Sophisticated sensors are opening the door to better protection against intruders. By Paul Gosling
Imagine the scene: you walk up to your front door and it opens - but only because it is you. Inside, all your valuables are fitted with their own sensors and a local security firm is alerted if they are moved from their rightful place. Using hidden cameras, security officers can see if burglars have broken in, or whether it was just the cat being clumsy and knocking things off the shelf.

While this picture of domestic security is still something of the future, there is already a similar industrial control system today. And it is an arrangement householders will find themselves moving towards in a hurry. Since April, no police force has responded to burglar alarms that are regularly wrongly activated - and 92 per cent of alerts are false alarms - unless there is supporting evidence of a break-in. Instead, buildings will increasingly be protected by networks of electronic devices linked to private security firms.

At its Cambridge research laboratories, the Italian electronics giant Olivetti has installed what it calls the "Active Badge" system for both security and staff management. Every member of staff has a personal infra- red badge that reacts with sensors throughout the complex.

"As you approach a door it runs a check to see if you are allowed in," says Peter Rennison, an Olivetti spokesman.

The system also controls access to computers and triggers alarms if important equipment is moved. The badges allow the whereabouts of staff to be monitored constantly, partly as a means of controlling their work, but also to track them down for phone calls. Closed-circuit television confirms and records what is happening at all times.

Olivetti says that despite the Big Brother implications of the Active Badge system, staff have been won over by its benefits - particularly the improvements in communication. The badges, which double as pagers, even notify employees that the sandwich-seller has arrived.

The company has begun to market the Active Badge system, and the Budapest police force is among its first customers. A basic system of six sensors and six badges costs as little as pounds 2,000. One of the most obvious applications, according to Olivetti, is in hospitals, which are highly susceptible to theft. They are packed with extremely valuable equipment, but controlling the movement of visitors is difficult.

The company is also intending to market a version of the Active Badge for elderly or vulnerable people. It would be able to monitor pulse rates, automatically calling an ambulance if the wearer fainted or had a heart attack.

The main drawback of the system is that access is totally dependent on the badge, which can be lost or stolen. Alternatives, such as voice and hand recognition, or PIN numbers, are being tested. Another idea being considered is to insert a controlling chip into shoes - but what happens when you change your footwear?

For today's home-owners, the main problem with home security systems is that the deafening burglar alarm is often ignored. Even if you are paying a security firm to monitor your premises, there is no way of discovering whether it is a false alarm or a genuine break-in. But if your alarm is linked to either a camera or a microphone within the home, security officials can check on what is happening and act.

A CCTV system would be the most sophisticated monitoring option. But at pounds 1,500 for a basic system, this is beyond the pocket of most householders. A cheaper alternative is a tiny still camera in a 1cm chip, developed by Vision, a company that began life at Edinburgh University. Starting at little more than pounds 100, it will take digital snapshots of any housebreakers when activated. But, of course, it has to be pointing in the right direction.

Sensitive, multi-directional microphones can be equally effective, starting at pounds 500 for a unit, transmitting suspicious sounds to the security firm by radio. They are expected to take a quarter of the market in sales of security devices over the next few years.

You can also get instant vengeance on intruders , thanks to the so-called smart water system. Developed by Probe FX, it is a water-based dye which is sprayed from sprinklers and marks intruders. Several large retailers have installed the system and it has helped to secure a conviction in Staffordshire.

With the development of smart network systems, such as Novell's NEST, you will be able to keep tabs on your home from almost anywhere. You can already buy a gadget which pages you if your burglar alarm is triggered. With NEST installed, you could then video-phone home and alert the police if there is a break-in. Just as useful, you could close the window if the problem turns out to be a curtain blowing in the wind.