The Monkey Beacon is a tower that appears in BTD3 and BTD4, it costs the same as the Banana Farm and doesn't attack. It costs $850 on Easy, $1020 (BTD3)/$1000 (BTD4) on Medium, and $1080 on Hard. It improves any towers in its radius, beginning with range (be careful when upgrading as the effect of Jungle Drums cancels out when you upgrade them to sonar despite that Super Monkey Storm still makes towers detect Camo Bloons, proving that the jungle drums canceling out is a bug). Its hotkey is N in BTD4. Its BTD5 counterpart is the Monkey Village.
Wider Influence: Increases the range of the Monkey Beacon, allowing it to affect more towers.
Jungle Drums: Increases the attack speed of all towers within the beacon's radius.
Sonar Beacon: Allows towers in its radius to detect camo bloons.
Monkey Storm Beacon: The final upgrade (Unlocked at rank 18) is the monkey storm beacon, which summons monkey storms by paying the amount of cash required to use it. And you can only have one Monkey Storm Beacon.