Sentry Gun (BTD5)

“	Creates temporary sentry guns and deploys them nearby.	”
	^{~ Official Bloons TD Battles Mobile description.}

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 she 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.

Costs

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.
The BMC Mobile sentry is missing the "OnlyTargetPlacementLocations": true line of code, causing the sentries to spawn anywhere, including on the track and on water.
When a sentry runs out of time, it explodes. The explosion is visually the same as the Splodey Darts one from BTD5.