#Followup to my prior #mmwave / #homeassistant post:

I've now been working with cheap #HiLink #LD2410 (as the name suggestions, 24Ghz) radar sensors that you can pick up on Amazon for $6/apiece.

These sensors are super impressive for their price-point.

Example; They all have a simple "Out" pin that is pulled high when a human is detected. That means you could build an entirely dumb object and use this sensor as a simple binary trigger.

Further example: You can provide the sensor power, drag the Out line to a relay and wire the relay into you bathroom fan (or light, or disco ball). Instantly, you have a fan that turns on when a human enters and turns off when they leave.

The LD2410's also feature Bluetooth which you use for firmware updates as well as configuring the sensor's parameters. (see attached images)

While not gravely concerning, I have some basic concerns about being able to fire up the config app and change settings if the sensor responds. However; BT range is limited and it's not on wifi\the internet or anything (#IOT security being what it is). So it'll likely end up as Security by Obscurity.

HiLink has a whole bunch of sensors in different configurations (https://www.hlktech.net/index.php?id=product&cate=RadarModule). Browsing their site it seems theyve got a 60Ghz module (4.9mm wavelength) for ~$12 and a facial recognition module for $10. Both sound like fun to play with. They also have the LD2461 which can track multiple bodies moving in a 3D space, but at $15/apiece I feel like most people don't need these capabilities above and beyond the LD2410 for providing occupancy. This is more like the hardware used for tracking individuals for advertising/marketing purposes.

Anyway! Back to the useful information;
The mmWave sensors work through glass and are not bothered by water/showers/rain. However, I'm almost certain that a body of water would pose an issue, but I don't have a pool to test with.

They will pick up your pets. That said, you might be able to mount a sensor at an appropriate height/angle and set the settings so that it's not a concern.

If you just want to have one of these; #ScreekWorkshop has been making and selling units that are compatible with Home Assistant out of the box.
However, they are also very cheap and easy to make if you have any experience using #ESPHome. Screek has a public repo for all their stuff, so you can even use their code as a starting point if you wanted. Super kind of them: https://www.screek.io/