Looking on the internet deeply has found these results:

I'm watching a movie in the hall is the most popular phrase on the web.

I'm watching a movie at the hall 154,100,000 results on the web	I'm watching a movie in the hall 1490,000,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
Watching a movie on my phone, 'cause I'm hiding from my son. Actually, we were thinking about getting out of the house and watching a movie at Wyatt's. I can't believe I'm a director with a movie at Sundance. If you don't mind, I'm watching a movie, and I don't have Tivo. No way. I'm not going to be the mother that plays a movie at a birthday party. I think everybody's down the hall watching a movie or something. I'm here to study, which means I'll be watching a movie on my iPad, so let's agree to not bother me. I'm watching a movie, and I don't have the Tivo.	Haven't seen a movie in forever. Besides, we're already watching a movie in the car. I'm here to study, which means I'll be watching a movie on my iPad, so let's agree to not bother me. Watching a movie on my phone, 'cause I'm hiding from my son. I'm watching a movie, and I don't have the Tivo. If you don't mind, I'm watching a movie, and I don't have Tivo. No way. I think everybody's down the hall watching a movie or something. They're watching a movie in the lecture theatre.

I'm watching a movie at the hall

154,100,000 results on the web

I'm watching a movie in the hall

1490,000,000 results on the web

More popular!

Watching a movie on my phone, 'cause I'm hiding from my son.
Actually, we were thinking about getting out of the house and watching a movie at Wyatt's.
I can't believe I'm a director with a movie at Sundance.
If you don't mind, I'm watching a movie, and I don't have Tivo. No way.
I'm not going to be the mother that plays a movie at a birthday party.
I think everybody's down the hall watching a movie or something.
I'm here to study, which means I'll be watching a movie on my iPad, so let's agree to not bother me.
I'm watching a movie, and I don't have the Tivo.

Haven't seen a movie in forever.
Besides, we're already watching a movie in the car.
I'm here to study, which means I'll be watching a movie on my iPad, so let's agree to not bother me.
Watching a movie on my phone, 'cause I'm hiding from my son.
I'm watching a movie, and I don't have the Tivo.
If you don't mind, I'm watching a movie, and I don't have Tivo. No way.
I think everybody's down the hall watching a movie or something.
They're watching a movie in the lecture theatre.