Protection by detection

In the past 12 months, British schools have seemed less safe than ever before. First, the fatal stabbing of the headteacher Philip Lawrence while trying to help a pupil; then the horrific massacre at Dunblane; now a machete attack at an infants' school. How can we make our schools the haven for children that they ought to be? Part of the solution may come from the US - by a clever updating of radar.

Compared with the UK, American schools face far bigger problems. The routine carrying of weapons - knives and, worryingly, guns - is far more prevalent. The figures are staggering. According to statistics from the US Bureau of Justice, more than half of violent crimes against teenagers occur in school buildings, on school property or on streets near a school. An estimated 100,000 students carry a gun to school, and gunshots cause one in four deaths among American teenagers.

The carrying of weapons by children for self-protection has reached such epidemic proportions that many American schools have installed metal detectors at all entrances. But as we all know from our experience at airports, conventional metal detectors get it wrong a lot of the time - causing delays and frayed tempers - and only work at very short range. With more than 120,000 school buildings in the US, and an average of eight entrances per building, the search is on for a better system - one that is accurate, cost-effective and non-intrusive.

Now, an American company is experimenting with a device that will be able not only to detect concealed weapons from several metres away, but also to tell what sort of weapon it is. And the subjects will not even know they are being scanned.

The device, known as the Concealed Weapons Detection System, is being developed by The MacAleese Industries Inc, of New Mexico, and has been tested on the nearby Radar Range at the Sandia National Laboratories. It is based on a short-range version of radar.

First, a transmitter beams a pulse of radio energy at the subject. Most of the radio energy passes straight through the body, but a metallic object - such as a knife or a gun - will reflect or scatter some of the energy, which is then picked up by a receiver mounted in the same unit as the transmitter.

So far, this is not very different from the way in which the radar at an airport detects the presence of planes in the sky above it. But the clever part of this new device is the incorporation of software programmed to recognise the characteristic energy scatter patterns - the "signature" - for a wide variety of weapons, such as knife blades, derringers or larger- calibre pistols, and which can discriminate between a weapon and other common metallic objects such as belt buckles, coins or jewellery.

Controlled lab testing has produced a 99.2 per cent success rate for discriminating between weapons and innocent objects - far higher than conventional metal detectors, says the company.

For any building where security is important, the designers envisage a system comprising a complex but hidden array of antennae to provide total coverage of the approach to the door. When a person carrying a concealed weapon approached the door, the system would detect it and automatically engage an electronic lock to keep them out, while sending an alarm (either audible or discreet) to security personnel.

Schools are not the only ones that could benefit from this system. Banks and airports would be prime candidates. Taxi drivers could be protected too - now that attacks by passengers are increasingly common, if not commonplace. A concealed weapons system designed to cover the back doors could warn the driver and automatically lock the door before the passenger got in.

The crucial question is cost: if the device works but is too expensive, then cash-pressed British schools will never be able to afford to install it, and it will be only those organisations that can already afford to spend heavily on security that will use it. On this front, the news is equivocal.

"Our goal is to manufacture these devices for less than $3,000 per unit", said a spokesman for The MacAleese Industries. However, volume - or a government contract - might pull the figure down.

The company is also developing lightweight, hand-held versions of the device for police or military use in the US. For the police officer, a device with a range of 5m to 15m would allow the unobtrusive scanning of a suspect for concealed weapons before trying to make an arrest: this would lessen the risk to the arresting officer and reduce the likelihood of shooting an unarmed suspect. Such a device could also be used to scan large numbers of people arriving at or leaving an event. For the military, a more powerful backpack or vehicle mounted unit would allow long-range surveillance - up to 400m - and could be used to detect snipers or possible ambushes.