How about in this context from the series Prison Break season1, episode1 that an officer and a new inmate are talking together?
inmate: Come again?
officer: I said, are you being a smartass?
inmate: Just trying to fly low, avoid the radar, boss. Do my time... and get out.
officer: There isn't any flying under my radar.
inmate: Good to know.
An airplane which is flying low, flying at a low altitude, cannot be detected by radar. We say the plane is "flying under the radar". People watching the radar screen will not notice it.
We use this as a metaphor. He doesn't want to do anything that will cause himself to be noticed like get into fights, cause trouble, etc.