Increases the attack range of all towers within the beacon area. Has several useful upgrades that help out nearby towers, including its ultimate ability to call in Super Monkey Storms.
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 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). It has been replaced in BTD5 by the Monkey Village.
Upgrades (BTD4)
Wider Influence: Increases the range of the Monkey Beacon, allowing it to affect more towers.
425/500/540
Jungle Drums: Increases the attack speed of all towers within the beacon's radius.
1275/1500/1620
Sonar Beacon: Allows towers in its radius to detect camo bloons.
240/280/300
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.
2975/3500/3780
Notes
Super Monkey Storms destroy all Bloons up to Ceramic Bloons. M.O.A.B.s and B.F.B.s need low HP to be destroyed by Super Monkey Storms. In Bloons TD 4 Super Monkey Storm has a reload time now; about 1 and a half minutes. In BTD3, there wasn't any reload time. The reload time was created due to the upgrade's great power. Without it, later rounds (+80) are ridiculously easy. Also, it is unique, so you can only have 1 Monkey Storm Beacon.
This is the second tower to be an upgrade, first being the Spike-O-Pult.