Image copyright Getty Images

Peenemünde is a port in northern Germany, where the River Peene meets the Baltic Sea.

There, in October 1942, German engineers sat in a control room watching a television screen. It showed live, close-up images of a prototype weapon on its launch pad some 2.5km (1.5 miles) away. On another screen, with a wide-angle view, they saw the weapon surge skywards.

The test had succeeded. They were looking at something that would shape the future - but perhaps not in the way they imagined.

The V2, the Vergeltungswaffe or "vengeance weapon", was the world's first rocket-powered bomb, and it was supposed to win Hitler the war.

The weapon travelled faster than the speed of sound, so you did not know it was coming until it exploded. But, crucially, it could not be targeted precisely: the V2s killed thousands, but not enough to tip the scales of conflict.

Image copyright Getty Images Image caption V2 rocket attacks on London began on 8 September 1944

Wernher von Braun, the brilliant young engineer behind the V2, surrendered to the Americans as the Third Reich fell, then helped them win the space race.

If you had told him that his rocket test would be the first step towards putting a man on the Moon, he would not have been surprised. That is exactly what motivated him.

At one point, he was briefly arrested after someone on a train overheard him say that he wished he could build spaceships instead of weapons, and reported this suspiciously non-conforming thought to the Gestapo, the Nazi secret police.

But von Braun might not have anticipated that he was also witnessing the birth of another hugely influential technology - one the Gestapo would have loved in its modern form - closed-circuit television, better known as CCTV.

50 Things That Made the Modern Economy highlights the inventions, ideas and innovations that helped create the economic world.

It is broadcast on the BBC World Service. You can find more information about the programme's sources and listen to all the episodes online or subscribe to the programme podcast.

The pictures in that control room were the first example of a video feed being used not for broadcasting, but for real-time monitoring, in private - over a so-called "closed circuit".

The top brass at Peenemünde may have worked slave labourers to their deaths, but they had no intention of joining the fatalities. Instead, they invited television engineer Walter Bruch to devise a way for them to monitor the launches from a safe distance.

Image copyright Getty Images Image caption Electrical engineer Walter Bruch would also go on to invent the PAL colour television system

And that was wise, because the first V2 they tested did indeed blow up, destroying one of Bruch's cameras.

Exactly how popular Bruch's brainchild has now become is tricky to pin down. One estimate, a few years old, puts the number of surveillance cameras around the world at 245 million - that is about one for every 30 people. Another reckons there will soon be over twice that number in China alone.

It is certainly true that the market is expanding quickly, and its global leader is a company called Hikvision, part-owned by the Chinese government.

What is China doing with all these CCTV cameras?

Here's one example.

Picture the scene: you're trying to cross a busy road in the city of Xiangyang. You should wait for the lights to change, but you are in a hurry, so you make a dash for it, weaving through the traffic.

Image copyright Getty Images

A few days later, you might see your photo, name and government ID number on a huge electronic billboard above the intersection, outing you as a jaywalker.

But it is not just about the public shaming: surveillance cameras will feed into the country's planned "social credit" scheme. Exactly how the national system will work remains unclear, but various trials are using both public and private sector data to score people on whether they are a good citizen.

You might lose points for driving inconsiderately, paying your bills late, or spreading false information. Score high, and perks might include free use of public bikes; score low, and you might be banned from taking trains.

The aim is to encourage and reward desired behaviour - or, as an official document poetically puts it, "allow the trustworthy to roam everywhere under heaven, while making it hard for the discredited to take a single step".

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Perhaps this reminds you of a certain novel published seven years after Walter Bruch pioneered the surveillance camera.

In Nineteen Eighty-Four, George Orwell famously imagined a life where everything is monitored - not only in public spaces, but in people's homes. Everyone who is anyone must have a "telescreen", through which Big Brother can watch them.

But there is a hint in the story that these devices were originally something people chose to buy: when the duplicitous Mr Charrington needs to give Winston a believable reason for the apparent lack of a telescreen in his spare room, he says they were "too expensive", and "I never seemed to feel the need of it".

That sounds like the kind of conversation I have had recently about the voice-controlled smart speakers that some of the world's largest corporations would like to sell me, so I can ask about the weather, or say "Alexa, turn up my central heating", or automatically monitor what's in my fridge.

Image caption Voice-activated smart speakers capture ever greater amounts of data about us

The comic artist Zach Weinersmith sums up the value proposition like this:

"Can I put a device in your house that perpetually listens to everything you say and do, stores that information, profits from it, and doesn't give you access to it?"

"You'd have to pay me a lot."

"No. You'll pay us."

"Uh… pass?"

"The device can figure out when you're low on Cheez Balls and drone-deliver them in 30 minutes."

"Give me the machine!"

Devices like the Amazon Echo and Google Home have taken off because of advances in artificial intelligence - and that is the same reason behind the burgeoning demand for CCTV cameras. There are only so many screens at which one person can look.

But if software can watch and listen and decipher meaning, how much surveillance you can do is limited only by computing power.

Is it reasonable to feel a little queasy about this, or should we sit back and enjoy our drone-delivered Cheez Balls?

That depends in part on the extent to which we trust the entities that are watching us.

Media playback is unsupported on your device Media caption Amazon’s head of Alexa, Dave Limp, on privacy concerns

Amazon and Google hasten to reassure us that they are not snooping on all our conversations.

They insist the devices are just smart enough to listen for when you're saying the "wake" word - "Alexa", or "OK Google" - and only then do they send audio to the cloud, for more powerful servers to decipher what we want.

Then we have to trust that these devices are hard to hack - for criminals, and perhaps for governments. Of course, not everyone baulks at the thought of the state knowing more and more about our daily lives.

One Chinese woman told Australia's ABC that if, as her government said, every corner of public space was installed with cameras, she would feel safe.

Those who take a different view might be glad to know that CCTV is not yet as smart as it seems. The intersection in Xiangyang appears entirely automated - but actually the face recognition algorithms are not reliable enough. Government workers are sifting through the footage.

But maybe that does not matter. The perception of surveillance is enough to deter - fewer people are jaywalking.

That's the idea of the "panopticon": if you think you might be being watched, you will always act as though you are. It is an idea George Orwell understood perfectly.

So CCTV might still be a long way from living up to its technical potential. But for those who want it to change what we do or even how we think, that might not be such an obstacle.

The author writes the Financial Times's Undercover Economist column. 50 Things That Made the Modern Economy is broadcast on the BBC World Service. You can find more information about the programme's sources and listen to all the episodes online or subscribe to the programme podcast.