A new exhibition in Prague reveals the spy technology used by the communists—and their opposition—in former Czechoslovakia.

It comes ahead of the 30th anniversary of the Velvet Revolution, when anti-communist protests toppled the regime.

The exhibition includes microphones hidden in watches, tiny micro cameras, and tape recorders hidden in suitcases.

“Because we are in the technical museum we emphasized the technology used by the Communist secret police or the Nazi regime to keep in power, but also the technology used by the opponents of those regimes to get freedom,” says Jan Hostak, the museum’s curator.

The heavily guarded Iron Curtain was traced by an electrified barbed-wire fence intended to isolate the communist world from the West.

As the objects show, spying was a massive business.

“The secret police agents were masters in bugging and eavesdropping on people and no dissident could be certain that his or her apartment were not targeted,” says Hostak.

The exhibition is called “The Technology in Dictatorships” and is now showing at Prague’s National Technical Museum.