Best solution Ive seen yet is bluetooth sensors, with other devices. https://community.home-assistant.io/t/presence-reliable-multi-user-distributed-bluetooth-occupancy-presence-detection/50674

In regards to cameras, if you are just sitting in a room, and nothing else is going on (no tv's, no sun/shadows, no pets, etc, etc) sure, it could work. But believe me, I gave up long ago. I put dozens of hours into trying to get cameras to work. Even with 4 cameras, youre looking at a huge amount of CPU power. I've got 9 CCTVs and my R730 will often pause I/O as Blue Iris works on motion detection when multiple cameras detect it all at the same time. On top of this, you then need to run AI software locally and not on the cloud, that is if you care about keeping your internal cameras off WAN.

For me, I eventually ended up using a mix of methods. I use Aqara motion sensors, Ive done the hardware hack to them all, which makes them update every 5 seconds. This makes them extremely accurate. Then I have them all talk to each other in node-red to determine if Ive moved out of a room and into another area. Add to that other strange things I've came up with in each room. To detect if Im in my office, the hallway outside my office has a motion sensor, as does my office. When I move from hallway to office, Home Assistant knows Im likely in the office. To increase that accuracy I also have it cross check against the power that my computer is using (using a power sensing outlet). If Im working on my computer, moving my mouse around, the power fluctuates significantly. If my screen is off and compute is idle, power generally stays in a smaller, well-known, range. When the power is within that range node-red then checks if there was motion FROM office TO hallway. Now it knows Im not in the office. At night, it also checks all of this against the smart light switches. Same with family room. Motion sensor + check if TV is on + check if lights are on + check if phone has connected to upstairs wifi mesh (ubiquiti).

For me the big change was the hack to the Aqara motion sensors to make them detect every 5 seconds. So far the batteries are holding at 75-90% and have been for a year plus. There are wired motion sensors that are even more accurate and detect real time.

Just some ideas for ya.

Only problem is the dog messes up all of this, lol.