An aerosol spray that makes unopened envelopes transparent so that the contents can be read has been invented.

"You spray it on and it temporarily makes the envelope clear," said Robert Schlegel, vice-president of the makers, Mistral Security, of Maryland. "It leaves an odor for 10 to 15 minutes, but there is no smudging of ink, no stain, no evidence at all. The envelope is transparent for a few minutes and you can respray it hundreds of times without leaving any stain."

The spray will be offered to police and secret services, including those in Britain. See-Through spray was developed to peer inside suspect packages such as letter bombs.

John Wadham, director of Liberty, the human rights organization, said that police would need a warrant to use the spray to examine letters.

But Simon Davies, director of Privacy International, a human rights group focusing on surveillance issues, said "This is an opportunity for governments to sidestep legislation on mail interception and opening. It is an ethically questionable product." 

Big Brother is being recruited to help people lose weight. Swiss scientists have tested the ability of the Global Positioning System (GPS)--a network of 24 navigation satellites orbiting the globe--to track people and gauge how much exercise they're clocking up.

The epidemic of obesity afflicting many Western countries has been blamed in part on a lack of exercise, and doctors agree that taking more would improve public health. But it's not clear how much exercise people actually take, and measuring it accurately has so far proved tricky.

Now Yves Schutz and his research group at the University of Lausanne in Switzerland have shown that GPS can help count the calories being burnt. Schutz monitored people while they walked or ran, using GPS receivers strapped to their backs. He was able to work out their precise position in three dimensions, and measure how far they went, and how fast.

By monitoring activity 24 hours a day, Schutz hopes to reveal why people are getting fatter. Beckie Lang, a nutritionist at Cambridge University, agrees the approach is exciting. Giving people GPS receivers might make them realize how little they actually do. But, she adds, to lose weight most people also need to stay off the crisps [potato chips] and croissants. 

To many parents, it may be a dream: A little gadget that can track where a child is at all times.

To many kids, it may be a fun thing: Their own cell phone, complete with a backpack shaped like a stuffed animal to house the global positioning technology that makes it all happen.

That at least is the vision of Susanne Mueller-Zantop, under whose guidance Siemens has developed a child's mobile phone with stepped-up monitoring capability.

The service is scheduled to debut in Germany and Great Britain next spring. Expected to cost between $100 and $200 for the hardware, and less than $20 a month for the service, the devices are intended for children between the ages of 3 and 11.

How does it work? Every 15 minutes, the child's phone communicates exact coordinates to a call center. Parents can phone into the call center to get information about their children's whereabouts.

A child can hit a button, providing instant location information to the call center which, in emergencies, can listen in on whatever the child's handset is picking up.

Schools in Belgium are considering a new electronic schoolbook computer system with an integrated chip that can locate students at all times. The idea is to hinder dropouts.

The system works via a login system: Every pupil's lesson schedule is logged into the system, and indicates when and where the children should be at all times during school hours.

"The teacher has a wireless receiver, the size of a key-holder, and every pupil is in possession of a chip-card which should be on him or her at all times," said Paul Vervinckt, producer of the system at Nedap Belgium. "If a teacher wishes to know where an absent or late pupil is, all he has to do is log onto his computer system, look up the kid's login number, and he'll be told instantaneously where the culprit is."

The Netherlands has been using the system with about 15,000 students for the past 15 months, with full approval of the Dutch Ministry of Education.

Big Brother never forgets a face. Or, at least, he won't if the State Department implements cutting-edge facial-recognition technology to track anyone entering or leaving the country.

A traveler's mug would appear not only on a passport or visa, but would also be digitized and entered into a massive database of smiles and grimaces. This would "enhance the security of [the nation's] borders [due to] increasing threats to U.S. citizens and property," according to an official State Department request for information recently issued to surveillance firms and obtained by Fox News.

The online collection of eyes, ears and noses would be used by Immigration and Naturalization Service agents to weed out fraudulent or duplicate applications, and to positively identify travelers and "minimize known security threats from excludable, criminal, or high-risk persons," the document says.

The software would attempt to match the live face of a border-crosser or visa applicant with the facial image under the same name in the database, and then do a cross-search to see if either face is also listed under another name.

Widespread use of the technology to track travelers is still under review, and implementation is at least a year away. Still, the State Department's Bureau of Consular Affairs is already busy making live facial scans of every Mexican citizen who applies for a "Border Crossing Card." Eight hundred thousand scans are on file so far, and about 115,000 images are added each month, according to the document.

It's not as if there isn't a bigger pool in which to dip. Most people have had their picture taken for something, which is why there are 1.1 billion facial images already in databases throughout the world, according to Visionics, a firm that specializes in facial recognition and other "biometrics" such as fingerprint scanning.

The State Department said it was premature to comment on the burgeoning program. Nevertheless, there conceivably could come a time when the face of every man, woman and child is digitized and connected to cameras posted in every government building and on street corners, tracking your every move as it scans for law violators.

Electronic surveillance may eat away your privacy in the digital era, but you'll get used to it. You have no choice.

Top lawyers told an Anglo-American law conference that governments had no other way to fight organized crime effectively in a digital age.

"I am convinced that covert surveillance is likely to prove the only effective answer to increasingly sophisticated crime," said Lord Justice Murray Stuart-Smith, the former overseer of MI5 and MI6, Britain's security and intelligence agencies. "Increasingly, the protection of the well-being of the many may require infringement of the rights of the nefarious few."

William Webster, a US judge who used to head the Central Intelligence Agency and Federal Bureau of Investigation, said tough measures might seem alarming today but people would get used to them. "Privacy must yield in some areas to the rights of others to be protected," he told the American Bar Association at a session in London.

Jeffrey Hunker of the US National Security Council said no one authority could police cyberspace and that states and private-sector companies would all have to work together.