There is no technicality behind the term "Gaydar" as it is supposed to make a person know the possibility of another person's sexual orientation through a few indications which are completely physical, sexual, and emotional. Of course, many dating apps developed a little technical factor added to this term to know whether a person belongs to the queer community or not, only when the other person also uses the same platform to find his/her interests. But what if the person whom you find attractive out of nowhere and randomly, don't use such technical platforms or dating sites? How come you get to know the preferences of that particular person?
It's hard for a person to randomly guess the other person's sexual orientation or preference and it's uncivilized if you guess it wrong and make a big fool out of yourself. This is the time; you must listen to your heart, not your brain. This is the time you must be emotional instead of technical. This is one of the problems in the queer community. Have you ever found a man very attractive and thought many times before approaching him, just because you are not sure whether he is also into men or not? This happens to all of us, especially gays, lesbians, and bisexuals.