Still in the room is not the same as still moving
The lights go out while you are reading. You wave an arm, they return, and ten minutes later it happens again. The sensor may be doing exactly what its rule asks. The rule has mistaken a lack of detected movement for an empty room.
PIR stands for passive infrared. This common type of sensor detects changes in infrared energy as a person moves through its detection zones. It does not count the people sitting in the room. A timeout is simply how long the system waits after the last detection before taking action.
Note when the problem happens, where you are sitting and whether a door or furniture blocks the sensor. That gives a much better starting point than repeatedly increasing the timeout. In a passage, a short visit and a quick switch-off can make sense. In a study, the system needs to allow for someone being quietly occupied.
The rule may be asking the wrong question
If the rule says “no motion means nobody is here”, an occupied room can go dark. Increasing the timeout may help, but it does not address every cause.
Look at placement before adding complexity
Check what the sensor actually covers after furniture and doors are in place. Test the activities that cause trouble, including sitting still. Different sensing technologies and models have different strengths; buying a “presence” label is not enough.
I separate arrival behaviour from the decision to switch off. Useful additional inputs may help, but a pile of unreliable signals just creates a more complicated guess.
Make the mistake recoverable
Give people an obvious manual control and a way to keep the room lit. A quiet study needs a different policy from a passage.
Then test again under ordinary conditions. The target is comfortable use, not the shortest possible timeout.