Home Office figures show that as a result of the spread in the use of such devices vehicle thefts have fallen by 20 per cent in the past five years.

Nationwide crime prevention campaigns launched by the Home Office to draw attention to the high cost of vehicle and domestic thefts and the need for better security to protect property, have helped persuade car manufacturers to install sophisticated security devices on expensive models which are often targeted by thieves.

The development is also being moved ahead rapidly by the involvement of insurance companies which now recognise the fact that it makes better business sense to offer lower insurance premiums and higher no-claim bonuses to drivers who fit approved alarm devices on their vehicles to minimise the risk of theft.

According to the industry the three most popular security devices are high decibel alarms designed to scare away intruders, electronic or mechanical immobilisers which prevent cars from being driven away and highly sophisticated devices that help police to track down stolen cars within hours of a report being made.

A small radio tracking electronic box hidden in the body of the car, which is distributed in Britain by Tracker Ltd and Securicor's TrakBak, begins transmitting a radio signal as soon as the car is reported missing, enabling a special police vehicle to home in and recover it.

Miniaturisation technology is being used in car security. A high quality miniature digital camera concealed in a car takes the thief's photograph as he breaks into the vehicle.

Developed by British firm TOAD Innovations, the TOAD Eye in-car security device's pictures are securely contained in a cartridge inside a tamper-proof "black box'' control unit which co-ordinate the operation of the camera. A matchbox size personal downloading cartridge then permits the images to be transferred to a compatible computer.

The commonest and most effective security device is the simple noise alarm for cars and homes which is easily fitted by Do-It-Yourself enthusiasts.

But technology is being exploited in other more interesting ways. Last November, an alarm system pioneered by Norfolk police in eastern England, beat 12 other finalists to win the European-wide Crime Prevention competition award.

The winner, Norfolk Domestic Violence Linkline (NDVL), is a partnership between Norfolk Constabulary, Norwich City Council, and Norwich Crime Prevention Panel victims. People at risk wear alarms as pendants around their necks or in their pockets linked by radio to a telephone. When they press a button, it alerts an operator in a control room who calls in the police.

More importantly, when activated, every conversation can be recorded to help police build up evidence. Since the scheme was introduced some 18 months ago, 100 women have been issued with the alarms and the police have reported a dramatic increase in detection and arrest of offenders.

Home Office Minister Alun Michael commented: ``Users of the scheme say it has reduced their fear and allowed them to lead a normal life. The project demonstrates just how much can be achieved by preventing crime when local agencies work together and pool their resources."

Nowhere is the presence of a security alarm now more welcomed than inside the ubiquitous computer for personal or business use. With the rising increase in computer usage in British homes (there are more computers per head of the population in Britain than any European country), the theft of processing chips is developing into a growth industry.

A new type of computer alarm system, the Nightwatch, developed by Premier Electronics (UK) Limited, based in Swansea, Wales, is designed to frustrate any attempts to remove the whole computer or the chip from the premises both during the day and in the night.

Armed by a single key, a movement sensor inside the Nightwatch device triggers an alarm if someone attempts to move the computer. Even if the thief manages to defeat this and attempts to remove the chip without shifting the whole computer, a second sensor triggers the alarm as soon as the machine's cover is removed. The movement sensor can be disabled for normal operation during the day.

For business network computers, a total of eight personal computers can be loaded and linked together with Nightwatch cards using cables provided. If a single machine is removed from the network, all the computers in the link will raise the alarm, provided by a piercing 115 decibel sounder.

Moreover, Nightwatch system can also be linked to an existing intruder alarm system so that any tempering triggers the main alarm system, which will alert the police station or a monitoring centre. For total effectiveness of the system, it is installed with its own internal battery back-up to guard against power-cuts or deliberate interruption of the supply.

Premier Electronics (UK) Limited, Unit 2
Glan Llwyd, Pontardulais, Swansea, United Kingdom, SA4 1RS
Telephone/Fax: +44 1792 885044

TOAD Innovations, The Quorum
Barnwell Road, Cambridge, United Kingdom, CB5 8RE
Telephone: +44 1223 214555
Fax: +44 1223 214844