These metal poles sit on a four-legged base, with the pole rising up to ten feet. At the top of the post are two dishes, one pointing one way, and the other pointing in the opposite direction. The receiving antenna inside the dishes blinks red, which reflects off the dishes.
The Listening Posts themselves are extremely easy to destroy, and are quite vulnerable to small-arms fire; however, it is advised not to stand too close because the explosion will harm anyone who is too close to it.
The South Korean government placed these Listening Posts throughout North Korea, as well as a small portion of China (in the northern province). They're aimed at intercepting Chinese plans for attacks on the South Koreans due to them having the same goal during the Song Initiative.
Listening posts can also be found in areas that are under the control of the AN and Russian Mafia, however, these are to a lesser extent due to those two factions not being direct enemies with the South Koreans. The Chinese will pay the mercenary $5,000 for each one destroyed and destroying them will also increase their favour towards you.
Similarly to Monuments, Blueprints and National Treasures, these are best utilised for their ability to quickly provide an improved standing from the faction (in this case the Chinese). If the player intends to work with all factions, doing South Korean contracts may make the Chinese hostile to the player and reserving listening posts for when needed to improve standing is a much better use than destroying them early.
The PDA says that there are only 55, but there are actually 56 in total.