What does "audio-countermeasure techniques" mean?
Are they techniques that make conversations on the phone inaudible?

“In a variety of assignments, both domestic and abroad, Mr. McCord has displayed
unusual imagination, ingenuity, and effectiveness in accomplishing his assigned tasks,” wrote one CIA official of the man who would, two years later, use those skills to break into the National Democratic Party’s headquarters in the Watergate. “His achievements in the fields of audio-countermeasure techniques and physical and technical security are particularly noteworthy…”