The handheld multimedia device the size of a pocket organiser allows visitors walking or cycling through the city to see what the Wall looked like at the spot where they are at a given moment, using GPS navigation technology.

The MauerGuide (WallGuide) presents pictures, video footage and audio recordings about the Wall at prominent sites including the historic Brandenburg Gate and the former Checkpoint Charlie border crossing.

In English and German, the guide also allows visitors to avoid herds of tour groups and find their way on their own.

Of the 155 kilometres (96 miles) of grey concrete that cut off West Berlin from its hinterland for 28 years, only three kilometres in total is still standing.

It was chiseled apart by Germans from East and West euphoric over the opening of the border in 1989 and large slabs were sold off to foreign buyers.

Nearly 20 years on, visitors to the city centre can rarely differentiate between the former East and West, both of which have seen a dramatic construction boom since the Wall was torn down in a peaceful popular uprising.

Manufacturer AntennAudio, a unit of US media company Discovery Communications that makes audio guides for museums, said the Berlin gadget was a novelty.

"It was a challenge," said Rosemarie Wirthmueller, who runs the company's Berlin office. "We dug in all the archives we could find."

She said demand had been brisk since the product was introduced in May at the Checkpoint Charlie museum where caravans of tour buses stop every day. Some 500 guides are now in circulation.

The guide meshes with plans by the Berlin government to preserve the history of the despised Wall erected in 1961 by the communist regime of East Germany to stop a mass exodus of its citizens.

-- Visitors can watch an East German border guard fleeing West --

"MauerGuide presents a well-documented and customised account of history that is appealing to tourists and fits nicely with our overarching memorial plans for the Berlin Wall," the municipal state secretary for culture Andre Schmitz said when the project was unveiled in April.

The city-state's government in 2006 announced a 40-million-euro drive to preserve remnants of the Wall.

Users of the guide can tour the Wall's former course at their own pace, renting the guide for a few hours or up to two days, at a rate of between four and 15 euros (about six to 24 dollars).

The longest tour covers 15 kilometres with 22 stops, beginning at the Bernauer Strasse, a street seared into television viewers' minds in the early 1960s when they saw panicked residents jumping out of their apartment windows to reach the West.

Those images can also be seen on the MauerGuide screen.

The tour ends at the East Side Gallery, a stretch of Wall 1.5 kilometres long that was decorated with murals by dozens of prominent artists in 1990, the year Germany unified.

At each stop, the guide provides historical background, archive pictures, videos and witness accounts of some of the most harrowing chapters of the Cold War -- making up five hours of documentation in all followed by a quiz.

Well-known sequences include the image of a young East German border guard leaping over barbed wire to flee to the West in 1961 and a press conference with East German leader Walter Ulbricht in which he states "No one has the intention to build a wall" -- two months before he closed the border for good.

Visitors can also watch bygone street demonstrations, daring attempts to escape the Stalinist state and wrenching images of those caught in the process.

One was 18-year-old Peter Fechter, who was shot by East German border guards while trying to flee over the Berlin Wall. He was left to bleed to death for an hour as horrified West Berliners, unable to intervene, looked on.

The MauerGuide shows photographs of the agonising scene taken in East Berlin that the feared Stasi secret police later confiscated.

Victims groups estimate that more than 1,000 people died trying to escape East Germany, many of them shot by communist border guards.

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