In the wake of last week's attacks in Paris, cities around the world are looking at how they can better protect their people.
One option is an increased use of so-called smart systems - networks of sensors and cameras that monitor citizens and their activities, raising alerts when threats arise.
One such technology on display at the Smart City Congress in the Spanish city of Barcelona this week was a gunshot alert system called Shotspotter.
As part of an effort to combat gun crime, networks of audio sensors have been installed on rooftops in more than 90 cities, mostly in the United States.
These monitor the sounds of the city and are able to identify the acoustic fingerprint of gunfire.
Within seconds of the shots, the system is able to send a recording of the shooting, along with the precise details of its location to the police.
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European cities are now also considering how it can be used to help them to respond to threats - in much the same way a fire alarm works.
"In the particular case of the Paris attacks, our technology could effectively be that fire alarm for gunshots," said the company's CEO Ralph Clark.
We have these massive servers with loads of data which is not necessary, which is not needed, from people who are completely law abiding.
"[It would enable] law enforcement to get there perhaps one minute, two minutes sooner and be able to mitigate the downstream consequences of ongoing engagement of an active shooter."
By combining sensors with "smart" data analysis, software technology companies, including GE, have developed systems that can track people's movements - even in vehicles or situations where someone leaves a package on a rooftop.
The company says because the system only stores data when suspicious activity is detected - and deletes all other recorded material - its impact on a population's privacy is minimal.
"Unless an event has occurred the sensors are in a passive mode that is not really invading anyone's privacy," said Jim Benson, from GE's intelligent cities division.
But critics - including technology consultant Gemma Galdon Clavell - argue that unless citizens are made fully aware of the technology, and agree to its use, their privacy is going to be affected.
Clavell said cities have been too quick to install new technology that amounts to mass surveillance, and many are yet to see any useful results.
"We have these massive servers with loads of data which is not necessary, which is not needed, from people who are completely law-abiding," Clavell said.
"Then we take the money out of the traditional techniques that would have allowed us to identify specific persons that do pose a risk and follow them up thoroughly."
Ensuring citizens are comfortable with the way the data is used and making sure it is analysed in a way that is effective are major challenges. That's something cities around the world are contemplating while seeking to keep their citizens safe.
Source: Al Jazeera