my 4 cats  

Well, the cats know that the playpen is pretty safe, but the ferals feel safe out there and tend to rocket thru when we flush them inside.

Some are a bit wary about who might be lurking on the other side of the flap, so they might peek thru first, but honestly, I wouldn't know who's coming and going by the way they use the flap.

My cats wait for a human to open the door. We don't have a cat flap because of living in the complex, but I remember when the bedroom door was gone for one night, the cats had to inspect the door to make sure it was really gone. Then when they realized it was gone they timidly would walk in/out of it.