Sexual orientation:

One person may presume knowledge of another person's sexual orientation based upon perceived characteristics, such as appearance, clothing, tone of voice, and accompaniment by and behavior with other people. The attempt to detect sexual orientation in social situations is known as gaydar; some studies have found that guesses based on face photos perform better than chance. 2015 research suggests that "gaydar" is an alternate label for using LGBT stereotypes to infer orientation, and that face-shape is not an accurate indication of orientation.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". What is a term for someone who tries to determine someones sexuality?
gaydar