The hi-tech spy

James Bond's briefcase looks decidedly low-tech compared to today's equipment

The American spy plane forced to land in China was chock-full of electronic surveillance equipment. Today, espionage is all about who has the best technology.

The diplomatic fallout surrounding an American spy plane forced to land on Chinese soil has again highlighted Washington's desire to keep a watch on the rest of the world.

It's also a reminder that when it comes to intelligence gathering, the hackneyed image of a crafty spy with a miniature camera is somewhat out of date.

So what sort of hi-tech practices do governments favour these days if they want to keep tabs on foreign powers?

Satellite listening

The widely acknowledged leader in this field is Echelon, a network of listening posts run by the United States National Security Agency (NSA) and located in America, Canada, Australia, New Zealand and the UK.

Menwith Hill, in Yorkshire, is a key link in Echelon

While the idea of such a network was first agreed between London and Washington in 1948, for years the US denied its existence. It was eventually confirmed in declassified NSA documents.

Echelon's capabilities are awesome. Relying on a network of American satellites, the system picks up microwave signals used by mobile phones. At any one time, millions of calls are recorded and then checked against a powerful search engine designed to pick out key words that might represent a security threat.

Its work has been effective in tracking down terrorists but, says Ian Synge of Jane's Sentinel, most governments have started to shy away from microwave communication.

Underwater bugging

Alongside Echelon the idea of physically sticking bugs on underwater communication cables looks remarkably hands-on. Yet experts speculate it still goes on.

Satellite technology is not new. This image dates from 1960

During the 1970s, Soviet ports were secretly infiltrated by an American "spy submarine" with deep-sea divers on-board, who attached listening devices to telephone cables. After several weeks the divers returned to the scene and picked up the device, along with many hours of taped conversations.

Animosity between America and Russia has declined, but according to the investigative reporter and surveillance expert Duncan Campbell the US still maintains a submarine specially equipped for such duties.

Likely targets may include those in the Middle East, Mediterranean, eastern Asia, and South America, says Mr Campbell.

Computer bugging

While the right to monitor e-mail and internet activity is openly defended by the likes of the British government, more underhand methods can be used to track computer use.

Advances mean satellite imagery is much clearer these days

Latest advances in listening technology mean that if a bug can be attached to a computer keyboard it is possible to monitor exactly what is being keyed in. Because every key on a computer has a unique sound when depressed, it's simply a case of translating the clicks into words.

The threat of this technology has led some internet banks to rely on a degree of mouse movement.

Visual spy satellites

Spy satellites revolutionised US intelligence gathering intelligence during the Cold War. Washington had relied on high-altitude reconnaissance aircraft, such as the U-2, to gather photographs of Russian and Chinese military installations.

As well as being vulnerable to ground fire, the U-2 fleet could only cover so much distance. The maiden mission of the Corona photo-satellite in 1960 collected more images than the whole U-2 program had taken in four years, according to Jeffrey Richelson, author of America's Secret Eyes in Space.

Every click of a key can be transcribed

Unfortunately, Corona could not transmit its pictures back to base - its film fell to earth in a capsule.

Great advances in satellite technology have followed, but Ian Synge says stories that they can read a newspaper headline from hundreds of miles up are probably apocryphal.

Nevertheless, spy satellites remain a valuable source of intelligence. Even commercial satellites have an image resolution of one metre - easily good enough to track the movement of tanks and most military hardware.

Radar imaging can pierce cloud cover and even expose subterranean development - useful if you suspect the enemy of stockpiling arms underground.

Laser microphones

The net curtains are more than just an aesthetic addition

Why have so many government offices got net curtains? One reason is that without them spies would be able to eavesdrop on top-secret conversations almost effortlessly.

Laser microphones can pick-up conversations from up to a kilometre away by monitoring window vibrations. Curtains are a simple antidote, since they help absorb the sound and so corrupt any signal.

Despite the fact computer technology has led to quantum leaps in intelligence gathering, low-tech still has its place.

"One of the favourite stories I once heard from the Cold War was the KGB lesson that you could do one of two things to find out what the president's advisers are saying," says Ian Synge.

"One was to find a sympathetic source inside the White House who could feed you information. The other was to take out a subscription to the New York Times."