Radar Scanner is the second upgrade on the second path for the Monkey Village in BTD5. It allows all the towers in its radius to detect and to attack camo bloons. It also increases the range of the Monkey Village in the flash versions of BTD5.
This upgrade is much more expensive than the Sonar Beacon upgrade in BTD4 ($280), which also allows towers in range to pop Camo Bloons.
The only difference between the two upgrades is the price and the fact that Radar Scanner increases range, while the Sonar Beacon doesn't.
Oddly, a "village radar scanner" is mentioned in the description of stage 3-1 of Bloons Super Monkey 2, even though the actual radar scanner village isn't seen.
The icon is a enemy radar scanner used on military ships to track the enemy similar how the radar scanner works, letting other towers detect camo bloons.