I have no idea if specialized tools can reliably detect AI writing but, as someone whose writing on forums like HN has been accused a couple of times of being AI, I can say that humans aren't very good at it. So far, my limited experience with being falsely accused is it seems to partly just be a bias against being a decent writer with a good vocabulary who sometimes writes longer posts.

As for the reliability of specialized tools in detecting AI writing, I'm skeptical at a conceptual level because an LLM can be reinforcement trained with feedback from such a tool (RLTF instead of RLHF). While they may be somewhat reliable at the moment, it seems unlikely they'll stay that way.

Unfortunately, since there are already companies marketing 'AI detectors' to academic institutions, they won't stop marketing them as their reliability continues to get worse. Which will probably result in an increasing shit show of false accusations against students.