This is a hypothetical. I watched a YouTube video of a woman who was visited by the police after her husband made searches on Google for pressure cookers. Someone responded by saying that's unlikely and it did indeed turn out that he made those searches on his work computer which his employee was monitoring with a keylogger software and then reported his suspicions to the police.
When it comes to a person making a dozen suspicious searches from their home into Google, can this place them on a watchlist or not? Assuming they are just for research