The shop assistant was hidden from view when he broke off a phone call to shout: "I will be with you in a minute. I can see you." There seemed little reason to doubt his word. A bank of monitors behind the front window indicated that he had the benefit of perhaps half a dozen cameras concealed around the room.
The devices form part of the expanding range of visual, audio and chemical sensors offered at Spycatcher, the British retailer of surveillance and espionage equipment. As Paul Danziger of Spycatcher puts it: "More and more people are paranoid and are looking for equipment that can detect things."
Spycatcher is not the only business to have noticed a rapid rise in demand for sensors, which are loosely defined as devices designed to detect physical or chemical stimuli.
The global market for some specialised instruments is growing particularly rapidly, fuelled less by paranoia than by technological advance allied to a corporate need to improve process efficiency and satisfy increasingly strict environmental regulations.
The pace of development across all markets has been made possible by the mass production of the digital electronic systems used in sensors. "We have got so much processing power so cheaply that it becomes cost-effective to control many more machines and devices," says Rob Bogue, who runs a financial and technical consultancy that advises Britain's Environment Agency. "We are looking at more things with sensors now than ever before."
The size of the sensors market is notoriously hard to estimate. The supply side is fragmented, with no dominant companies, and diverse, with tens of thousands of products varying in price from less than $1 to more than $1,000.
Malcolm Burwell, a vice-president of Absolute Sensors, estimates annual sales of sensors for use within industry at about $3 billion, rising as high as $33 billion when devices employed in clinical testing, cars, aircraft and household goods are included. "I think it's fair to say that all the sensors [markets] are growing at 8, 9 or 10 per cent," he says. "But the real challenge is to find the 30 per cent markets in there."
These opportunities are to be found increasingly in industries under commercial or regulatory pressure to improve their performance. Demand for chemical and gas sensors is rising fast as companies perform more environmental analyses to comply with laws related to health at work and discharges of waste.
The car industry has been forced to invest heavily in temperature, position and pressure-measuring devices to increase vehicle fuel efficiency. Reed Business Information forecasts carmakers' total spending on sensors will rise from $3.1 billion in 1998 to $4.2 billion by 2002.
The step up in commercial interest has stimulated both academic and corporate research, reflecting a heightened appreciation that most processes can be improved by the judicious use of a sensor. As Bogue says: "It's a business which offers enormous opportunities for companies that can come up with technology to perform functions that haven't been done before."
The history of the charge-coupled device (CCD) shows how far-reaching the effects of sensor innovation can be. The instrument, which allows the detection of very low levels of light, has replaced conventional techniques in equipment ranging from surveillance cameras to machines for scanning baggage at airports.
They have revolutionised astronomy, says Dr Paul Jorden, principal applications engineer at EEV, which is part of General Electric. "People want to look further into the universe and at fainter things," he says. "CCDs are the way to do that."
He Jorden says there are still many more potential uses for CCDs, which can enhance the quality of dental X-rays and improve the effectiveness of machines used to check defects in manufactured goods. The latest growth area is satellite positioning, which promises to increase in importance as the number of spacecraft launches increases each year.
The growing sophistication of devices such as CCDs makes it unlikely that a handful of companies will emerge as market leaders in the sensors industry as they have in PC processors. It is difficult, as Malcolm Burwell says, to design a device that will work equally well in a moulding machine and a plant manufacturing nitric acid.
Even relatively large and diversified manufacturers such as EG & G, the US engineering group, see little future in introducing the kind of mass production of sensors that sensors themselves are designed to improve. "Most of it is very application-specific," says Greg Summe, its chief operating officer. "They [the customers] have a need to get something done and we work with them to design a sensor to fit that need."
Despite this, he says there is still plenty of room for growth in the industry. About 90 per cent of sensors are mechanical, and most of those will be replaced eventually by superior electronic devices. Most importantly, there are technological challenges that, once passed, will open huge potential markets. Considerable effort has been focused, for example, on building a machine that can register the presence of minute quantities of drugs and explosives. Paul Danziger of Spycatcher says there are lots of other applications waiting. When it comes to devising new types of sensor, he concludes, "imagination is unlimited".