By Kenneth Macdonald
BBC Scotland Special Correspondent
Security cameras have long been a fact of Scottish life, viewed with relief by many communities and with suspicion by civil libertarians.
But what if they were listening to you as well? It has already happened in Glasgow.
Sigard can tell aggressive voices from other loud noises
A Dutch company called Sound Intelligence carried out a two week long trial in a busy city centre street.
They stress that their system, called Sigard, does not record conversations. It listens not to what is being said but how it is being said.
At the company's headquarters in the Dutch city of Amersfoort, Bram Kuipers explained that Sigard was listening for the changes that affect the human voice in an aggressive situation.
"It's a different state that you are normally in," he said.
"You're full of adrenalin and your voice gets distorted. You start to scream and you try to impose on someone."
Identifying such changes comes naturally to the human brain.
But teaching a computer system to recognise the specific characteristics of aggression has taken more than a decade, building on research at the University of Groningen.
Bram Kuipers explains how the system operates
Sound Intelligence say Sigard is able to discriminate between the sound of aggression and other, everyday loud noises like passing trucks and car horns.
Kuipers demonstrated this by clapping his hands. A display screen noted the sounds but took no action. Then he shouted aggressively. This time an alarm sounded and a CCTV camera spun round to look directly at the source of the shouting.
Such systems are already in everyday use on the streets of several Dutch towns and cities. The company said it also has uses in potential flashpoints like prisons and benefits offices.
There are hopes eventually to sell Sigard in other markets - hence the Glasgow trial.
"We installed a couple of microphones in one of the main streets of Glasgow," Kuipers said.
"It's working. We detected aggression and it's currently under evaluation."
I'd rather people trialled them in a more open way so that people know what going to be out there
Patrick Harvie MSP
Sigard is one aspect of what can be considered the next generation of CCTV technology. Other innovations are also on the market, among them talking cameras and systems to detect suspicious behaviour patterns.
But the co-leader of the Scottish Greens, Patrick Harvie MSP, is sceptical of the spread of new surveillance technologies.
"It's probably fair enough to trial them. But I'd rather people trialled them in a more open way so that people know what going to be out there and we all have a bit of control over it," he said.
He thinks more visible solutions such as mobile CCTV units are more effective in preventing violence.
Meanwhile Sound Intelligence say they have yet to install a permanent Sigard system in Scotland.
But the next time you get the feeling Big Brother is watching you, perhaps he will be listening as well.
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