Spring loaded, slides up and down about an inch...
When the screen door is shut, you slide that shut to keep bugs out. If you need to open the door you push down on it and it presses the screen door lever to open the door.
OH MY GOSH! I love this forum! I have had my camper about a year, and I had no idea I could press down on the round piece and open the screen without having to slide it back to open the door! who knew!!! (well, y'all did!)