How to check if something is in an Area2D?

There is a signal that fires when something enters the area and a signal that emits when something exits the area. Implement a state flag that is set on enter and cleared on exit. You can then query that flag at any time to check if the thing is in the area or not.

How do I do that?

I figured out how to do this with the help of hyvernox from in this post.