How far/long does the owner have to be away from the AirTag before it can be detected by others? I noticed my neighbor had an AirTag on his dog one day and so

How far/long does the owner have to be away from the AirTag before it can be detected by others? I noticed my neighbor had an AirTag on his dog one day and so we tried to detect it with my Android Phone using the App and never could. To the stalking concerns, if the AirTag doesn't think it's lost then it doesn't chirp. It also seems to remain undetectable to others. Does that mean someone could put an AirTag on someone and as long as they are close by it won't alert others?