The radar or "sixth sense" someone gets when they sense that two people have recently hooked up. Often times this is due to the people being overly friendly with each other, overly infatuated, or simply just awkward with one another.
This is very common with coworkers, or 2 people of the same group of friends.
Coworker 1: Man, did you see Jennifer and James at the department meeting yesterday? They were totally awkward with each other. They both kept on laughing nervously and shifting their weight any time one of them said something, and James was sweating balls! They used to be really comfortable with one another. I bet they are hooking up.
Coworker2: Yea, my screwdar was going off too! I bet they hooked up after everyone left the company party last Friday. They seemed pretty plastered.