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Bloons Wiki
For the BTD5 version of this upgrade, see Sentry Gun (BTD5).
Creates temporary sentry guns and deploys them nearby.
~ Official Bloons TD 6 description.

Sentry Gun is the first upgrade of path 1 for the Engineer Monkey in Bloons TD 6. It allows it to create sentry guns within its range every 10 seconds. Each sentry lasts for 25 seconds, meaning on average up to between 2 and 3 sentries from the same Engineer become active at a time. The creation of sentries is affected by attack speed buffs such as Jungle Drums Villages.

The Sentry Guns shoot nails every 0.95 seconds, and each nail can pop 2 bloons (3 with Oversize Nails) and they have a range of 45 (+4 with Larger Service Area). The nails are of the sharp damage type and cannot pop lead or frozen without special upgrades. Crosspathing with Oversize Nails changes the sentry damage type from sharp to shatter (sharp + frozen-popping).

It costs $425 on Easy, $500 on Medium, $540 on Hard, and $600 on Impoppable.



Sentry Gun is traditionally the main feature of the Engineer that gives him the edge at early-game, and it remains true in BTD6. In essence, the Sentry Gun upgrade provides the Engineer with an attack that allows him to deploy nearly statistically equivalent 0-0-1 Dart Monkeys nearby. These sentries give the Engineer with considerable early-game damage, especially while combined with the fair attack speed and pierce of the base Engineer himself.


  • Sentries spawned from the Engineer will automatically be set to whatever the Engineer's target priority is. They can also be manually changed to a specific target priority.
  • It's usually best to start crosspathing once further upgraded to Faster Engineering, as increasing the production speed further is far more effective than range or pierce crosspathing in most situations.
  • It is worth a note that adding Sentry Gun effectively increases the attack range coverage of the Engineer Monkey somewhat, although this is dependent on the where the Engineer's sentries may land.

Version History[]

When first released, sentries had very little popping power, especially in relation to 0-0-0 Dart Monkeys, which now have 2 pierce instead of 1. The base sentry pierce was increased back to the BTD5 amount to compete with the value of 0-0-0 Dart Monkeys. Additionally, Sentries now have crosspathing benefits in later updates.
12.0 (compared to BTD5)
  • Nerf Pierce of Sentry Gun decreased (2 → 1).
  • Buff Standard Sentry pierce increased from 1 to 2.
  • Buff 110 Larger Service Area now applies 1/5th the range (+4) to any sentries produced.
  • Buff 101 Oversize Nails allows sentries produced by this tower to pop frozen Bloons.
  • Buff 101 Oversize Nails now increases sentry pierce by +1.

Ninja Kiwi stated in the 20.0 Patch Notes that the reasoning behind these changes was "continuing our efforts to make crosspaths meaningful" and to "fit the style of each path more solidly".

  • Buff 120 Deconstruction now applies to sentries.

Bug fixes[]

Mostly just fine-tuning for special cases.
  • [Bug Fix] 110 Larger Service Area now increases Sentry deploy range.
  • [Bug Fix] Nerf Fixed a bug where Bloon Trap granted camo detection and lead poppage to sentries.
  • [Bug Fix] 1xx Sentry Gun sentries no longer gain camo detection when a save is loaded.
  • [Bug Fix] 1xx Sentry Gun sentry placement will no longer ignore 'smart placement' if the Engineer cannot reach the track.


Official artwork[]


  • Before the sentry pierce buff in Version 15.0, Sentries were the slowest one-projectile towers to have only one pierce, excluding Sniper Monkeys (their bullets are too fast to be visibly moving in-game).