Best presence sensor

As title suggests, I'm working on a project where I'll put some sensors inside a chandelier to control appliances, and I was wondering which sensor would be the best, given that it must work in different light conditions and differently sized rooms. I have little to no experience with these sensors so I really don't even know which factors should I take into account. Any help would be greatly appreciated.

What criterion do you have for "best"?

Eh, good question :D I need these sensors to detect the presence of one or more persons in the room (either moving or not moving), and possibly exclude smaller moving objects (animals, etc).

Usually they use PIR sensor as detector, sometimes IR-cam

But what if the sensor is behind a traslucent surface such as the one in a chandelier, and doesn't 'see' the actual people in the room? Wouldnt it be better to use some volumetric sensors or similars?

Volumetric will works only if people create a noise or talking, PIR doesn’t have such limitness.

Apparent motion is detected when an infrared source with one temperature, such as a human, passes in front of

I think he means a sensor of the whole volume when he says volumetric sensors not an audio sensor. Something like an ultrasonic flood that normally returns a static value with no one in the room and any room disturbance shows a change, rather like some car alarms work. The problem will be eliminating

smaller moving objects (animals, etc).

I don't think that can be done.

What about the size of the room? I think those car alarm sensors work exactly cause the total inner volume of a car is rather small. Will they work for bigger spaces? Any info about them?

the problem is that this sensor must be mounted almost inside/really close to any lightbulb in the room.

Will they work for bigger spaces?

The principal is the same you just might need to drive more power into the ultrasonic transmitter. However there is no plug and play solution for what you want to do you are going to have to experiment.