Several street peddlers selling baked sweet potatoes equipped themselves with interphones to avoid occasional raids by urban management officers near Huawei Bridge in Chaoyang district of Beijing, the Beijing News reported on Tuesday.

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The vendors, scattered every 50 meters near the 3rd Ring Road in East Beijing, wore headphones connected to their intercoms and got themselves ready to inform the others when urban supervisors turned up.

The signals of each phone can cover one square kilometer. According to a seller surnamed Jin, he had been caught by the patrolling supervisors several times in the past year. "They confiscated our tools or charged for 200 yuan ($30) of fine," he said.

Jin earned 60 to 70 yuan per day. And the cost of his chemical tin and tricycle was 300 yuan. "A 200-yuan interphone is worthwhile to buy as it can greatly reduce the risk of being caught," he said.

According to the Beijing Radio Management Bureau, they cannot judge the legality of the interphones of the peddlers. However, owners should register their interphones before using them.