Officers in Oregon city, Ohio, praised the caller's quick thinking, which led to the alleged abuser being arrested.

The unnamed woman told local media her mum was being attacked at the time.

This tactic for subtly calling the emergency services has been internet lore for years, but this is a rare confirmed case of it being effective.

Officials have previously warned that the strategy is not guaranteed to work, as dispatchers are not trained to recognise a pizza order as a genuine call for help.

The dispatcher who answered the call, Tim Teneyck, told local news station 13 ABC he initially thought the woman had dialled an incorrect number.

When she insisted she was through to the right person, he realised what was happening - partly because he had seen similar scenarios being shared on social media.

"You see it on Facebook, but it's not something that anybody has ever been trained for," Mr Teneyck said. "Other dispatchers that I've talked to would not have picked up on this. They've told me they wouldn't have picked up on this."

What did the caller say?

Here's a transcript of the conversation.

Mr Teneyck: Oregon 911

Caller: I would like to order a pizza at [address redacted].

Mr Teneyck: You called 911 to order a pizza?

Caller: Uh, yeah. Apartment [redacted].

Mr Teneyck: This is the wrong number to call for a pizza...

Caller: No, no, no. You're not understanding.

Mr Teneyck: I'm getting you now.

Later in the call, the woman found creative ways to answer Mr Teneyck's yes or no questions about how much danger she and her mother were in, and what services they needed.

Mr Teneyck: Is the other guy still there?

Caller: Yep, I need a large pizza.

Mr Teneyck: All right. How about medical, do you need medical?

Caller: No. With pepperoni.

Where does the pizza idea come from?

It is unclear where exactly the idea originated, but a very similar scenario was used in a campaign by the Norwegian Women's Shelter Association in 2010.

Four years later, in May 2014, a user on discussion website Reddit claiming to be a 911 operator described a domestic abuse victim calling to order a pizza. They wrote that the call "started out pretty dumb, but was actually pretty serious" - before describing a conversation similar to the one Mr Tenyck had.

A few months later a number of news sites reported on the Reddit post, and in 2015 it was even turned into a Super Bowl ad addressing domestic abuse.

The scenario later became a viral "public service announcement" on social media, with one Facebook post making the unsubstantiated claim that "dispatchers are trained" to recognise the pizza call as a call for help, and to ask specific questions.

This claim was debunked last year. Christopher Carver, the dispatch centre operations director for the National Emergency Number Association in the US, told the Associated Press that police are not trained to listen out for any specific code words or scenarios.

"Setting any expectations of secret phrases that will work with any 911 centre is potentially very dangerous," he said, and recommended that people use 911's SMS service instead.

But the "Text to 911" service is not available in all US locations, and is not functioning in Oregon city in Ohio.

Mr Carver did say that dispatchers would not hang up on a caller. The priority, he added, is for callers to let the dispatcher know their location.

What can people in the UK do?

People who need to make a discreet call to 999 - the UK's emergency services number - can do so using the British police's "silent solution" system.

A 999 caller can remain silent if they are unable to speak. Then, when prompted, should key in the number 55 to silently inform officers that they are experiencing a genuine emergency.

If the situation is violent, callers can also call 999 and leave the phone off the hook so that operators can hear what is going on. In most cases, dispatchers will be able to trace the location of the incident from the call itself.