It means 1) to do something which is not noticed by those who are watching. and 2) to be hidden from view. The person wants their privacy.

It means "to avoid being noticed." RADAR is an acronym for RAdio Detection and Ranging. Originally it was a military system, designed to detect incoming hostile planes far away, in time to send up fighter planes to shoot them down. Because the sky is almost empty, a metal airplane in the sky is very obvious to radar equipment. However, close to the ground, there are thousands of buildings, towers, hills, trees, and other objects that reflect radar. Radar needs to be aimed a little bit above the ground or it will pick up too much "ground clutter." A plane that flies high will be detected. But a plane can escape detection by flying (dangerously) low, underneath the lowest edge of the radar beam.

before answering the question, you need to know what actually a radar does? "A radar is an electronic device which mainly used in airlines. Flights like domestic, international, war flights etc are determined by using the radars. Using a radar we can detect a plane, where it is or at which location or at what altitude, etc." There are many other uses, but I know this much only as of my knowledge. According to this you can answer to your question easily.