I'm writing a new feature and I'm not sure how to handle this.

If the script is essentially the blueprint for the film, should I be trying to trick the reader?

The situation is this, I have a voice coming from another room which is a recorded voice The 'twist' is that it's not the real person, on screen this will be obvious when it's found out, but in the script do I write it as O.S. essentially tricking the reader or do I go straight for V.O. in which case the reader will know something else is going on.

Currently I'm writing it as O.S. until its found by the characters to actually be a V.O. and then I change it to that.

Thanks in advance.

I had a similar question a few months ago (there is a thread but I don’t know how to hyperlink it here).
I think you should keep it as O.S., as at this point we believe it’s a voice in the other room. Yes trick the reader!  Use all the tools in your possession to make a compelling screenplay.

I think if you mean to trick your character AND the viewer watching the movie, then also trick the reader. O.S.

O.S. for sure.

Ditto to what Jeff and Steve and Hyperactive said.  

Thanks all, will leave it as is.

Just to add, as a guideline you write the screenplay as the audience would experience it. So you don't give away any twists until the moment the audience would experience it also. Thus, the O.S. until the moment it is revealed it is a recorded voice.

Cheers, Mark.

Definitely what I'm sticking with.

Not sure how this would ever be a V.O., even once the twist is revealed?

O.S. is anything that's part of the "world" of the screenplay that the audience doesn't see, and that would include a recorded, non-human voice.

V.O. is narration, or the inner thoughts of a character, which doesn't "exist" in the world you're creating, and is meant to speak directly to the audience and not the other characters.

Quoted from ajr Not sure how this would ever be a V.O., even once the twist is revealed? O.S. is anything that's part of the "world" of the screenplay that the audience doesn't see, and that would include a recorded, non-human voice. V.O. is narration, or the inner thoughts of a character, which doesn't "exist" in the world you're creating, and is meant to speak directly to the audience and not the other characters.

I think we have a slightly different understanding of V.O. vs O.S.

I'll definitely be going with my version.

A quick Google search gave me this:

"V.O. is used when the speaker is not physically in the scene. The speaker could be someone on the other end of a telephone line or radio broadcast, an unseen narrator, or a character’s inner-monologue."

A radio broadcast is part of the world and isn't that different to what I have.

Phone conversations are speaking directly to the character and not the audience and are also formatted as voice overs.

Correct, I don't think I explained myself properly - phone calls and radio broadcasts are written as V.O. and are part of the world of the screenplay - I guess what's confusing me about your example is that you have a voice coming from the other room, written as O.S., and only the nature of the voice changes, not the proximity to the scene... ?

Quoted from Warren I'm writing a new feature and I'm not sure how to handle this. If the script is essentially the blueprint for the film, should I be trying to trick the reader? The situation is this, I have a voice coming from another room which is a recorded voice The 'twist' is that it's not the real person, on screen this will be obvious when it's found out, but in the script do I write it as O.S. essentially tricking the reader or do I go straight for V.O. in which case the reader will know something else is going on. Currently I'm writing it as O.S. until its found by the characters to actually be a V.O. and then I change it to that. Thanks in advance.

I would go with O.S. From your premise, I'm assuming that your character (let's call him John) is hearing the voice of someone from the other room (let's call her Jane) and even though it's a recorded voice - it's tone, etc make it seems like a real voice to John.

To add more misdirection (again not sure of the premise) I would even have the voice as a character (e.g., maybe John looks at a picture of JANE - then it's JANE (O.S).

Make sure you hit me up for a read when you're done. I owe you a ton
  

Yeah, OS, would be correct here. The VO is OS, after all. Yes, you should be trying to trick the reader. I find it way more entertaining when a writer messes with my expectations.