One of the less-known cool facts about the Gestapo counter espionage was their wireless triangulation strategy. They actually had Gestapo agents in civilian clothes roaming around Brussels and other occupied European cities, hoping that a spy would be broadcasting nearby so they could pinpoint the location. They carried a suitcase full of radio equipment and a small earpiece so they could point the suitcase to different directions and hear where the signal was coming from. These agents would then flag the building or even a specific apartment for an immediate and brutal raid.
It was really an endless cat and mouse game they were playing, and one where smart spies - known as "pianists" by the Gestapo - would keep their radio broadcasts short and sweet.
Silence is golden, especially on radio.