Looking for a better room area/proximity sensor

Is there a radar like sensor available? Something that can count large and small ‘blobs’ for human and animals in an area? I thought something like this existed that could ‘see’ through walls but I don’t remember what it was called and I may even be misremembering it altogether.

My end goal here is having it so when you leave a room the lights dim instantly instead of a timeout period. It would work with multiple users/people in a room. It could also differentiate between pets and humans.

I have used PIR sensors and I have good luck with them. I was curious if there was a way to take this sensor to the “next level.” I know there are ways to setup multiple sensors so when one is triggered it triggers another light to go off. With how my home is laid out I am not sure if I could devise such a method.

I have considered bluetooth sensors integrated with a few Raspberry Pi’s but this is limited to the device you have with you. This seemed to be a major disadvantage.

I have also considered an IR camera but that may get expensive and I am uncertain if it is ideal or if there is something better.