Regular presence detectors (MDT 4 zone presence detectors, 120€ each) for the bigger rooms with some additional single zone detectors( mostly MDT as well around 75€) for some special applications (e.g. Sofa). Used those as well for some really small rooms (loo,etc.)

For the home office rooms and general presence in the bedrooms we used Steinel True Presence (around 300€ but includes air quality sensors - in the end they aren't much more expensive if you plan on measuring air quality there anyway). They are dumb in terms of positioning in the room but superior for detecting people who do not move for a long time.

In addition to these I have normal KNX motion detectors(mostly MDT for about 90€) for some areas (as mentioned elsewhere: Next to the bed at ground level to detect your motion when you get up at night and switch on the light with 5% red so the wife does not wake up)

In terms of how it works:

Presence detectors (excluding the Steinel) are basically pimped infrared motion detectors. They detect your signature against the background and unlike motion detectors kind of remember your signature for a while. Each one has one or more "zones" it can detect you in. The "minis" mentioned above have one, the 4 zone ones have,well,four which are aimed at 45,135,225,315 degrees in case of the MDTs. This allows the detector to basically differentiate between someone being "in my right upper corner", "in my left lower corner" etc. (Especially as detection ranges can be varied between zones but also for various applications and even day/night mode).

With a bit of clever positioning e.g. my presence detector in the kitchen has four zones: at the stovetop, workspace one and workspace two and "entry". The detector sits on the ceiling right where these zones meet (which is not the middle of the room in this case!)

If anyone registers a presence the normal light goes on (when it's dark enough). If you go into workspace one (where most cutting is done) the under-kitchen-cabinet light goes on. The sensitivity for that is much smaller as I don't want it to go on if you just pass through, though. Additionally the sensitivity of the "entry" is smaller as I don't want the light to go on if someone just passed the kitchen in the hallway.

The Steinel works a bit different as it is radar based and has only one zone, but is therefore able to recognise ones breathing movements/minimal movement while e.g. working. Otherwise it works the same.

The additional ones I use are there to recognise people better, e.g. my living room is fairly big and I want the system to specifically recognise people being on the sofa so the mini looks straight down only - while the big 4 zone detector is only able to see if people are "in the direction of the sofa".

Hope that describes it somewhat, let me know if you have any questions!