Auto Start

 (Non-Stop in Bloons Monkey City and Auto Round Start in Bloons Tower Defense 5 Mobile) is a "speed option" that debuted in Bloons Monkey City and was later released for Bloons TD 5 Mobile. It also returns in Bloons TD 6. Auto Start, when turned on, automatically begins the next round after all bloons in the previous round have been popped. Spike Factory piles disappear when the next round starts, as usual, unless an upgrade specifically stalls this.

Bloons Monkey City
Non-stop in Bloons Monkey City was originally a extension of the fast forward button which made rounds both a little faster and non-stop. This is still in effect for Bloons Monkey City Mobile.

It is now a little box next to the "Go" button that, when ticked, rounds go non-stop, and when not, rounds go normally. This is better because you can go non-stop at normal speed. There is currently no hotkey to tick the box.

Bloons TD 5 Mobile
The option to turn on the non-stop in Bloons TD 5 Mobile can be found by opening the settings menu by tapping the gear icon on the bottom right.

Bloons TD 6
The option variant returns from Bloons TD 5 in a heavily similar fashion. However if you are selecting a tower, the sub-menu for the tower will not go away unlike in past games except for Bloons Monkey City. The Auto Start functionality can be accessed from the pause menu.