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, Bloons TD Battles Mobile, and Bloons TD 6 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 upgraded to this. However, the Engineer can produce more sentries if it's under the influence of other towers such as Jungle Drums Villages or additional upgrades such as Fast Engineering/Faster Engineering.

Tips

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 the total tower count.
Sentry Guns are created every 10 seconds and have a lifespan of 25 seconds.
In the case of BTD5 Deluxe, Bloons Monkey City Flash and BTD6, Sentries' target priority is determined by the Engineer who has spawned them. In BTD5/Battles/Monkey City Mobile, however, Sentries default to First no matter what target priority the Engineer has.

Similar to BTD5, Sentry Guns can be sold for $0. Fortunately, Sentries don't have Footprints and can allow towers to be stacked on top of them.
They are helpful in Daily Challenges and Advanced Challenges where the amount of towers is limited, as they do not affect the total tower count.
Sentry Guns are created every 10 seconds and have a lifespan of 25 seconds.
- Lifespan increases to 30 seconds with necessary MK.
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.

When you upgrade the Engineer to Sprockets, any new sentries spawned will have the name "SentrySprockets". These sentries are not affected by Monkey Knowledge in BMC Flash.
- In the mobile versions, the sentries are instead internally upgraded 0-3, and are affected by Knowledge in BMC Mobile.
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 it has in BTD5 and Battles, causing the sentries to spawn anywhere, including on the track, water and unplaceable spots.
When a sentry runs out of time, it explodes. The explosion is visually the same as the Splodey Darts one from BTD5.