The sensor array emitted a scanning pulse every forty seconds over a range of ten light years. A pulse was designed to track warp fields and impulse signatures. It was possible for a starship to lower its power output below the detection threshold of an array.
In 2375, the USS Voyager attempted to silently pass a sensor array on its route to the Tehara star system; however, the attempt failed and the array transmitted an alert, which was received by two Devore warships. (VOY: "Counterpoint")