Range is a game mechanic in the BTD series. It is the limit of where a tower can detect bloons to attack. It is signified by a dark circle around towers. Contrary to popular belief, the range is not the limit of where it can attack but the area where it can detect bloons to attack. The range of a tower is independent from how far the projectile(s) can reach.
Because range increases the tower's detection of bloons, it can change the angle at which towers can attack from. This is especially the case for upgrades such as Juggernaut and Crossbow, which benefit from straight lines.
A very important tip is to make the dark circle touch the map's path. If this wasn't made, the tower won't be able to attack Bloons. The exceptions are towers with infinite range. For these towers, there is little worry about them not attacking Bloons, so feel free to place them where ever you like. There is an exception though, in BTD6.
In Bloons TD 6, a tower's range can be restricted by sight-blocking objects in the track, by a feature called "Line of Sight". This applies to both limited range towers and infinite range towers. For example, if a bloon is in a Super Monkey's range circle, but the bloon is behind a rock and the tower can't "see" it, the Super Monkey won't attack the bloon. Areas where sight is blocked in BTD6 are colored red.
There are two distinct types of range: detection range, and projectile range. Detection range is the range that the tower can detect bloons and therefore can trigger its attack(s). Projectile range is dependent on projectile lifespan, and it is normally approximately +25% of the detection range assuming normal projectile speed. The Tack Zone, Blade Maelstrom, and Grape Shot are examples of the stark differences between projectile range and detection range.
Before Bloons TD 4
Prior to Bloons TD 4, the range is always shown by a white circle when interacted by the player. Bloons are always detected by their centerpoints. For Monkey Beacon, the range determines which towers get influenced by its buffs.
In Bloons TD 4
Several new towers now have unique range functionalities that are different from the usual range system. Examples of this include Monkey Ace, Mortar Tower, and Banana Farm. Some of these have "dummy" ranges, the only exception being Monkey Ace in that game; these ranges are purely for display purposes. Dartling Gun was introduced later on as another immobile tower with a "dummy" range but infinite on-demand aimable targeting.
In Bloons TD 5
The Sniper Monkey has infinite range, making it the first offensive immobile tower to have a "dummy" range. Advanced Intel was introduced in BTD5, the first tower to make use of other towers' ranges to expand its own range. Some towers and upgrades allow mobility, Heli Pilot joining Monkey Ace as the only towers with mobility by default, and Aircraft Carrier being among the first upgrades to grant a mobility option.
In Bloons TD 6
In Bloons TD 6, the range of a tower determines the range at which it can attack bloons. As with all previous games, a tower's range is indicated by a dark circle when interacted by the player. There is a new game mechanic called Line of Sight that prevents most towers from attacking over obstacles with Line of Sight. Some towers naturally ignore line of sight, while certain upgrades can remove Line of Sight restrictions for the tower.
Some attacks have infinite range, a classic example being Sniper Monkey and a new example being Inferno Ring's meteor. Other attacks simply have more range than their displayed range shows, an example being Sticky Bomb's sticky bomb, which has precisely 50% more range than current range of the Ninja Monkey with said upgrade. Attacks with infinite range are marked as Full Map Range , while attacks with more range than the given range but not infinite range are marked as Extended Range , both for purposes of gameplay research on Bloons Wiki.
Most towers detect bloons by detecting the bloon's hitbox. If any significant part of the bloon's hitbox overlaps with the tower's range, the tower will attack the bloon. There are a few towers that will only detect bloons' centrepoints however, and those have the property Target Bloon Midpoints.
When it comes to Tower Buffs with limited range, such as a Monkey Villages or Shinobi Tactics, the middle of a tower's footprint must be detected within the range of the buffing source in order to gain a tower buff.
In Bloons TD 6, the range of an entire in-game map is approximately 286 units wide.
In Bloons Adventure Time TD
In Bloons Adventure Time TD, the range of a tower functions quite differently from the other Bloons TD games. Unlike BTD6 and before, towers can only attack bloons if the tower can reach the section of the track where the bloons are present, and thus exhibit the Target Bloon Midpoints property. This means that towers will refuse to attack MOAB-Class Bloons (which are wider than the track) if the towers cannot reach the portion of the track that the blimp is flying over, even if the blimp itself is clearly in range of them.
- Monkey Villages don't attack using range until upgraded to High Energy Beacon. Instead, they help support all towers within its range.
- The Pontoon Pro does not grant a range boost to the Meerkat Spy.
- The Super Monkey can attack bloons slightly out of it's range.
- If a bloon is off the map, but there is a tower with enough range to see the bloon if it is on the map, then said tower will attack the bloon. This doesn't happen with towers that have unlimited range, except for the Ray of Doom. However, Sniper Monkeys may attack bloons that are "off" the screen but haven't leaked yet.
- In Bloons Tower Defense 5, the range circle will go above towers when you place a tower near another tower. However, in Bloons Tower Defense 5 Deluxe, the circle will go below the tower, making Temple of the Monkey Gods harder to fit together.
- The highest finite range possible in BTD5 is the Temple of the Monkey God upgrade with Epic Range with a 1/x Monkey village, Tier 2 Super Monkey Lair activated, and on a Pontoon Pro. In BTD5 Mobile, it would be the same, except the Temple of the Monkey God would be replaced with a Temple of the Vengeful Monkey.
- In relation to the Advanced Intel upgrade for the Monkey Sub, infinitely ranged towers have their circle as their range.
- All towers can attack MOAB-class bloons slightly outside their range. This is because MOABs are bigger than standard bloons.
- The range circle for towers could be turned off in Bloons TD 6 by the "Line of Sight" option, for performance purposes. This was the only BTD game that has this option. This option has however since been removed.