I'm trying to write a dialogue between two people on different sides of a locked door. I want to avoid but O.S. and split screen and show each character where they are when they're talking. How do I do this in a way that's easy to read? Apparently, you can't just follow a slug with dialogue and frankly, I don't want to muddy up the conversation with too many of those.

Coupla ways. If they are in a corridor then a doddle...

INT. CORRIDOR - DAY

Stanley and Ollie stand either side of a closed door. Stanley tries the handle - locked.

Ollie sees the handle turn...

OLLIE
That you Stan?

STAN
Ollie. Is that you?

OLLIE
No, I'm actually Pope Pius XI...

STAN
Oh good day your very holy holiness...


Alternatively you can start each scene if say one person is in a locked room. Then use INTERCUT or similar. You can do the same for phone calls should you so desire.

Then you can just run with the dialogue without (O.S.)
As loing as the reader can follow it there's no problem. Just state where each is and that the door is locked such as I showed above.

RV

INT. ROOM - DAY

A BANG on the door. JAMES looks up.

JAMES
Jonnyboy? Is that you?

INT. CORRIDOR - CONTINUOUS

JONNYBOY stands in front of James' door.

JONNYBOY
Yeah, it's me. This is how I'd format this scene.

INTERCUT between them either side of the door.

JAMES
Thanks! You're a genius.

JONNYBOY
I know, I know. Now you gonna let me in?

James considers for a moment.

JAMES
No.

You're having a problem with directing and editing. You write the blueprint and don't get hung up on that stuff. Just intercut as necessary. Bob's in the closet, Sally's outside trying to get in. INTERCUT BOB/SALLY and move on.