen attached to a micro controller.

I naïvely thought that I’d be able to get a simple UART from the 4 pins next to the microcontroller or maybe even get data directly off of the micro USB port.

Millimeter Wave technology has recently hit “mass consumer product adoption” price points. A casual search for “human presence sensor” on Ali Express will turn up a seemingly endless number of sub $40 devices that can detect movement far more accurately than any old PIR sensor.

Each listing is fairly generic; there’s no explicit manufacturer details but they all use the same marketing images:

As the photos below will show, neither device is super well marked with a model number so I’ll just refer to each by either the color of the enclosure or by the radar sensor inside.