listening post 
noun
1A station for intercepting electronic communications.It has a number of what it calls ‘intercept stations’ or listening posts around Australia for doing that, of which the biggest is at Shoal Bay near Darwin, and it's focused on Indonesia....
- Its listening posts capture virtually every electronic conversation around the world, Frost claims.
- At the apex of the listening network is Echelon, the US-led satellite spying system that taps into worldwide telecommunications with the help of listening posts stationed in Britain and all corners of the planet.
1.1A point near an enemy’s lines for detecting movements by sound.On the night of 14 May 1918, they were part of a five-man patrol on duty in an advance listening post along the front line....
- Infantry platoon command posts used small field switchboards and wire lines to connect squads, sentries, and listening posts.
- During the Cold War, the U.S. established a super secret underwater listening post at Midway in an attempt to track Soviet submarines.