Sentry Gun is the first upgrade of path 1 for the Monkey Engineer in Bloons TD 5 Deluxe, Bloons TD 5 Mobile, Bloons Monkey City and Bloons TD Battles Mobile that allows it to create sentry guns within its range. The Sentry Guns shoot nails, and each nail can pop 2 bloons. It is very useful for the early rounds as it acts like several Dart Monkeys all attacking at once. The Monkey Engineer can create up to 3 Sentry Guns with no fire rate upgrades when he is upgraded to this. However, the Engineer can produce more sentries if it's under the influence of a Jungle Drums Monkey Village, M.I.B. Call to Arms ability, or if the Fast Engineering and/or Sprockets upgrades are bought.
A Monkey Engineer with the sentry gun upgrade
Sentry Gun named as a "Sentry"
Sentry Gun named as a "SentrySprockets"
BMC icon of the Engineer with this upgrade
Sentry Gun upgrade icon in BMC Flash, with several discounts
- Sentry Guns can be sold for $0, and also have a target priority which can be changed. Often Sentry Guns would only be sold to give space for another tower to be placed on.
- They are effective on daily challenges and special missions where the amount of towers is limited, as they do not affect your total tower count.
- Sentry Guns are created every 10 seconds and have a lifespan of 25 seconds.
- The target priority of a sentry will be the same as the target priority of the engineer who spawned it. (tested in BMC and BTD5 Deluxe)
- When you upgrade the Engineer to Sprockets, any new sentries spawned will have the name "SentrySprockets". These sentries are not affected by Monkey Knowledge. (tested in BMC)
- In the mobile versions, the sentries are instead internally upgraded 0-3.
- The Sentries actually might be based off of the Sentry Turret from Valve's Team Fortress 2.
- When a sentry runs out of time, it explodes. The explosion is visually the same as the Splodey Darts one from BTD5.