When in the vicinity of a female who is deemed fuckable by one, a sensation will be felt in one's body indicating the urge to fuck said female.
The overall detection field is based on many factors: Length of dry spell, satisfaction level of last fucking, hotness of female, age of one who is using cock-dar, experience with females, and experience in use of the cock-dar. In rare occasions, the overall detection field can be affected by one's swagger.
Of course this list does not contain all factors, for the anatomy of each male is different, meaning that different factors will apply to and affect different men.
Guy 2: Asian girl at 12'o'clock!
Guy 1: Cock-dar detecting 5 females of fuckable status within the vicinity.
"That one? Ew. He's not even cute."
"Hmm, yea, but he's sending my cockdar off the charts."
"I know my cockdar is telling me that guy has a big penis, but I hate him for it because he's just a cocky fucker. Literally."