BEIJING -- Tens of thousands of taxi drivers in Beijing have a tool that could become part of China's all-out security campaign for the Olympic Games. Their vehicles have microphones -- installed ostensibly for driver safety -- that can be used to listen to passengers remotely.

The tiny listening devices, which are connected to a global positioning system able to track a cab's location by satellite, have been installed in almost all of the city's 70,000 taxis over the past three years, taxi drivers and industry officials say.

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