A police surveillance camera mounted to a lamppost on a quiet suburban road in Beijing has one target: the turquoise door to the home of the artist and activist Ai Weiwei. The camera was installed two years ago, as Ai's blogging, tweeting, and art increasingly challenged the Chinese government's authority. This spring, during Ai's 81-day detention, it was a reminder of the omnipresence of the government. Afterward, it captured throngs of visitors, many of whom flung money over his gate to help him pay a $2.4 million tax bill. The camera remains in place during his continuing house arrest; now it's decorated with a red lantern marking National Day of the People's Republic of China.