A surveillance state, with cameras on every street is commonplace but now Big Bizniz is also turning to Kid Sister.

Face recognition, behaviour analysing surveillance cameras, biometric profiling and the monitoring and storing of our shopping patterns has made snooping into our habits, movements and private lives ever easier.

Dismayed at its shrinking power to market to us via traditional media or even the internet, the private sector is now proposing to reach potential customers in ways that critics say should have us all concerned.

"There is an enormous pent-up demand for personalised location advertising, whether it is on your cellphone or PDA, on your radio in your car, or on the billboards you walk by on the streets and inside stores," says Bruce Schneier, chief security technology officer of BT.

"This is yet another technological intrusion into privacy. And like all such intrusions, it will be taken as far as the owner of that intrusion finds it profitable."

Emotional reactions

New surveillance technology could even evaporate the advertiser's favourite grouse that "half of advertising is wasted, but we don't know which half".

Advertisers are turning to "intelligent" digital billboards that use cameras to watch you watching the ads.

In Germany, developers have placed video cameras into street advertisements attempting to discern people's emotional reactions to the ads, according to the Washington-based privacy advocate outfit the Electronic Privacy Information Center (EPIC).

It warns that this type of surveillance encroaches on civil liberties. Such face, voice and behaviour technology could be a means of tracking individuals on a mass level across their entire lives, it says.

Pushed by the demands of advertisers and security-minded governments, these technologies are becoming so increasingly smart and intrusive that they now resemble something out of science fiction, it warns.

Science fact

Some of the technology available now seems to have overtaken fiction.

When an interactive ad shouts out to Tom Cruise's character in the 2002 film Minority Report: "John Anderton, you could use a Guinness!" It identified him as he walked through a mall by scanning the unique pattern of his iris.

This is now pretty standard. Face recognition technology is proving to be a handier, more sophisticated tool to pick us out on the street, a crowded room or at passport control.

Such systems are able to automatically detect and identify human faces using recognition algorithms.

The first step for a facial recognition system is to recognise a human face and extract it from the rest of the scene. Next, the system measures the distance between the features -- a distinctive aspect of our faces that does not change with disguises or even surgery.

Matches can then be found in databases in under a second, although 100% accuracy is not yet guaranteed.

Currently the private sector is finding such systems useful for what it calls "targeted marketing," or "dynamic advertising."

Japan's NEC, for instance, sells face-recognition technology to allow advertisers to tailor what ad is showing on a digitised screen depending on the viewer's sex and age.

Tracking systems, such as these, can determine the viewer's gender 85-90% of the time, approximate age and ethnicity, and change the ads accordingly.

NEC denies the system raises privacy concerns as it does not store any images, only the analysed results (age and sex) based on those images.

But as Schneier points out systems like these are likely liable to "function creep" where a technology is brought in for one purpose, to profile your sex while viewing an ad for example, and then begins to push the boundaries.

"Once the cameras are installed and operational, once they're networked to central computers, then it's a simple matter of upgrading the software," he says.

"And if they can do more -- if they can provide more "value" to the advertisers -- then of course they will. To think otherwise is simply naive."

And when advertisers start to follow us, our privacy, our right to be left alone will be severely compromised, he thinks.

More control

Democratic governments, charged with protecting us from such violations, are beginning to wake up to these practices.

The US is about to propose a bill to ensure that consumers know what information is being collected about them. The EU promises to rigorously police what it claims are already stringent controls on our personal data.

"Europeans must have the right to control how their personal information is used," Viviane Reding, the EU's commissioner for information society and media told BBC news. "We cannot give up this basic principle, and have all our exchanges monitored, surveyed and stored, in exchange for a promise of 'more relevant' advertising."

Despite such assurances, given the pervasiveness of such technologies firstly on the internet and now spreading to the physical world, what we do about them in the next few years will be crucial. It might control our privacy for generations to come say human rights advocates.

"Companies are increasingly impatient to get to us and once these practices are commonplace it will hard to reverse them," says Marc Rotenberg director of EPIC. "Particularly as, ironically, we lose privacy these companies are gaining secrecy."

It would seem sensible to debate now how far business and the state should be allowed to tag us while we still have a privacy to protect.

Kid Sister: Control (LA Riots Remix)