I'm at the Museum of Communications in Seattle, to answer a question:

in old Hollywood films, when someone is on a phone call and they got hung up on,

why did they hear a dial tone?

[dial tone]

"Well, you can stick your well-laid plan up your well-laid ass." [dial tone]

Supervision is the word that describes how a telephone switch

knows whether the calling and called parties are on hook or off hook.

When you end a call and hang up,

the equipment receives that on-hook signal,

and anything that was in service at that time

disconnects and goes back to its normal state.

So you end up with dead air.

Now, the reason that a sound director would use a dial tone

instead of just nothing is kind of obvious, right?

It's to make it clear that the other side has hung up.

That's certainly what lots of people argue online.

Except they could just do that by using one short sound effect.

And sometimes, they do.

"Don't ever call me again."

[rattling click]

"Wow!

I...

I guess you're home."

"Good luck."

[rattling click]

It turns out there's another reason.

Back in the days of celluloid film,

southern California was one of the few places in America

with independent telephone companies,

not part of the giant Bell monopoly that handled the rest of the country.

Well, behind us is a step-by-step system

and it's a relative of the telephone systems

that were used in most of southern California.

The Bell system didn't have as much of a monopoly there.

As I dial a number, various elements of the step connect me

through the system from start to finish.

And that's where it got the name step-by-step.

As I finish dialling, the call will connect...

[ringing]

...and it can be answered.

Now, in the step system, it doesn't have what's called 'far-end supervision'.

And that means that the called party can hang up and pick up again

as many times as they want, and the call won't disconnect.

But if the calling party hangs up...

[dial tone]

...the called party will get hit with dial tone right away

because the system doesn't know whether I've been hung up on

or whether I've just picked up the phone.

So in Hollywood, where all of the movies were being written and filmed,

their experience on the telephone was actually different

from most of the rest of America, and the world.

Which, let's be honest, is kind of like so many other things in Hollywood.

The bottom line is:

the folks making the movies really did get a dial tone when they were hung up on,

at least sometimes, so they put that in their films.

Or they picked whichever option worked best for the scene.

If it's still happening when a character uses a cell phone, though?

That's just lazy.

Thank you to all the team at Seattle's wonderful Museum of Communications!

You can check out their YouTube channel over here

or pull down the description for a link to the Museum and to see their opening hours

and a list of all the incredible equipment they've got here.