Geckos (yea, I know, anoles) come in through the vinyl siding in a screened lanai ( obviously only if if you have siding) as well as under the "sweep" of the screen door. They hide there until you open the door.
I used this sliding screen from Lowes and it works great. 2 small openings on the bottom but I blocked them with white tape. Took me 20 minutes to install once I realized the wheels sat ON the track and not IN the track. There is a video online detailing the install.
LINK TO LOWES SCREEN
Last year "screen companies" wanted $300-$400 to do the same thing for me.