Tens of thousands of Britons are being covertly tracked without their consent in a technology experiment which has installed scanners at secret locations in offices, campuses, streets and pubs to pinpoint people's whereabouts.

The scanners, the first 10 of which were installed in Bath three years ago, are capturing Bluetooth radio signals transmitted from devices such as mobile phones, laptops and digital cameras, and using the data to follow unwitting targets without their permission.

The data is being used in a project called Cityware to study how people move around cities. But pedestrians are not being told that the devices they carry around in their pockets and handbags could be providing a permanent record of their journeys, which is then stored on a central database.

The Bath University researchers behind the project claim their scanners do not have access to the identity of the people tracked.

Eamonn O'Neill, Cityware's director, said: "The objective is not to track individuals, whether by Bluetooth or any other means. We are interested in the aggregate behaviour of city dwellers as a whole. The notion that any agency would seriously consider Bluetooth scanning as a surveillance technique is ludicrous."

But privacy experts disagree, pointing out that Bluetooth signals are assigned code names that can, to varying degrees, indicate a person's identity.

Many people use pseudonyms, nicknames, initials, or abbreviations to identify their Bluetooth signals. Cityware's scanners are also picking up signals that are listed using people's full name, email address and telephone numbers.

Contacted about the Cityware project, the office of the information commissioner said in a statement that the public should "think carefully" before switching on their Bluetooth signals. A spokesman said the government watchdog would "monitor" the experiment.

"This is yet another example of moronic use of technology," said Simon Davies, director of Privacy International, an independent campaigning group defending personal privacy. "For Bath University to assert that there aren't privacy implications demonstrates an astonishing disregard for consumer rights. If the technology is as safe as they claim, then all the technical specifications should be published and people should be informed when they are being tracked."

He added: "This technology could well become the CCTV of the mobile industry. It would not take much adjustment to make this system a ubiquitous surveillance infrastructure over which we have no control."

Although initially confined to Bath, Cityware has spread across the planet after the software was made freely available on the internet sites Facebook and Second Life. Thousands of people downloaded the software to equip their home and office computers with Cityware scanners.

More than 1,000 scanners across the world at any time detect passing Bluetooth signals and send the data to Cityware's central database. Those with access to the database admit they do not know precisely how many scanners have been created, but there are known to be scanners in San Diego, Hong Kong, Australia, Singapore, Toronto and Berlin.

In Bath alone scanners are tracking as many as 3,000 Bluetooth devices every weekend. One recent study used the scanners to monitor the movements of 10,000 people in the city.

About 250,000 owners of Bluetooth devices, mostly mobile phones, have been spotted by Cityware scanners worldwide.

O'Neill, who described his project as "public observation" rather than surveillance, said the data would improve scientific understanding of the privacy and security threats posed by Bluetooth technology. A "potentially immensely valuable side-effect", he added, was that data about people's movements could help research into the spread of biological epidemics.

"Just as we continue to research forms of defence against other more traditional threats, we must research forms of defence against new digital threats," he said, adding that the database eventually would be destroyed.

However Vassilis Kostakos, a former member of Cityware who now does Bluetooth experiments on buses in Portugal for the University of Madeira, accepted such tracking was a problem.

"We are actually trying to fix this," Kostakos said. "If a person's phone is talking to a scanner, then they should be told about it. Any technology can have good and bad consequences. In many ways, I think the role of a scientist is to point out both. I agree this is complex and I agree there are harmful scenarios."

The technique has echoes of the thriller Enemy of the State in which the character played by Will Smith is followed by satellite surveillance.

Kostakos said he could foresee complex ways in which criminals could exploit the technology, adding: "I recently tried to look at people's travel patterns across the world, and we [saw] how a unique device which showed up in San Francisco turned up in Caracas and then Paris."

Bluetooth tracking technology is already being used to aim advertisements at people, for example as they walk past shops or billboards.

Bluetoothtracking.org, a website based in the Netherlands, is using the same technology to publish live data about people's movements across the town of Apeldoorn. The facility allows people to search the whereabouts of friends and associates without them knowing about it.

Some scientists using the technology describe a future scenario in which homes and cars adapt services to suit their owners, automatically dimming lights, preparing food and selecting preferred television channels.