I live in an apartment.
If someone tried to enter while I’m entering using my fob, I ask them to show me their fob. If they can’t, I tell them they are trespassing.
That simple.
“I ask them to show me their fob. If they can’t, I tell them they are trespassing.”
No one in this incident were trespassing.
Had any one of the two people involved been trespassing, they would have been cited by the police.